The AAC24 workshop is a by-invitation biennial forum for intensive discussions on long-term research in advanced accelerator physics and technology. Since its inception in 1982, the AAC Workshop has become the principal US meeting for advanced particle accelerator research and development with strong international participation. We are anticipating over 250 scientists and research leaders in particle-beam, laser, and plasma physics to participate in this year’s meeting. This research supports the development of capabilities for the basic sciences, from photon science to high energy physics, as well as the development of compact accelerators for industrial, medical and security applications.
The AAC24 Workshop will host multiple working groups:
We look forward to seeing you in July of 2024!
From its inception, the Advanced Accelerator field has considered future colliders as the ultimate goal of high-gradient accelerator technology [1]. In the decades that followed, there has been rapid experimental progress [2,3,4] and a conceptual evolution of what future colliders based on Wakefield Accelerator (WFA) technology might look like. The recent P5 Report [5] calls for “vigorous R&D toward a cost-effective 10 TeV pCM collider based on proton, muon, or possible wakefield technologies.” Specifically, the P5 Report requests “the delivery of an end-to-end design concept, including cost scales, with self-consistent parameters throughout.” In this presentation, we will outline the requirements and challenges for a 10 TeV WFA collider. We will describe a community-driven design study based on working groups and performance metrics to produce a unified 10 TeV collider design concept, including a timeline with deliverables. Finally, we will discuss funding scenarios for this multi-year, multi-FTE effort.
[1] R. Ruth et al. “A Plasma Wake Field Accelerator” Particle Accelerators 17, 171-189 (1985)
[2] E. Esarey et al. “Physics of laser-driven plasma-based electron accelerators” Rev. Mod. Phys. 81, 1229 (2009)
[3] C. Jing “Dielectric Wakefield Accelerators” Rev. Accel. Sci. Tech, 9, 127-149 (2016)
[4] M. Hogan “Electron and Positron Beam–Driven Plasma Acceleration” Rev. Accel. Sci. Tech, 9, 63-83 (2016)
[5] P5 Report https://www.usparticlephysics.org/2023-p5-report/
Advanced accelerator concepts have potential to enable future colliders. Recent progress includes multi-GeV acceleration, positron acceleration, strong structure loading and focusing, staging of two modules, beam shaping for efficiency, high gradient structures and greatly improved beam quality which recently enabled wakefield-based FELs.
The recent 2023 Particle Physics Project Prioritization (P5) report describes priorities to guide work over the coming decade. Generic R&D is important to extend the reach of accelerators. This is important to future colliders and stewardship of nearer-term applications with broad benefit. R&D attracts high-level talent important to develop machine design and projects.
To follow the HL-LHC and a Higgs Factory, R&D should be pursued towards the 10 TeV parton center of momentum (pCM) scale by colliding muons or protons, or possibly an electron-positron (or gg) collider based on wakefield technology. To make an informed decision — one we hope to make within the next 20 years—one or more concept must reach technical maturity, allowing reliable estimation of cost and risk.
Wakefield collider concepts are in the early stages of development, with conceptual parameter sets developing. An end-to-end design concept, including cost scales, with self-consistent parameters throughout is an important next step requiring focus and engagement with the collider and high energy physics communities. Experiments and test facilities should be used to demonstrate acceleration and beam requirements of a stage for a future collider based on wakefield technology, operation with two linked multi-GeV stages, and methods to reduce cost and risk, guided by collider R&D.
European research groups and institutions, often working in close collaboration with others from around the world, work on all aspects of advanced accelerator research.
In this talk I will give an overview of research efforts in Europe, highlight recent key results, and indicate anticipated future directions.
The first demonstrations of fully optical multi-GeV laser wakefield acceleration (LWFA) have been enabled by the advent of low density (~$10^{17}$ $cm^{-3}$), meter-scale plasma waveguides generated in supersonic gas jets [1-7]. In this talk, I will present results from our recent LWFA experiments using plasma waveguides up to 30 cm in length, which have produced sub-milliradian divergence electron bunches with nC-level charge in the 1-10 GeV range [6,7]. I will also discuss our extensive simulation efforts, which are motivated by physics understanding and optimization of accelerator performance. These efforts include models of meter-scale hydrodynamic waveguide formation and their experimental benchmarking [8], and new, important regimes of LWFA drive pulse propagation [5] that strongly affect the laser wakefield acceleration dynamics. Finally, I will discuss the use of consistent, high charge multi-GeV electron bunches to generate muons in high-Z materials.
Funding Acknowledgements: This work was supported by the U.S. DoE (DE-SC0015516, LaserNetUS DE-SC0019076/FWP#SCW1668, and DE-SC0011375), NSF (PHY2010511), DARPA’s Muons for Science and Security Program (MuS2). Simulations used DoD HPC support provided through ONR (N00014-20-1-2233). E.R. is supported by NSF GRFP (DGE 1840340). Portions of work prepared by LLNL under Contract DE-AC52-07NA27344.
[1] Feder et al., Phys. Rev. Res. 2, 043173(2020).
[2] Shrock et al., Phys. Plasmas 29, 073101(2022).
[3] Miao et al., Phys. Rev. X. 12, 031038(2022).
[4] Miao et al., Physics Today 76 (8), 54-55(2023).
[5] Shrock et al., Under review, arXiv:2309.09930(2023).
[6] Shrock et al., In preparation(2024).
[7] Rockafellow et al., In preparation(2024).
[8] Miao et al., Under review, arXiv:2404.13632(2024)
Laser-accelerated electron beams have been the subject of intense research in the last few decades. The general direction in the field is the development towards ultralow beam emittance, necessitating controlled injection methods to ensure electron trapping in the laser-driven plasma wave. Due to its simplicity, one of the more popular injection mechanisms relies on a downward step in gas density created by a shock wave oriented perpendicularly to the wakefield propagation direction. Upon crossing this step, the plasma wave breaks and locally injects a bunch of electrons, leading to quasi-monoenergetic electron bunches due to the uniform acceleration distance for all particles. A main drawback of this scheme is the fact that this braking wave injects the electrons into a phase of the wake that is close to the zero-field crossing, leading to a significantly reduced electron energy compared to the self-injection scheme yielding broadband pulses. The consequence has been an energy limit of approx. 1 GeV for such shock-injected bunches. With a novel optical method to generate the shock, we can gain additional degrees of freedom such as a flexible density ratio before and after the shock, allowing to shift the injection point more into the high-field phase of the plasma wave. Using this approach, we have recently demonstrated 2-2.5 GeV, monoenergetic electron beams from our ATLAS laser facility. Such beams are intended to drive our experiments into Breit-Wheeler pair creation in the non-perturbative regime.
Future applications of laser-plasma accelerators will require one or more stages providing multi-GeV energy gain. Preformed plasma channels can increase the maximum energy gain of a laser-plasma accelerator. Recently, hydrodynamic optical-field-ionized (HOFI) plasma channels [1-3] have gained attention because i) they produce tightly confined channels at densities required for multi-GeV acceleration, and ii) contain no external structure making them ideal for >kHz operation. In the first half of the talk, we discuss high-quality beam production in HOFI plasma channels. We explore the use of a density down-ramp generated between neutral gas immediately prior to the channel and the channel itself to trap electrons. We demonstrate generation of 1.2 GeV bunches with percent-level energy spread, using sub-100 TW laser pulses [4]. In the second half of the talk, we discuss experiments to guide PW-scale pulses in 30-cm-long HOFI plasma channels. Understanding how the laser pulse evolves in the spatial and temporal domain during propagation is critical for high energy gain, and maintaining high bunch quality during acceleration. We present experimental results investigating drive laser propagation in HOFI plasma channels at the BELLA PW laser. We demonstrate conditions under which the channel can be tailored to match the drive laser focus at plasma densities suitable for multi-GeV accelerators, and present example electron beams from those experiments.
[1] R. Shalloo et al., Phys. Rev. E (2018)
[2] A. Picksley et al., Phys. Rev. E (2020)
[3] L. Feder et al., Phys. Rev. Research (2020)
[4] A. Picksley et al., Phys. Rev. Lett. (2023)
“Flying focus” techniques produce laser pulses with dynamic focal points that can travel distances much greater than a Rayleigh length. The implementation of these techniques in laser-based applications requires the design of optical configurations that can both extend the focal range and structure the radial group delay. This work describes a method for designing optical configurations that produce ultrashort flying focus pulses with arbitrary-trajectory focal points [1]. The method is illustrated by several examples that employ an axiparabola for extending the focal range and either a reflective echelon or a deformable mirror-spatial light modulator pair for structuring the radial group delay. The latter configuration enables rapid and automated exploration and optimization of flying foci, which could be ideal for experiments. This material is based upon work supported by the Department of Energy Office of Fusion Energy under Award Number DE-SC0021057 and by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0003856.
[1] M. V. Ambat, J. L. Shaw, J. J. Pigeon, K. G. Miller, T. T. Simpson, D. H. Froula, & J. P. Palastro, “Programmable-trajectory ultrafast flying focus pulses,” Opt. Exp., 31, 19 (2023).
Designs for linear colliders based on laser wakefield acceleration (LWFA) must address dephasing, which occurs when trapped particles outpace the accelerating phase of the wakefield. To address dephasing, current designs employ many stages, each operating at a low plasma density, which limits the acceleration gradient and elongates both the individual stages and total collider length. Here, we explore the possibility of a compact, continuously staged bubble-regime LWFA in high-density plasma by utilizing arbitrarily structed laser (ASTRL) pulses. By chaining together discrete pulses with controlled delays, powers, spot sizes, durations, polarizations, or focal positions, ASTRL pulses allow for the formation of a highly tunable flying focus that moves at the vacuum speed of light in plasma. In addition, the use of periodic density gaps mitigates distortion of the accelerating structure by dispelling depleted, red-shifted laser light. We present preliminary simulations using the OSIRIS-validated quasistatic particle-in-cell code QPAD for 800nm laser light at a plasma density of 3e18 cm^{-3}.
Laser Wakefield Acceleration (LWFA) offers a promising alternative to conventional accelerators, offering superior acceleration gradients. However, the effect of radiation reaction inside the wakefield can be detrimental to their operation. The transverse focusing field in the wakefield can drive betatron oscillations and cause radiation emission, with radiation back-reaction effects on the electron dynamics becoming stronger as the beam energy gradually increases during acceleration. As the beam energy exceeds 100 GeV, the radiation reaction behavior will deviate from the classical beavior and quantum radiation effects will cause a "stochastic heating," which can be an intrinsic beam energy spread mechanism for high-energy accelerators. The radiation can also dampen the transverse energy spread of the beam, causing radiative emittance reduction. Due to the dephasing and laser depletion, the operation of TeV class beam collider based on LWFA technology will require multiple LWFA stages, or using structured light as a driver. The coupling efficiency between two acceleration stages depends highly on the beam emittance and energy spread. Thus, understanding how radiation reaction effects influence the evolution of beam energy spread and emittance is an essential factor for constructing an LWFA-based TeV class beam collider. We also investigate the evolution of spin polarization in LWFA’s by employing our spin and polarized resolved QED module based on a particle-in-cell (PIC) code OSIRIS to predict the effect of radiation emission on the transport and acceleration of polarized beams.
This work is supported by the US National Science Foundation Award # 2108075.
Scaling laws for laser-plasma interactions can be expressed in various ways. One approach is to apply a transformation that leaves the governing equations invariant and ask how the overall system is modified, and treat technological limitations as a set of constraints. This talk will examine such transformations with particular attention to reductions in laser wavelength, with a view toward developing petawatt class excimer lasers. A petawatt argon fluoride laser facility, operating at a central wavelength of 193 nm, and based notionally on the Electra amplifier at the Naval Research Laboratory, will be sketched. Advantages of this short wavelength for both laser plasma acceleration and strong field QED will be discussed, based on scaling arguments, and particle-in-cell simulations.
Recently there has been significant interest in formulations of macro-particle models using variational methods. This is attractive because many of the inherent pathologies of traditional PIC methods are avoided. Broadly, there are two approaches to constructing these models that on the surface appear incompatible: a Lagrangian method based on the Low Lagrangian and a Hamiltonian method based on the noncanonical Vlasov--Maxwell Poisson bracket. In both cases, a reduction is performed on the distribution function, which is replaced by a finite sum of macro-particles with a fixed spatial structure and definite momentum. The distribution is thus replaced as dynamical variable by a collection of marco-particle positions and momenta. In the Lagrangian formulation, it is natural to represent the fields on a grid. Doing so yields an algorithm that is of the same computational cost as the traditional PIC algorithm but is free of grid-heating. It does not appear possible to introduce a grid for the field in the noncanonical formulation. Instead, a basis function expansion is used based on discrete exterior calculus. Here we resolve the apparent discrepancy between the two approaches and show that the noncanonical Hamiltonian formulation can be transformed into a canonical Hamiltonian system and careful treatment of the variational principle in both the Lagrangian and Hamiltonian settings is necessary to maintain charge conservation. In the Lagrangian setting, introducing a grid (which is required to be computationally performant) breaks gauge invariance leading to an unusual structure of the variational principle.
When an ultra-intense laser pulse propagates through a dense plasma, the front of the laser can be locally “etched” by the nonlinear laser-plasma interaction, forming an optical shock. The laser front edge becomes extremely sharp, reaching relativistic amplitude over a sub-wavelength scale. This gives rise to the Carrier-Envelope-Phase (CEP) effect in laser wakefield accelerators (LWFA), whereby an Expanding and Periodically Undulating Bubble (EPUB) is generated. The EPUB undergoes simultaneous expansion and periodic undulation according to the laser CEP and polarization. Particle-In-Cell simulations and analytic theory shows that EPUB gives rise to a phase and polarization dependent (PPD) plasma electron self-injection and acceleration, giving rise to spatiotemporally structured ultrashort (fs) high-charge (nC) high-current (tens to hundreds of kA) electron bunch. We discuss observables for this PPD process including electron and X-ray spectra and angular distribution. Experimental conditions necessary to observe these PPD processes in high-power laser facilities will be discussed, including plasma length and profile as well as laser power and duration. Methods to improve beam quality via magnets and apertures will be discussed, and specific examples relevant to the 100TW ultrashort laser facility in ELI-NP will be provided. This new regime of LWFA will provide a promising path to generating high-charge high-quality electron beams in many high-power laser facilities.
Laser plasma-based ion accelerators have not reached their full potential in producing high-radiation doses at high energies. The most stringent limitation is the lack of a suitable high-repetition rate target that also provides a high degree of control of the plasma conditions. For high-intensity laser-solid interactions, the absolute density and surface gradients of the target at the arrival of the ultrarelativistic peak is essential[1]. Accurate modeling of the leading edge-driven target preexpansion is required to strengthen the predictive power of computer simulations and thus to achieve higher beam energies. This calls for benchmark experiments with well-defined laser and plasma conditions.
In this talk, we report on high-repetition rate experiments in which cryogenic hydrogen jet targets are irradiated with intense laser pulses showing how such experiments open up new opportunities for understanding, improving and controlling the accelerator. The high-repetition rate is of interest not only for quasi-continuous acceleration, but also for addressing fundamental questions of the interaction. This cryogenic jet platform allows to experimentally benchmark simulations due to the large statistics. As two examples, we consider studies on the transition from an initial solid state to a plasma state[2], i.e. defining the starting point of subsequent target preexpansion and thus for modeling, and on expanding plasma density distributions[3], i.e. determining the plasma temperature evolution after laser irradiation as a comparison to simulations.
[1] M.Rehwald, et al. Nature Communications 14, 4009 (2023)
[2] C.Bernert, et al. Physical Review Applied 19, 014070 (2023)
[3] L.Yang, et al. Communications Physics 6, 368 (2023)
Ion acceleration via compact laser-plasma sources presents great potential for applications ranging from medical treatments to fusion research. Achieving the desired beam quality parameters necessitates an in-depth understanding and precise control of the laser-plasma interaction process. Our ongoing collaborative research at the DRACO PW (HZDR) and J-KAREN-P (KPSI) laser systems is focused on investigating the promising regime of Relativistically Induced Transparency (RIT).
In prior studies [1], we achieved high-performance proton beams (>60 MeV) in an expanded foil configuration, identifying an optimum at the onset of target transparency. Subsequent experiments recorded proton energies exceeding 100 MeV [2], emphasizing the critical role of the transparency onset time in optimizing beam parameters and enhancing process robustness. We utilize a combination of particle and laser diagnostics to explore the correlation between transparency onset and acceleration performance.
This contribution details our recent investigations into spectral components of transmission and emission from the laser-plasma interaction along the laser axis. Building upon established methodologies [3], our approach involves spectral interferometry, using the unperturbed laser beam as a reference, and correlates findings with proton acceleration performance. Our results indicate a promising direction for focused analysis of spectral and spatial light distribution, providing deeper insights into the complexities of laser-plasma interactions. They suggest multiple contributions to the transmission mechanisms, potentially involving a multi-shuttering process.
[1] Dover, N.P. et al.: Light Sci. Appl. (2023).
[2] Ziegler, T. et al.: Nat. Phys. (2024).
[3] Williamson, S.D.R. et al.: Phys. Rev. Appl. (2020).
For commonly used NIR drive lasers, the time, length and density scales pertinent to high-plasma-density LPA are difficult to access experimentally. However, as users of PIC codes will know, in fully ionized collisionless plasmas, the same physics happens at different temporal and spatial scales as long as these scales are adjusted in accord with the reference laser frequency. Therefore, a Long Wave InfraRed (LWIR) drive makes it much more feasible to visualize the plasma evolution in the laser ion accelerator using fast optical probing. We present two case studies where such experimental approach allows direct comparison between PIC simulations and actual observations.
For the first case, we discuss electron beam filamentation in an overcritical density plasma. Using shadowgraphy, we observe how fast electrons originated upon an LWIR laser absorption on a sharp density gradient propagate into the upstream plasma. Changing the probe timing allowed us to observe the plasma dynamics during and after the drive pulse. 2D PIC simulations agree with the observed change in the filament size and density with the plasma density.
For the second case, we explored the channeling of a high power laser pulse in a critical density plasma. By stacking together multiple shots we can stitch together the channel formation process. Again, the speed of channel formation predicted by PC simulations agrees well with the experiment.
And because of the scaling invariance, our findings might be applicable to NIR drives as well.
The interaction of an ultra-intense laser pulse with a near critical density target can result in the formation of a plasma channel, a strong azimuthal magnetic field and moving vortices. An application of this is the generation of energetic and collimated ion beams via Magnetic Vortex Acceleration (MVA). The optimized regime of MVA is becoming experimentally accessible with new high intensity laser beamlines coming online and advances made in near critical density target fabrication. A series of three-dimensional simulations was performed to study the robustness of the acceleration mechanism with realistic experimental conditions. Of particular interest is the acceleration performance with different laser temporal contrast conditions, in some cases leading to pre-expanded target profiles prior to the arrival of the main pulse. We studied the pre-plasma effects on the structure of the accelerating fields, transitioning from MVA into a bubble-like field structure at longer pre-plasma scale lengths, and performed a detailed analysis of the ion beam properties and the efficiency of the process. Additionally, we present improved scaling laws for the MVA mechanism when the focal spot size is taken into consideration.
This work was supported by the U.S. DOE-SC, FES, LaserNetUS, and HEP under contract number DE-AC02-05CH11231 and DARPA via Northrop Grumman Corporation. Computed using an ASCR Leadership Computing Challenge (ALCC) award at the Oak Ridge Leadership Computing Facility at the ORNL under contract number DE-AC05-00OR22725 and at the National Energy Research Scientific Computing Center, using award FES-ERCAP0027627.
Target normal sheath acceleration (TNSA) is one of the best-known laser-plasma interaction mechanism of ion acceleration, capable of generating multi-MeV collimated ion beams. The conventional TNSA (flat-foil target) has a few inherent limitations, such as poor coupling efficiency of the laser energy into hot electrons and short ion acceleration distance at the back of the target. By means of a 3D particle-in-cell simulations, we show that the interaction of ultra-intense ultrashort laser pulses with a periodic nano-trenched M-shaped Si structures [1] can produce highly collimated, energetic vacuum-accelerated [2] electron bunches in the nano-trench. This results in a substantial enhancement in both the total and cutoff energies of the produced Si ion beams. The numerical studies reveal the optimal laser-target parameters, such as nano-trench thickness, periodicity of structures, laser wavelengths and energies.
1) Shcherbakov, M.R., Sartorello, G., Zhang, S. et al. Nat Commun 14, 6688 (2023).
2) Jiang S. et al., Phys. Rev. Lett.,116, 085002 (2016); Naumova N. et. al., Phys. Rev. Lett., 93, 195003, 2004; Curtis A., Calvi C., Tinsley J. et al., Nat. Comm. 9, 1077 (2018).
The time for stationary plasma to recover its original state after a wake is excited determines repetition rate and luminosity of plasma-based colliders. Recent measurements at DESY [1] showed that an argon plasma of density ne ≈ $10^{16}$ cm$^{-3}$ in which a 0.5 J (0.5 nC, 1 GeV) e-bunch excited a first wake supported excitation of a second wake at the same location with indistinguishable beam properties within 60 ns. Here, we report Spring 2024 results of experiment E-324 at SLAC's FACET-II in which 20 J (2 nC, 10 GeV) e-bunches excited meter-long nonlinear wakes in stationary lithium, hydrogen, and argon plasmas of density ne ≈ $10^{16}$ cm$^{-3}$. Scattered light from a 1 mJ, 100 fs optical pulse impinging on the plasma filament at grazing incidence (~1˚) at delays 1 ns ≤ ∆t ≲ 1 ms then sensitively probed wakefield remnants. In lithium plasma, probe scatter peaked at ∆t ≈ 100 ns and remained visible out to ∆t ≈ 2 microseconds. In contrast, no scattering was visible from the e-beam-excited hydrogen plasma beyond ∆t ≈ 100 ns; scattering from Argon disappeared at ∆t ≈ 300 ns. The results will be discussed in light of earlier findings of experiment E-224 [2], which showed that ion motion dominated energy transport out of the beam-excited region for ∆t ≳ 0.3 ns.
References:
[1] R. D’Arcy et al., Nature 603, 58-62 (2022).
[2] R. Zgadzaj et al., Nat Commun 11, 4753 (2020).
FLASHForward is a beam-driven plasma-wakefield accelerator (PWFA) experiment at DESY, acting as a test bench to develop technologies to accelerate electron beams with high quality and high average power. By enhancing conventional acceleration methods with plasma acceleration, the cost and footprint of future accelerators could be significantly reduced. To achieve this, it is crucial to have detailed knowledge of plasma dynamics, both spatially and temporally, in the plasma accelerator stage. FLASHForward utilises discharge capillary plasma sources. An in-house hydrodynamic plasma model was used to simulate these sources. Simulated plasma density profiles are then input into particle-in-cell (PIC) codes to simulate beam-plasma interaction. In this contribution, such simulations are compared to experimental measurements of electron bunch deceleration to provide insight into transverse plasma density redistribution at microsecond timescales.
The acceleration of positron beams in plasma wakefield accelerators (PWFA) has gained significant interest in recent years due to its potential applications in colliders. One promising scheme for achieving positron acceleration in PWFA is to create an electron-driven blowout wake within a finite-radius, pre-ionized plasma column (narrow plasma column). This approach allows for the formation of an elongated region of sheath electrons at the closing of the first wake period, which can accelerate positrons while simultaneously providing a transverse focusing force. We describe the acceleration technique and present initial results from the E333 experiment at the Facility for Advanced Accelerator Experimental Tests II (FACET-II), which in its first phase investigates the behavior of PWFA in a narrow plasma column with a single electron driver. Our simulations show that the transverse focusing force of the wake is asymmetric when the driving electron beam offsets from the center of the narrow plasma column. This asymmetric transverse force guides the electron beam along the plasma column trajectory. We report preliminary experimental evidence of the guided electron beam in a narrow column PWFA and a reduction in energy loss with respect to PWFA in a wide plasma column.
Beam-driven plasma wakefield acceleration can sustain accelerating fields on
the GV/m scale, making it well-suited for linear collider applications. However,
in recent years, an efficiency-instability relation has been proposed, which limits
the energy transfer efficiency from the wake to the trailing bunch that can be achieved
without inducing transverse instabilities detrimental to the transverse phase
space of the accelerated bunch. We discuss the efficiency-instability relation for
a transversely misaligned trailing bunch and a novel method that can be used to
identify the beam-breakup instability (BBU) on a dispersive dipole spectrometer
and quantify the size of the instability. We show preliminary results using data
from the E300 experiment at the FACET-II facility, showcasing the use of this
method.
The thin, underdense, passive plasma lens promises compact, strong, tunable, axisymmetric focusing of intense electron beams. It is ideally suited for matching beams into and out of plasma wakefield accelerator stages, and for reducing divergence of high-brightness plasma-injected beams as they exit the plasma source. The plasma lens comprises a sub-millimeter scale, laser-ionized plasma in the outflow of a supersonic gas jet. Preliminary results from recent experiments at FACET-II using a laser-ionized passive plasma lens will be presented showing strong focusing of a 10 GeV electron beam.
Development of the corrugated waveguide-based colinear wakefield accelerator at Argonne National Laboratory (ANL) for a compact hard x-ray free-electron laser (FEL) facility has passed a milestone with the demonstration of most principal accelerator and FEL components: a 30 cm long strong-back structure to hold and cool the corrugated waveguide, sub-terahertz frequency electromagnetic couplers for extraction of the fundamental mode power and beam offset diagnostic, high field gradient quadrupoles for beam guidance and suppression of a beam breakup instability, small gap force neutral adjustable phase undulator (FNAPU). All structures and couplers have been tested in the microwave laboratory at ANL and with the electron beam at the Brookhaven National Laboratory’s Accelerator Test Facility. The quadrupoles and a prototype of the quadrupole “wiggler” have been characterized via magnetic measurements. A FNAPU’s prototype was fabricated and characterized. In all cases, a good agreement with design parameters has been demonstrated.
The global collaboration between PAL, NIU, ANL, and KU is ongoing to develop an electron beam-driven THz power generation and two-beam acceleration in SWFA. We successfully demonstrated the fabrication of a 0.2 THz structure and the characteristic of wakefield using the beam-based experimental measurement. of a 0.2 THz structure a few years ago. The success of a new fabrication method led us to the next step, high-power generation. Currently, we aim to demonstrate the extraction of RF power with its peak of >1 GW from a 0.4 THz structure.
The RF power generated from the 0.4 THz structure designed is expected to reach a peak power of 3.3 GW and an average power of 1.5 GW (averaged over a single pulse) by using a bunch train with 16 bunches, each with a charge of 1 nC as a drive beam.
We present the current status of R&D towards high-power demonstration, including future plans.
We present a previously unobserved effect arising from the interaction between a “flat” electron beam and a planar-symmetric dielectric structure. For a beam injected with an angle between the primary transverse axis and the dielectric surface we observe a skew-quadrupole-like short-range wakefield interaction. We do not observe this skew effect for beams injected parallel to the dielectric. We use a multipole field fitting algorithm to reconstruct the projected transverse wakefields from our experimental results. We employ a simple two-particle model to provide insight from theory. We compare our experimental results to those generated by particle in cell simulations.
This paper presents the final physics design of the THz wakefield acceleration experiment using three dielectric structure cross-sections at the Argonne Wakefield Accelerator (AWA) facility. The experiment will focus on multi-bunch excitation of wakefields, exploration of the wakefield transverse-force topology, and possibly support an experiment on energy recovery. This contribution discusses start-to-end simulations of the experiment and expected experimental signature. We specifically address the resolution requirements on the beam diagnostics and the design of a THz-radiation collection system.
Structure-based wakefield accelerators (SWFA) promise orders of magnitude improvements in accelerating gradient over conventional approaches and have been identified as a candidate technology for future applications ranging from compact free electron lasers to multi-TeV lepton colliders. However, achieving the desired beam energy and quality can require meter-scale structures with tight tolerances, introducing new constraints on structure and beam characteristics to minimize emittance growth and combat transverse instabilities. High fidelity and self-consistent simulations of high brightness beams over these lengths necessitate enormous computational resources, making parametric studies of novel structures or instability-mitigation schemes unfeasible with standard practices. We present a technique for decomposing high dimensional wakefield systems into a set of lower dimensional components, capable of accurately reconstructing the structure response in a fraction of the time. We discuss the approach and implementation of this technique using Green’s Functions for common structure geometries. We demonstrate the potential for significant reduction in computation times and memory footprint using such representations. Finally, we discuss prospective extensions of this technique to higher dimensions, and explore the use of machine learning in generating these representations for novel structure geometries.
A comparative analysis of two types of dielectric laser accelerators (DLA) based on periodic (grating) and flat dielectric structures to accelerate electrons in the energy range from 300 KEV to 3 GEV is presented. The main attention is paid to the conditions, efficiency and restrictions of each acceleration method, as well as the influence of laser radiation parameters on electron acceleration processes. Single and double (both grating and flat) dielectric structures and their impact on acceleration are considered.
For the study of two types of quartz DLA, the TI:SA laser system with a generation band width 790-810nm (FWHM), the laser electric field 6 GeV/m. The study showed that a flat dielectric structure provides more effective acceleration in a wide range of energies, especially with a symmetrical geometry (double structures), compared with the periodic structure. If we consider only a periodic structure, then with the selected symmetrical geometry, for the ultra of relativistic electrons, it demonstrates the acceleration rate two times of magnitude more than for single configuration. However, the use of a one-sided periodic structure turns out to be preferable for accelerating electrons with moderate energies, ~0.5-0.9 MeV, where the acceleration rate in a one-sided configuration is higher than in a symmetric (double) periodic structure.
The space-time distributions of laser-excited electromagnetic fields in the accelerating channel and their influence on the electron beam is analyzed also. The advantage of a flat structure over a periodic one, which arises due to the design features of the corresponding dielectric accelerators, is discussed.
This study presents a Dielectric Laser Accelerator (DLA) tailored for single-electron acceleration, optimised for particle survival and minimal beam energy spread. Leveraging a genetic algorithm, we strategically design the dielectric structure to achieve efficiency in both computational runtime and structure performance.
The study focuses on three key aspects: the selection of a suitable electron source with the right emittance, beam dynamics for sub-relativistic and relativistic electrons, and the alignment of beam properties with the requirements for indirect dark matter search. Our findings establish DLA as a promising tool for advancing dark matter research.
Indirect dark matter exploration necessitates a high repetition rate of single electrons in the GeV energy range. The DLA's potential to operate at GHz rates makes it an ideal candidate for designing a compact accelerator for dark matter search. To achieve high repetition rates, a suitable laser and electron source are essential. Hence, we introduce RF-based electron microscope type-sources for our design, as they can operate at 3GHz or higher.
A segmented optimization approach is employed to the structure accelerating particles from 10 MeV to 1GeV. Instead of conducting global optimization for the entire DLA structure length, we will employ a localized optimization strategy, optimizing each 10mm-long segment independently while iteratively adjusting the input beam conditions for subsequent segments. Through this iterative process, the DLA structure can be optimized in an efficient runtime. The output beam parameters like energy spread and survival rate will be compared to the parameters required for indirect search of dark matter.
Next generation laser drivers for laser plasma acceleration and secondary radiation sources will require 3 to 4 orders of magnitude increase in pulse repetition rates, to produce TW-PW class peak power ultrashort pulses at multi-kilowatt average powers [1]. Coherently combined ultrashort pulse fiber laser systems are recognized as a pathway to such high power technology [1]. However, although the current state-of-the-art high-power coherently combined fiber laser systems have demonstrated a relatively large number of combined channels ranging from 16 and up to 61 so far, but they all achieved only moderate femtosecond pulse energies in the 10-30mJ range, far below what is needed for driving particle-acceleration experiments.
We had developed a novel time-domain coherent combining technique (coherent pulse stacking amplification - CPSA) that enables 100 times higher energies per channel than conventional fiber CPA, achieving record high femtosecond pulse energies of up to ~10mJ per channel, far exceeding any other fiber laser results. This opens an effective pathway to reaching higher pulse energies, which we recently validated in a 4-channel coherently-spatially combined array, producing ~27mJ per spatially and temporally combined beam [2]. We will report the development of a 12-channel table-top laboratory system upgrade to produce 100mJ/1kW spatially and temporally combined beams, which after compression are sufficient for acceleration and secondary-radiation experiments. This work includes development of a new energy-scalable pre-pulse cleaning technique necessary for driving majority of high-intensity laser plasma interactions. This development constitutes an important milestone towards future multi-kW average and TW-kW peak power laser drivers.
Compact laser plasma accelerators running at repetition rates >1 kHz promise a wide range of applications in science research, medicine, and security. Commercially available laser systems operating at kHz repetition rates offer mJ pulses with pulse duration as low as tens fs. To fulfill the resonant condition for the laser wakefield acceleration, temporal compression of these pulses is necessary. We report on nonlinear compression of a commercial Ti:Sapphire laser from ~40 fs to <4 fs in a hollow-core fiber compressor with 60% overall efficiency. We show that controlling the nonlinearity prior to coupling into the fiber proves to be critical to achieve high energy transmission. Through third order dispersion tuning, the peak power above 1 TW was achieved, which is suitable for driving a MeV-level laser plasma accelerator.
This work was supported by the DOE under Contract No. DE-AC02–05CH11231, and by NNSA.
Lasers capable of generating petawatt-class peak powers at kHz repetition rates are needed for future laser wakefield accelerators (LWFAs) and could have far reaching impacts in industry, medicine and national security. We present the development of Tm:YLF laser technology including joule-level short pulse amplification and gas-cooling at high average power in two separate experiments. We show chirped pulse amplification (CPA) producing stretched broadband pulses up to 1.59J pulse energy centered at 1.88um and subsequent compression to sub-300fs pulses which demonstrates Tm:YLF’s short pulse amplification capability. Shorter, sub-150fs, pulse compression may be possible by addressing gain narrowing. We also show heat removal surpassing 20 W/cm^2 from a diode-pumped, gas-cooled slab which demonstrates Tm:YLF’s average power capability. These results represent an order of magnitude higher heat extraction than any laser material currently employed in petawatt-class systems to-date, showing that a gas-cooled amplifier head geometry supports multi-kW operation. These results along show the potential suitability of Tm:YLF based lasers for drivers of future laser plasma acceleration, including specifically for LWFA drivers.
Prepared by LLNL under Contract DE-AC52-07NA27344, LLNL-ABS-865686. This work was supported by the Department of Energy Office of Science ARDAP Accelerator Stewardship Program now part of the HEP Program, Project No. SCW1648, the LLNL LDRD program under Project numbers 21-ERD-016 and 19-DR-009 and by the Defense Advanced Research Projects Agency (DARPA) under the Muons for Science and Security (MuS2) program.
The laser pulse properties required for a future laser-driven collider are routinely demonstrated with Hz class Ti:Sa lasers; however, a four orders of magnitude increase in repetition rate will be necessary to meet collider luminosity specifications [1]. We model thermal effects in Ti:Sa amplifiers, including thermal effects at high repetition rate, using an operator splitting approach that divides each crystal and the laser pulse into slices [2]. Each laser slice is represented by a monochromatic 2D wavefront, with intrinsic bandwidth captured via overlapping slices. The 1D Frantz-Nodvik equation accurately captures amplification on a cell-by-cell basis within a 2D Cartesian mesh. Thermal lensing uses a near-axis expansion. Simulations show good agreement with experimental data, including the redshift during amplification. We will review the Sirepo-Silas app for executing these simulations in your browser [3]. Alternative simulation approaches will be reviewed, and future directions will be discussed.
[1] L. Kiani et al, “High average power ultrafast laser technologies for driving future advanced accelerators,” JINST 18, T08006 (2023).
[2] D.L. Bruhwiler et al., “Thermal modeling and benchmarking of crystalline laser amplifiers,” in Proc. Int. Part. Accel. Conf., THPOTK062 (2022).
[3] The Sirepo-Silas app, https://www.sirepo.com/en/apps/lasers/
Precise control of the temporal shape of ultrashort pulses of terawatt scale peak power is often desirable in experiments. In previous work, we used single, few-cycle 5 fs pulses for 1 kHz rep. rate laser wakefield acceleration (LWFA) to 15 MeV in near-critical density hydrogen plasma [1]. Double pulses are also of interest for LWFA, as prior simulation studies suggest that resonant driving of wakes enhances injection and acceleration [2]. However, prior methods for generating double few-cycle pulses exhibit energy loss of up to 80% [3]. Our method [4] utilizes precise control of oscillator seed pulses before chirped pulse amplification. Pulse peak separations as short as 10 fs (~4 cycles) are generated [4]. We present the double pulse generation scheme, particle-in-cell simulations suggesting that the interaction of these pulses in plasma can tunably modify and enhance electron acceleration and injection, and preliminary experimental results.
[1] F. Salehi et al., Phys. Rev. X 11, 021055 (2021).
[2] C. Kim et al., Phys. Lett. A 370, 310 (2007)
[3] A. Catanese et al., OSA Contin. 4, 3176 (2021).
[4] L. M. Railing et al., Opt. Lett. 49, 1433-1436 (2024)
The advanced accelerator community increasingly recognizes the importance of extending high peak- and average-power laser facilities to longer wavelengths. This recognition is driven by the lambda-squared scaling of the ponderomotive force, inverse-lambda-squared scaling of critical plasma density, and linear-lambda scaling of the number of photons per joule of energy. A significant potential application of long-wave infrared (L-WIR) lasers is in laser wakefield acceleration (LWFA), where achieving an efficient "bubble" acceleration regime is expected at pulse durations below 1 ps and peak powers exceeding 10 TW.
Currently, picosecond pulse amplification in high-pressure-gas CO2 amplifiers is the only method capable of generating L-WIR pulses with terawatt energies and beyond. Nevertheless, emerging mid- and long-wave infrared (M/L-WIR) solid-state laser technologies are essential for providing the necessary infrastructure for next-generation systems. For instance, multi-millijoule solid-state seed lasers can enable the generation of ~500 fs multi-joule pulses at the output of chirped-pulse amplification-based CO2 amplifiers. Additionally, high-energy lasers at 2.8 µm are required for the efficient pumping of CO2 amplifiers at high repetition rates.
In this talk, we present an overview of the current state of L-WIR lasers relevant to LWFA, emphasizing the latest trends in the development of supporting M/L-WIR laser systems and their components. This includes advancements in multi-millijoule seed lasers and high-energy pump lasers, which are critical for achieving the next generation of high-power, high-repetition-rate laser systems. These developments are crucial for enabling new capabilities and enhancing the performance of LWFA, driving progress in the field of advanced accelerators.
The AWAKE experiment at CERN explores accelerating electrons using proton-driven plasma wakefields. A crucial challenge is creating long (10-100 meters), highly uniform plasmas with electron densities in the range of 1 to 10 x 10$^{14}$ cm$^{-3}$. This presentation describes the first experimental test of a 10-meter discharge plasma source (DPS) in the AWAKE experiment.
The DPS uses a double-pulse direct-current discharge in noble gases (He, Ar, Xe) and its shot-to-shot reproducibility was investigated across a wide range of pressures (8-45 Pa) and currents (300-600 A). The plasma density was characterized using longitudinal interferometry over hundreds of shots.
The DPS’s applicability and readiness were assessed in the AWAKE experiment by propagating the 400 GeV proton bunch through the plasma and observing the development of the self-modulation instability (SMI). The measured SMI frequency corroborated the plasma density values obtained through interferometry. These results demonstrate the DPS's potential for use in AWAKE and pave the way for future studies on achieving the critical 0.25% longitudinal density uniformity needed for electron acceleration.
Filamentation instability can occur in plasma wakefield accelerators as well as in astrophysical media. This instability takes place when a charged particle bunch streams through a plasma with skin depth smaller than the bunch transverse size, so that the plasma return current flows within the bunch. Repulsion between opposite currents tends to reinforce any initial transverse perturbation or anisotropy in the current density profiles, causing the instability to grow, transforming the bunch into multiple high-current-density transverse filaments.
Occurrence of filamentation generates magnetic fields, by converting part of the kinetic energy stored in the bunch into magnetic energy. This process is one of the plausible candidates for magnetization of astrophysical media, as well as for the magnetic fields enhancement that could explain phenomena such as long-duration afterglow of gamma-ray bursts and collisionless shocks.
At the AWAKE experiment at CERN, we observed the early stage of filamentation (predicted by theory to occur in the form of the oblique instability) of a relativistic, wide proton bunch traveling in plasma [1], and we estimated the amplitude of the magnetic field that it generated. We discuss the implications for the design of a plasma wakefield accelerator.
[1] L. Verra et al. (AWAKE Collaboration), Phys. Rev. E 109, 055203 (2024)
To suppress the BBU instability and improve characteristics of accelerated bunches in Dielectric Wakefield Accelerator one can be used the plasma filling of the transport channel*.
Here we present the results of analytical and numerical studies of the dynamics of accelerated electron/positron and drive electron bunches under wake acceleration in a plasma DWA with a vacuum channel. The wake field is excited by an electron bunch in a quartz dielectric tube inserted into a cylindrical metal waveguide. The inner region of the dielectric tube is filled with plasma with a vacuum channel along the waveguide axis. At numerical simulations the energy and spatial characteristics, acceleration efficiency, emittance, and energy spread for positron and electron bunches is studied for different radii of the vacuum channel and two models of the plasma density dependence on the radius: a homogeneous and an inhomogeneous dependence characteristic of a capillary discharge.
The analytical studies have discovered the presence of two surface eigenwaves, which is absent in corresponding dielectric-loaded waveguide without plasma filling. The main contribution to amplitude of transverse wakefield, responsible for focusing of accelerated electron or positron bunches, brings the backward plasma surface eigenwave. The comparative analysis of the data resulting from analytical studies and the ones obtained by numerical simulation has demonstrated qualitative agreement between the results.
* G.V. Sotnikov, et al., Nucl. Instr. and Meth. in Phys. Res., A740, 124 (2014).
A wakefield experiment that will utilize electron beams with highly asymmetric transverse emittances, or flat beams, to drive plasma wakefields is underway at the Argonne Wakefield Accelerator (AWA) facility . In the underdense regime, the flat beams create an elliptical blowout structure, resulting in asymmetric focusing forces in the transverse planes. The beam evolution and matching conditions within the elliptical blowout are presented. The results are used as the foundation for a novel experiment that uses a compact, 8-cm long, capillary discharge plasma source developed at UCLA. The plasma source is capable of generating plasmas with particle densities in the range of 1014-1016 cm-3 . The main facets of the program include analytic representations of the blowout ellipticity and matching conditions, supported by particle-in-cell simulations for the beam-plasma interaction. Detailed engineering preparations for the experiment at the AWA are also presented including a differential pumping installation to preclude the use of plasma-isolation windows that would have deleterious effects on beam emittance during transport. Diagnostics for both beam properties, and plasma wakefield effects in transverse and longitudinal dimensions are included.
An electron source is a crucial component of any accelerator facility, as it defines the scientific reach and capabilities of accelerator applications. Therefore, detailed modeling of electron emission along with advanced growth and characterization of cathode materials are required to enhance emission capabilities of cathodes. This presentation will review the practices being developed at Northern Illinois University (NIU) towards improving quality of conventional photocathodes and exploring novel electron sources that can outperform those currently used at leading accelerator facilities. Specifically, we will discuss Monte Carlo modeling of spin-polarized photoemission from GaAs photocathodes and potential novel spin-polarized electron sources. Additionally, we will review the main mechanisms limiting beam brightness and the requirements for developing high-quality alkali antimonide photocathodes.
A novel X-band (11.7 GHz) photoemission gun (Xgun), powered by short RF pulses (9 ns), has demonstrated unprecedented surface electric fields of approximately 400 MV/m on the photocathode. As a first step towards fully understanding the Xgun’s performance in the high-field regime, we focused on the fundamentals of photoemissions, including the impact of the Schottky effect, multipacting, and dark current emission. The characterization and benchmarking of electron emission for photocathode fields ranging from 60 MV/m to 320 MV/m are discussed. Additionally, we apply these simulations to the next-generation XRF gun being designed.
Plasma based acceleration is considered a promising concept for the next generation of linear electron-positron colliders. Despite the great progress achieved over the last twenty years in laser technology, laser- and beam-driven particle acceleration, and special target availability, positron acceleration remains significantly underdeveloped if compared to electron acceleration. This is due to both the specifics of the plasma-based acceleration, and the lack of adequate positron sources tailored for the subsequent plasma based acceleration. Here a positron source based on the collision of a high energy electron beam with a high intensity laser pulse is proposed. The source relies on the subsequent multi-photon Compton and Breit-Wheeleer processes to generate an electron-positron pair out of a high energy photon emitted by an electron. Due to the strong dependence of the Breit-Wheeler process rate on photon energy and field strength, positrons are created with low divergence in a small volume around the peak of the laser pulse. It is shown that further reduction of the divergence can be achieved by employing frequency doubled and quadrupled laser pulses. The resulting low emittance in the submicron range potentially makes such positron source interesting for collider applications.
This research was supported by LDRD funding from LBNL provided by the Director and the U.S. DOE Office of Science Offices of HEP and FES (through LaserNetUS) under Contract No. DE-AC02-05CH11231, and used the computational facilities at the National Energy Research Scientific Computing Center (NERSC).
Muons and their applications in tomography of large objects have recently gained significant interest within the accelerator physics community. However, the lack of portable muon sources has limited muon tomography to relying on cosmic rays, which have a typical flux of $F~1 s^-1 cm^-2$ at ground level for muon energies above 1 GeV. This low flux restricts muon tomography to objects that remain immobile for extended periods. Laser-Plasma Accelerators (LPAs) have demonstrated production of multi-GeV-class electron beams over compact accelerating lengths. When a converter target is placed in front of the generated electron beam, a substantial number of muon pairs are produced via the Bethe-Heitler process. Therefore, an LPA can serve as a viable, compact, and transportable high-flux muon source. In this talk, we present recent experimental results at the BELLA Center, where muon production from LPA-produced, multi-GeV electron beams was demonstrated. Simulations show that the interaction of the beam with the layers of lead contained in the electron beam dump produce a collimated cone of muon pairs, which were detected on the other side of the wall using scintillating paddles and pixelated silicon detectors.
This work was supported by DARPA. This work was also supported by the Director, Office of Science, Office of High Energy Physics, of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231, and used the computational facilities at the National Energy Research Scientific Computing Center (NERSC).
The characterization and mitigation of collective beam effects, particular coherent synchrotron radiation (CSR), represents an important challenge in facilitating the development of particle accelerators with higher beam brightness. Among the mitigation strategies proposed in the literature, the use of appropriately configured shielding walls to curb CSR remains an promising area of research with several open problems. In this work, we consider the construction of a simulation method based on the use of an effective Green's function for such systems. Utilizing such an approach would allow for characterizing the emitted radiation in a manner that (1) is mesh independent, therefore eliminating the numerical dispersion errors present in traditional PIC methods and (2) accounts for the effects of shielding walls. We will discuss the theoretical components involved in constructing the Green's function, along with an analysis of the computational cost compared to existing image current methods in the literature. This work is part of a broader project that involves a planned sequence experiments at the Argonne Wakefield Accelerator (AWA) that aims to probe CSR effects (including shielding) over a wide range of parameters. The results of these experiments will eventually be used to benchmark the proposed simulation tools for complex bunch shapes and shielding configurations.
This research was supported by the U.S. Department of Energy, Office of Science, Office of High Energy Physics under Award DE-SC0024445.
Free-electron laser facilities demand versatile and inexpensive THz sources for pump-probe experiments. Smith-Purcell radiation provides a compact method to generate resonant and narrowband terahertz sources when relativistic electrons go through periodic dielectric grating structures, which are cost-efficient when fabricated by 3D printing. It has certain advantages over other available approaches but is limited by its low radiation power. This work proposes a 3D terahertz emission-collection concept to boost the terahertz efficiency and narrow the bandwidth of the central wavelength. Systematic simulations demonstrate that the 3D Smith-Purcell radiation can improve the coherent radiation power by orders of magnitude compared with the conventional 2D collection concept. Most importantly, mechanical deformations are first proposed to be introduced to deformable dielectric materials to generate continuously tunable THz radiations from ultrarelativistic electrons. A high-energy terahertz radiator, based on a helix pillar structure from inverse design optimization, is verified to emit more powerful terahertz radiation and achieve considerable tunability upon mechanical loads. This work provides valuable insights into the development of high-power and tunable narrowband terahertz radiators.
A laser pulse composed of a fundamental and an appropriately phased second harmonic can drive a time-dependent current of photoionized electrons that generates broadband THz radiation. Over the propagation distances relevant to many experiments, dispersion causes the relative phase between the harmonics to evolve. This “dephasing” slows the accumulation of THz energy and results in a multi-cycle THz pulse with significant angular dispersion. Here, we introduce a novel optical configuration that compensates the relative phase evolution, allowing for the formation of a half-cycle THz pulse with almost no angular dispersion. The configuration uses the spherical aberration of an axilens to map a prescribed radial phase variation in the near field to a desired longitudinal phase variation in the far field. Simulations that combine this configuration with an ultrashort flying focus demonstrate the formation of a half-cycle THz pulse with a controlled emission angle and 1/4 the angular divergence of the multi-cycle pulse created by a conventional optical configuration.
This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0004144 and the Office of Science under Award Number DE-SC0021057.
We present experimental results from Helmholtz-Zentrum Dresden-Rossendorf of a THz Smith-Purcell Radiation source generated using Laser Wakefield Accelerator electron bunches. Affordable and small, aluminum-coated gratings were placed near accelerated electron bunches with an average energy and charge of 405 MeV and 467 pC to produce strong, coherent emission. The generated shots of radiation were transmitted through a high-pass filter, and had significant enough energy to be observable on a Pyrocam IV pyroelectric detector. Initial analysis suggest energy per shot within the 10s-100s uJ range, with peak electric fields as large as 0.66 MV/cm incident on the detector. Furthermore, the known exponential dependence of Smith-Purcell Radiation for a pencil electron beam as a function of distance from the source (grating) was modified due to the transverse size and shape of the electron bunch, and could be explained using a 1D model.
Multi-mJ terahertz (THz) radiation was generated in the process of laser wakefield acceleration (LWFA) when a gas jet was irradiated by 100-TW-class laser pulses [1]. The emitted THz radiation is radially polarized and broadband with an energy conversion efficiency of 0.15%. The amount of energy is orders of magnitude larger than expected from the coherent transition radiation (CTR) model, in which a relativistic electron bunch produced in LWFA emits coherent THz radiation when it exits the plasma-vacuum boundary. The correlation between the electron beam properties (energy and charge) and THz output energy shows that high-energy (>150 MeV) electrons do not necessarily yield high-power terahertz radiation. Instead, low-energy (<MeV) but high-charge electrons can produce much stronger terahertz radiation. To explain such results, a coherent radiation (CR) model is proposed—the electrons accelerated by the laser ponderomotive force and subsequent plasma wakefields radiate broadband emission continuously along the laser propagation direction, resulting in phase-matched conical THz radiation in the far field [1]. A particle-in-cell (PIC) simulation also shows that the wakefields are highly nonlinear and the spatiotemporal structure decays on the time scale of picosecond, generating coherent THz radiation throughout the propagation [2]. Recently, a multi-petawatt laser was used to produce high-energy (tens of mJ) THz radiation, together with multi-GeV electron beams.
[1] T. Park et al., “Multi-millijoule terahertz emission from laser-wakefield-accelerated electrons,” Light Sci. Appl. 12 37 (2023).
[2] M. Rezaei-Pandari et al., “ Investigation of terahertz radiation generation from laser-wakefield acceleration,” AIP Advances 14, 025347 (2024).
Cyclotron Resonance Accelerator has several attractive features including: a compact robust room-temperature single-cell RF cavity as the accelerator structure; continuous high current accelerated dc beam output with self-scanning, obviating need for a separate beam scanner.
An electron accelerator version, electron Cyclotron Resonance Accelerator (eCRA) [1], is under the development to be highly compact and efficient to produce high power electron beams and x-ray beams for medical, research, sterilization, and national security applications, so as to replace radioactive materials. Progress on the eCRA development, including numerical simulation, engineering design, and on-going experimental efforts will be reported here.
And an deuteron accelerator version, the deuteron Cyclotron Auto-Resonance Accelerator (dCARA) is presented here as well. Simulations predict that dCARA will produce a high-current multi-MeV beam of accelerated deuterons which could be highly competitive with that produced either with linacs or cyclotrons for an application to produce, via deuteron stripping, a high flux of neutrons with an energy spectrum centered near 14.1 MeV, as needed for testing inner-wall materials for a future deuterium-tritium fusion power reactor.
Acknowledgement: Support from U.S. Department of Energy and Brookhaven National Laboratory is acknowledged.
References:
[1] Shchelkunov, S. V. and Chang, X. and Hirshfield, J. L., 2022, Compact cyclotron resonance high-power accelerator for electrons, Phys. Rev. Accel. Beams, 25.021301, American Physical Society.
In the context of building a compact Inverse Compton Scattering X-ray source, an Yb:YAG laser was used to generate both the electron emission from a photocathode and act as the interaction laser on a 100 MeV inverse Compton scattering experiment. The laser generates 25 mJ pulses at 1030 nm, 1.5 ps long, up to 120 Hz. 10 % of the energy is sent into a Fourth Harmonic Generation (FHG) module where frequency doubling happens twice. Up to 200 µJ of adjustable Ultra-Violet (UV) laser can be exploited and sent towards the photocathode. The rest of the energy, 90 % of the initial IR beam, is propagated to the interaction region. The goal is to match a 1 mm beam diameter (flat-top) on the photocathode and 40 µm (1/e2) at the interaction region with high stability. To reach it, significant effort was put into optimization using state of the art laser propagation software and various tools like low aberrations lenses, truncated Gaussian beam, vacuum transport, relay of images, and closed loop stabilization system. In the end, this project pairs strong optical and mechanical constraints. A significant part of it was built and commissioned, showing exciting results. We will show the whole laser system together with the various steps to reach the accelerator’s needs, and the current achievements.
The successful operation of future e+ e- linear colliders (LC) critically relies on the ability to tightly focus beams at the interaction point to achieve high luminosities. With spot sizes expected to reach the nanometer scale in TeV LC, traditional beam delivery systems face challenges due to chromatic effects and the requirement of small emittance. To overcome these challenges, the concept of adiabatic plasma lenses for the electron arm of the collider has emerged as a potential solution. In an azimuthally symmetric passive adiabatic plasma lens, a plasma wave wake is excited by a particle beam and a trailing beam surfs on the wake, experiencing a linear focusing force of mω2pr/2, which is proportional to the plasma density. An adiabatic plasma upramp is designed so that the focusing force on the trailing beam slowly increases during propagation. However, the tightly focused beam of LC can induce ion motion within the beam, an aspect that has not been extensively investigated in previous studies of adiabatic lenses. We propose designs of adiabatic plasma lens for final focus of the electron arm of 2TeV-15TeV COM LC using the advanced simulation tools, QuickPIC with adaptive mesh refinement and QPAD. Furthermore, we show that ion motion on the trailing beam will increase the strength of the focusing force, which can relax the stringent emittance requirements for the LC design. Additionally, we examine how an asymmetric drive beam can add asymmetry to the witness beam, thereby possibly reducing beamstrahlung during e-e- or e+e- collision.
Attosecond bunch generation may play a key role in many scientific applications, such as providing high temporal resolution for ultra-fast electron diffraction and mitigating beam-beam effects in linear colliders. Recently, we have started studying the feasibility of generating an attosecond bunch and its high-resolution measurement using the existing Argonne Wakefield Accelerator(AWA) facility to understand its dynamics and challenges. Currently, both ballistic bunching and c-type chicane are not available at the AWA facility. Thus, we have adopted a slightly different version of a chicane compressor, which is called a reversed chicane, for the experimental study without impacting the existing beamline. We have designed the reversed chicane for the AWA facility and confirmed its capability of bunch compression using simulations. Further simulation studies have been carried out to confirm the feasibility of experimental demonstration of attosecond bunch generation. Simulations have been done using ASTRA for the injector and ELEGANT for the reversed chicane. We present preliminary simulation results.
A novel diagnostic based on the well-established electro-optic sampling (EOS) technique is adaptable for non-interceptive, ultrafast position monitoring for high-intensity femtosecond beams. By using two pairs of crystals, the EOS system can also reveal the e-beam’s transverse position with ultrafast temporal resolution. This configuration is informally called the electro-optic sampling beam position monitor (EOS-BPM). In comprehensive application, the EOS-BPM can yield the full 3D centroid positioning of two bunches in a wakefield accelerator, or the tilt of a beam used to power a light source. Under ideal conditions, simulation-based estimates show that this device may be able to achieve temporal and transverse resolution for the beam centroid positions of a two-bunch wakefield accelerator beam of order 50 fs and 1 μm, respectively. An initial prototype of the EOS-BPM using only 1 pair of crystals, called 2D EOS-BPM has already been conceptually developed and is currently installed at the SLAC FACET-II facility. We improved its design and showed efficiency and reliability of our optimization by running benchtop tests. We also designed a prototype EOS-BPM using 2 pairs of crystals and extended our work to build a first version of it, proving its mechanical and optical functionality.
Structure-based wakefield acceleration (SWFA) is a proposed concept to overcome limitations in conventional accelerators. This approach allows for the creation of short-input radiofrequency (rf) pulses, which have been empirically shown to reduce breakdown rates at a given gradient. Metamaterial structures with negative group velocity have shown promise in accelerator applications. A structure wakefield experiment, with a metamaterial accelerator, exploited the direct benefits of operation in the short-pulse regime because of the existence of an operational regime, the breakdown-insensitive acceleration regime (BIAR), where disturbances in secondary pulses are observed but the main acceleration pulse is still intact. In this talk, the experimental results and dark current simulations of the metamaterial accelerator will be presented.
In wakefield LPA the use of special plasma profiles has a significant effect. Earlier (see [1-2]) it was shown that with a longitudinal growing plasma density due to the compression of the wake bubble, synchronicity of the maximum acceleration field in the region of the rear wall of the bubble and the bunch is achieved. However, in the blowout regime, the radial force is uniform along most of the bubble $F_r$, and $F_r$ is proportional $r$. Then the radial oscillations of the bunch electrons are harmonic and the transverse instability of the bunch occurs. Studies [3] show that instability is significantly suppressed due to anharmonic oscillations of bunch, if the $F_r$ is inhomogeneous. The problem of instability can be solved in a weakly nonlinear regime, when not all plasma electrons leave the bubble. Then $F_r$ is inhomogeneous. The inhomogeneity of the distribution of residual plasma electrons leads to anharmonic oscillations of the bunch and stabilization of the bunch. In this report, by numerical simulation using the OSIRIS code [4], it was demonstrated that it is possible to ensure the simultaneous presence of the bunch in the acceleration phase and in the region where it is acted upon by an inhomogeneous $F_r$.
1. V.I.Maslov et al. Photonics. 9 (2022) 174.
2. A.Picksley et al. 6th Eur. Adv. Accel. Conc. Workshop. 2023, Isola d’Elba.
3. Martinez de la Ossa A et al. Phys. Rev. Let. 121 (2018) 064803.
4. Fonseca R.A. et al. Computational Science - ICCS. 2002. LNCS 2331. P. 342
Next generation laser drivers for laser plasma acceleration and secondary radiation sources will require 3 to 4 orders of magnitude increase in pulse repetition rates, to produce TW-PW class peak power ultrashort pulses at multi-kilowatt average powers [1]. Coherently combined ultrashort pulse fiber laser systems are recognized as a pathway to such high power technology [1]. However, although the current state-of-the-art high-power coherently combined fiber laser systems have demonstrated a relatively large number of combined channels ranging from 16 and up to 61 so far, but they all achieved only moderate femtosecond pulse energies in the 10-30mJ range, far below what is needed for driving particle-acceleration experiments.
We had developed a novel time-domain coherent combining technique (coherent pulse stacking amplification - CPSA) that enables 100 times higher energies per channel than conventional fiber CPA, achieving record high femtosecond pulse energies of up to ~10mJ per channel, far exceeding any other fiber laser results. This opens an effective pathway to reaching higher pulse energies, which we recently validated in a 4-channel coherently-spatially combined array, producing ~27mJ per spatially and temporally combined beam [2]. We will report the development of a 12-channel table-top laboratory system upgrade to produce 100mJ/1kW spatially and temporally combined beams, which after compression are sufficient for acceleration and secondary-radiation experiments. This work includes development of a new energy-scalable pre-pulse cleaning technique necessary for driving majority of high-intensity laser plasma interactions. This development constitutes an important milestone towards future multi-kW average and TW-kW peak power laser drivers.
A major challenge for any experiment involving laser - electron beam interaction such as Compton scattering, dielectric laser accceleration or ponderomotve bunching is spatiotemporal overlap of the pulses. In this paper, we demonstrate how a simple electro-optic sampling setup can be used as a tool to read out the spatiotemporal overlap of an electron bunch and laser pulse. By using an intercepting geometry where the electron beam is sent directly into the electro optic ZnTe crystal, the induced fluorescence signal is imaged onto a CCD camera allowing for beam spotsize measurements concurrently with the time-information extracted by EOS analysis. This is then used to reconstruct the full longitudinal and transverse shape of the electron bunches allowing beam analysis for future experiments that require laser – electron beam interactions. At the UCLA Pegasus beamline, the setup is used to study velocity compression of a low charge 4-6 Mev beam using an RF cavity. We show a clear EOS signal even at beam charges below 1 pC, owing to the strong electric field of the fully compressed e-beam.
EuPRAXIA@SPARC_LAB will be a user-oriented X-ray free-electron laser, based on plasma wakefield acceleration. A 20 pC, 500 MeV witness electron bunch will be injected in plasma with density ~10^16cm-3,accelerated to >1 GeV and delivered to undulators for generating radiation in the water-window region (~4nm).
To preserve beam quality upon acceleration in plasma, the envelope of the witness bunch must be matched to the focusing force present in the ion column generated by the 500 pC drive bunch. In this contribution, we discuss the requirements for the measurement of transverse size and position of the witness bunch the plasma entrance, as well as the other compact diagnostics needed along the RF linac and the transfer line to the undulators.
The impediment of collective beam effects, including coherent synchrotron radiation (CSR) is a critical challenge in the generation of high-brightness beams, requiring new theoretical and experimental insight. This work will outline plans for a sequence of upcoming experiments at the Argonne Wakefield Accelerator (AWA) that leverages both the large parameter space for the bunch charge and size, various bunch profiles (round and flat beams) as well as the capability of generating shaped bunches through laser shaping and the emittance exchange. In particular, we will discuss an upcoming CSR shielding study using a dipole chamber with a variable gap size along with plans for future experiments that benchmark the effect of CSR on the beam phase space in a laser-shaped short electron bunch. This work is part of a comprehensive analysis including the development of novel self-consistent CSR simulation methods and theoretical analysis. The results of the experimental components, in addition to providing benchmarks for the theoretical developments, will explore the parameter bounds of 1/2/3D CSR effects on beam dynamics, evaluate CSR effects on complex beams and eventually be used to propose mitigation strategies.
This research was supported by the U.S. Department of Energy, Office of Science, Office of High Energy Physics under Award DE-SC0024445.
Traditional particle-in-cell (PIC) computational plasma simulations are subject to finite grid instabilities (FGI). This instability is attributed to excited high frequency modes being aliased to lower modes resolvable by the grid. The relationship between FGI and aliasing can be examined by comparing the outputs from gridded simulations (both momentum-conserving and energy-conserving) to those from simulations solved using a Fourier basis. By projecting the fields onto a truncated Fourier basis rather than a spatial grid, aliasing can be avoided. Concurrently with the simulation outputs, mathematical bridges to move from gridded algorithms to Fourier representations, and vice versa, are being investigated. Single-mode analysis to compare growth rates with simulation outputs can also demonstrate the extent of the connection between aliasing and FGI.
Plasma wakefield accelerators (PWFA) have showcased remarkable acceleration gradients, reaching tens of GeV per meter. Advancements in generating high-quality beams via self-injection schemes and pursuing attosecond electron beams represent the forefront of this field. In this work, we introduce a novel approach to inject a high-quality electron beam using beam-induced ionization injection (B-III) with a driver-injector beam configuration. In B-III, the field of a particle beam intensifies as its slice envelope oscillates towards its minimum value due to the betatron oscillation, whereby it further ionizes electrons of an impurity element for subsequent injection. We will explain the physical underpinnings of this design using analytics plasma wakefield theory and present supporting Particle-In-Cell (PIC) simulation results that show the potential for creating an injected beam with ~500 attosecond duration, hundreds of nanometer emittance, and less than 1% energy spread. Furthermore, we will present the prospect of realizing this beam experimentally at FACET II, where the desired driver-injector beam configuration would be attained by control over compression and selection of the beam phase space using a collimator. This technique is routinely performed for generating two beams in drive-trailing PWFA experiments at FACET II. Results from Lucretia, a physics toolbox simulating electron beam through FACET-II transportation line, will be presented to demonstrate the feasibility of generating the required drive-injector beam. Finally, we will present the potential application of the injected beam in generating attosecond Free Electron Laser (FEL).
Acceleration by the wakefield provides compact sources of electron bunches of high brightness [1]. Electron–positron colliders and x-ray microscopes require bunches with low energy spread. In the blowout regime, the radial force is uniform along the wakefield bubble $F_r=const$ and $F_r(r)$ is proportional to $r$. These lead to the harmonicity of the radial oscillations of the bunch. Harmonicity leads to the bunch instability [2]. Other authors [3] demonstrate that the instability is suppressed by anharmonic oscillations if $F_r(z)$ is inhomogeneous along the bubble. We present the instability suppression in the weakly nonlinear regime, in which not all plasma electrons leave the bubble. Then $F_r$ is inhomogeneous for driver- and witness-bunches. The radial inhomogeneity of the distribution of residual plasma electrons leads to the bunch stabilization. At the distance from the head of the driver, where plasma electrons have not left the axis, the driver can be continuous and stationary. At distance from the back front of the bubble, where there are plasma electrons, the witness can be continuous, remaining stationary. At that distance from the head of driver-bunch, where plasma electrons have left the axis, but not all plasma electrons have left the bubble, the driver-bunch can be stationary, if it is hollow cone. The side of the cone should go along the bubble boundary.
1. W.P.Leemans et al. Phys. Rev. Lett. 113, 245002 (2014).
2. M.Litos et al. Nature. 515, 92 (2014).
3. A.Martinez de la Ossa et al. Phys. Rev. Let. 121, 064803 (2018).
Plasma accelerators exhibit O(10) GeV-level electric fields, promising a compact linear accelerator design. Reaching the collider-relevant TeV-level beam energy necessitates the use of multiple consecutive stages to replenish the wake-driving beam. The stage-to-stage coupling is thus an elementary design aspect of plasma accelerator development, which demands for excellent charge coupling and focus control while being compact. In this contribution, we discuss various designs
for inter-stage couplings from first principle, with a focus on the associated length and chromaticity acceptance.
This work was supported by the Director, Office of Science, Office of High Energy Physics, of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231.
Traditional linear accelerators (LINACS) are effective for accelerating large amounts of ion charge with high efficiency. However, their compactness is limited by the breakdown of the solid accelerating structure, typically on the order of MV/m. On the other hand, laser-target ion accelerators can produce much higher accelerating field, e.g. via a TNSA mechanism, but are limited in the resulting ion energy gain by the small size of their acceleration region. In this talk I will revisit and extend the concept of Ionization Front Acceleration (IFA), first introduced in the 1980s. The IFA approach combines the compactness of laser plasma ion accelerators with the high efficiency, brilliance, and extended acceleration distances characteristic of traditional LINACS. In this scheme, an intense relativistic electric beam is directed into a gas medium, while a sweeping external laser ionizes the gas, propelling the ionization front forward. This creates an acceleration region with gradients of sub-gigavolt per meter(~300MV/m) that co-propagates with the injected ions, offering the potential for a compact, high-yield ion accelerator. Using particle-in-cell simulations, we demonstrate the acceleration of 150 MeV few-μC hydrogen ions over a distance of < 0.5m. Additionally, we propose an innovative scheme, termed Counter-propagating Laser-Ionization Front (CLIF) acceleration, to overcome the hosing instability of the driver beam that limits the final energy -- a potential challenge that was not explored in the earlier IFA research.
The time for stationary plasma to recover its original state after a wake is excited determines repetition rate and luminosity of plasma-based colliders. Recent measurements at DESY [1] showed that an argon plasma of density ne ≈ $10^{16}$ cm$^{-3}$ in which a 0.5 J (0.5 nC, 1 GeV) e-bunch excited a first wake supported excitation of a second wake at the same location with indistinguishable beam properties within 60 ns. Here, we report Spring 2024 results of experiment E-324 at SLAC's FACET-II in which 20 J (2 nC, 10 GeV) e-bunches excited meter-long nonlinear wakes in stationary lithium, hydrogen, and argon plasmas of density ne ≈ $10^{16}$ cm$^{-3}$. Scattered light from a 1 mJ, 100 fs optical pulse impinging on the plasma filament at grazing incidence (~1˚) at delays 1 ns ≤ ∆t ≲ 1 ms then sensitively probed wakefield remnants. In lithium plasma, probe scatter peaked at ∆t ≈ 100 ns and remained visible out to ∆t ≈ 2 microseconds. In contrast, no scattering was visible from the e-beam-excited hydrogen plasma beyond ∆t ≈ 100 ns; scattering from Argon disappeared at ∆t ≈ 300 ns. The results will be discussed in light of earlier findings of experiment E-224 [2], which showed that ion motion dominated energy transport out of the beam-excited region for ∆t ≳ 0.3 ns.
References:
[1] R. D’Arcy et al., Nature 603, 58-62 (2022).
[2] R. Zgadzaj et al., Nat Commun 11, 4753 (2020).
Precise control of the temporal shape of ultrashort pulses of terawatt scale peak power is often desirable in experiments. In previous work, we used single, few-cycle 5 fs pulses for 1 kHz rep. rate laser wakefield acceleration (LWFA) to 15 MeV in near-critical density hydrogen plasma [1]. Double pulses are also of interest for LWFA, as prior simulation studies suggest that resonant driving of wakes enhances injection and acceleration [2]. However, prior methods for generating double few-cycle pulses exhibit energy loss of up to 80% [3]. Our method [4] utilizes precise control of oscillator seed pulses before chirped pulse amplification.. Pulse peak separations as short as 10 fs (~4 cycles) are generated [4]. We present the double pulse generation scheme, particle-in-cell simulations suggesting that the interaction of these pulses in plasma can tunably modify and enhance electron acceleration and injection, and preliminary experimental results.
[1] F. Salehi et al., Phys. Rev. X 11, 021055 (2021).
[2] C. Kim et al., Phys. Lett. A 370, 310 (2007)
[3] A. Catanese et al., OSA Contin. 4, 3176 (2021).
[4] L. M. Railing et al., Opt. Lett. 49, 1433-1436 (2024)
The first demonstrations of fully optical multi-GeV laser wakefield acceleration (LWFA) have been enabled by the advent of low density (~1017 𝑐𝑚−3), meter-scale plasma waveguides generated in supersonic gas jets [1-8]. In this talk, I will present results from our recent LWFA experiments using plasma waveguides up to 30 cm in length, which have produced sub-milliradian divergence electron bunches with nC-level charge in the 1-10 GeV range [7,8]. I will also discuss our extensive simulation efforts, which are motivated by physics understanding and optimization of accelerator performance. These efforts include models of meter-scale hydrodynamic waveguide formation and their experimental benchmarking [9], and new, important regimes of LWFA drive pulse propagation [6] that strongly affect the laser wakefield acceleration dynamics. Finally, I will discuss the use of consistent, high charge multi-GeV electron bunches to generate muons in high-Z materials.
Funding Acknowledgements: This work was supported by the U.S. DoE (DE-SC0015516, LaserNetUS DE-SC0019076/FWP#SCW1668, and DE-SC0011375), NSF (PHY2010511), DARPA’s Muons for Science and Security Program (MuS2). Simulations used DoD HPC support provided through ONR (N00014-20-1-2233). E.R. is supported by NSF GRFP (DGE 1840340). Portions of work prepared by LLNL under Contract DE-AC52-07NA27344.
[1] Feder et al., PRR 2, 043173(2020).
[2] Picksley, A., et al. PRE 102.5, 053201(2020)
[3] Shrock et al., Phys. Plasmas 29, 073101(2022).
[4] Miao et al., PRX 12, 031038(2022).
[5] Miao et al., Physics Today 76 (8), 54-55(2023).
[6] Shrock et al., PRL(2024).
[7] Shrock et al., In preparation(2024).
[8] Rockafellow et al., In preparation(2024).
[9] Miao et al., PRAB(2024)
We attempt to combat the quadrupole-mode transverse wakefields inherent in planar-symmetric dielectric structures by periodically rotating the structure 90 degrees about the beam axis so that the beam sees an alternating quadrupole-like field as it progresses through the entire structure. We study this configuration experimentally in a two-period structure where the gap in each transverse dimension can be controlled independently. This allowed us to independently control the wakefields associated with each orientation of the structure. We demonstrate the existence of strong transverse wakefields with an asymmetric gap and the mitigation of the effects of those wakefields with a symmetric structure. We study the effect of the structure on beam emittance as well as a slice-wise analysis of the transverse wakefield effects. We employ particle in cell simulations to better understand the details of the beam-structure interaction.
Coherent synchrotron radiation (CSR) is a limiting effect in linear accelerators with dispersive elements due to its contribution to projected transverse emittance growth. This effect becomes a limitation for highly compressed beams. Even though CSR-induced projected emittance growth has been widely studied, conventional measurement techniques are not detailed enough to resolve the multi-dimensional structure of the beam, namely the different rotations of transverse phase space slices throughout the longitudinal coordinate. In this work, we simulate the reconstruction of a CSR-affected beam after a double dogleg at the Argonne Wakefield Accelerator Facility by using our generative-model-based six-dimensional phase space reconstruction method. Additionally, we study the current limitations of the phase space reconstruction method and perform an analysis of its accuracy and precision in simulated cases in preparation for the experimental demonstration.
Radio frequency (RF) electromagnetic radiation in the form of an electromagnetic pulse (EMP) resulting from high intensity laser plasma experiments can damage essential scientific diagnostics in experiments relevant to advanced accelerator concepts, particularly in the petawatt era of lasers. Here we compare the EMP in three different experiments: a direct laser acceleration (DLA) experiment and two laser-wakefield acceleration (LWFA) experiment. The DLA experiment was at the Texas Petawatt, where a laser pulse of 150 fs, 100 J, focused by an f/40 parabola onto a supersonic hydrogen gas jet target with density from 10^18 cm^-3 to 10^19 cm^-3. The first LWFA experiment was in HERCULES, where laser pulse of 39 fs, 9 J, focused by an f/40 parabola onto a gas cell of nitrogen-doped helium with electron density of 4 x 10^18 cm^-3. The second LWFA experiment was in the ZEUS laser facility, where a laser pulse of similar parameters to the HERCULES experiment focused instead onto a gas jet of nitrogen-doped helium. PIC simulations with experiment-relevant parameters will also be discussed.
A train of charged particle bunches can resonantly drive large amplitude wakefields in plasma, when spaced by integers of one plasma wavelength, and high-transformer-ratio wakefields, when spaced by integers of half plasma wavelength and with properly ramped bunch density. We show with numerical simulations that the SPARC_LAB linear accelerator can provide a train of compressed electron bunches via the velocity bunching technique, and that the coupling between the bunch train and plasma can allow for large-amplitude wakefield excitation (resonant configuration) and for high-transformer-ratio acceleration (anti-resonant configuration). We discuss the experimental plan at SPARC_LAB.
Ultrashort transverse Faraday-rotation probes of laser-driven wakefield accelerators (LWFAs) have measured kilo-T magnetic fields originating from accelerating electrons and bubble sheath currents in plasmas ranging in density from >10^19 [1] to 10^17 cm-3 [2]. Such measurements have revealed e.g. wake size and shape [1,2], bunch duration [3], and longitudinal charge distribution within a bubble [2] at one location within the plasma. Here we describe a comprehensive obliquely-incident probe of all components a wake's magneto-optic tensor, including Faraday and Cotton-Mouton effects, using a three-channel Stokes polarimeter [4]. In addition, we have multiplexed the probe and detection system to record magneto-optic images at several locations along the wake's propagation path in one shot. Anticipated physics studies include dependence of B-field evolution on electron injection method, evolution of bubble size and intra-bubble charge distribution during multi-GeV beam-loaded LWFA [5],and B-field evolution during electron-beam-driven plasma wakefield acceleration.
[1] M. C. Kaluza et al.,"Measurement of magnetic-field structures in a laser-wakefield accelerator," Phys. Rev. Lett. 105, 115002 (2010).
[2] Y. Y. Chang et al.,"Faraday rotation study of plasma bubbles in GeV wakefield accelerators," Phys. Plasmas 28, 123105 (2021).
[3] A. Buck et al.,"Real-time observation of laser-driven electron acceleration," Nat. Phys. 7, 543 (2011).
[4] P. F. Colleoni et al.,“Space and time resolved measurement of surface magnetic field in high intensity short pulse laser matter interactions,” Phys. Plasmas 26, 072701 (2019).
[5] C. Aniculaesei et al.,"The acceleration of a high-charge electron bunch to 10 GeV in a nanoparticle-assisted wakefield accelerator," Matter Rad. Extremes 9, 014001 (2024).
Betatron radiation produced from a laser-wakefield accelerator (LWFA) is a broadband, hard X-ray (> 1 keV) source that has been used in a variety of applications in medicine, engineering and fundamental science. Recent advances in laser technology has enabled increases in shot-rate and system stability providing improved statistical analysis and detailed parameter scans. However, unique challenges exist at high repetition rate (> 1 Hz), where data throughput and source optimization is now limited by diagnostic acquisition rates and analysis. The characterization of betatron radiation is typically performed by measurements of the X-ray transmission through a series of filters that consist of multiple materials and thicknesses with unique transmission curves. We present the development of a machine-learning-assisted X-ray spectrometer designed to reconstruct spectral characteristics of betatron sources produced by LWFA. A neural network model was used to extract the critical energy and source amplitude from the data in real-time with an average reconstruction time of ~ 4 ms, which provides a 20x increase in speed compared to traditional analysis that uses a forward fitting algorithm to reconstruct only the critical energy. We report on the fielding of this deep learning algorithm for on-line source characterization at the INRS-EMT’s Advanced Laser Light Source (ALLS), and discuss future plans to implement the algorithm towards real-time optimization of betatron radiation at ALLS.
Ultra-intense lasers in the long-wavelength infrared (LWIR) spectral region are particularly attractive to the areas of ultrafast and strong-field science, primarily due to favorable quadratic scaling of the ponderomotive potential with the laser wavelength, which benefits accelerator research. However, advancing LWIR lasers peak power faces significant challenges due to intensity-dependent effects, such as nonlinear refractive index changes, absorption in transparent optics, and laser-induced damage to optical components. These issues can potentially degrade laser performance.
While these properties are frequently studied using short-pulse lasers in the ultra-violet to mid-infrared wavelength range, their manifestation at longer wavelengths has not been extensively investigated. Consequently, there is a lack of reliable data on materials’ nonlinear properties and laser damage thresholds under ultra-short LWIR pulses near a 9 µm wavelength.
In our research, we present the nonlinear optical properties and preliminary damage threshold measurements for selected transparent LWIR laser optics and mirrors. Experiments were conducted using a high-peak power 9.2 µm laser, switchable between 2 ps and 70 ps pulse durations. For damage threshold measurements, samples were characterized ex-situ using optical microscopy to estimate the damage areas, which scale linearly with the logarithm of pulse energy for near-Gaussian beams.
Long-wave infrared (LWIR) lasers are well-suited for applications such as laser wakefield acceleration and high harmonic generation due to the favorable wavelength scaling of the ponderomotive force. Using CO2 amplifiers, multi-terawatt peak powers with sub-picosecond pulse durations have been demonstrated. However, a limiting factor for these amplifiers is the current necessity of using electrical discharges to pump the gain medium, reducing the maximum repetition rate and energy stability. Scaling a terawatt CO2 laser to repetition rates of 100-1000 Hz will likely necessitate switching from electrical discharge pumping to optical pumping. The optimal excitation for pumping is centered at 4.3 $\mathrm{\mu}$m; however, slight detuning is necessary to manage absorption in the gain medium. We demonstrate a proof of principle of the generation of a 4.5 $\mathrm{\mu}$m pump, by utilizing stimulated Raman scattering, a process where photons inelastically scatter from a material. Since typical Raman materials do not have the correct vibrational spectrum to generate this wavelength, we employ a novel class of material known as ionic liquids as the Raman medium. We demonstrate efficient conversion from a 532 nm frequency doubled Nd:YAG laser to 603 nm in the ionic liquid EMIM DCA, followed by performing difference frequency generation to produce the 4.5 $\mathrm{\mu}$m pump.
Compression of amplified laser pulses beyond the limits of a compressor grating-setup has been a fruitful topic of research for decades. Filamentation compression offers a solution which benefits from a higher energy capacity and being easier to couple light into than the the hollow-core fiber compression scheme. Here, 40 fs CPA laser pulses with 40 nm FWHM bandwidth are spectrally-broadened and compressed. Additionally, a genetic algorithm is implemented in the execution of these experiments using a deformable mirror and a Dazzler acoustic-optic programmable dispersive filter with myriad feedback parameters and figures of merit. This allows optimization of the parameters of the experiment including energy throughput and output pulse duration. An experimental analysis of the post-filamented beam’s spatial profile, spectrum, and pulse length is presented along with optimization characterizations utilizing the genetic algorithm.
“Flying focus” techniques produce laser pulses with dynamic focal points that can travel distances much greater than a Rayleigh length. The implementation of these techniques in laser-based applications requires the design of optical configurations that can both extend the focal range and structure the radial group delay. This work describes a method for designing optical configurations that produce ultrashort flying focus pulses with arbitrary-trajectory focal points [1]. The method is illustrated by several examples that employ an axiparabola for extending the focal range and either a reflective echelon or a deformable mirror-spatial light modulator pair for structuring the radial group delay. The latter configuration enables rapid and automated exploration and optimization of flying foci, which could be ideal for experiments. This material is based upon work supported by the Department of Energy Office of Fusion Energy under Award Number DE-SC0021057 and by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0004144.
[1] M. V. Ambat, J. L. Shaw, J. J. Pigeon, K. G. Miller, T. T. Simpson, D. H. Froula, & J. P. Palastro, “Programmable-trajectory ultrafast flying focus pulses,” Opt. Exp., 31, 19 (2023).
Two-beam acceleration is a powerful method to generate high accelerating fields by utilizing short radiofrequency pulses. The Argonne Wakefield Accelerator facility is applying a two-beam acceleration approach to an X-band radiofrequency gun. This gun has experimentally demonstrated an electric field on the photocathode of ~400 MV/m. The next phase of this experiment will involve adding a short X-band linac to boost the beam energy up to ~10 MeV. This paper summarizes the optimization of the linac and beam dynamics simulations in the integrated system over a wide range of operating parameters and demonstrates that the available setup will support the generation of bright or ultrashort beams with possible applications to compact light sources including inverse Compton scattering.
Longitudinally shaped electron bunches are useful in wakefield acceleration, allowing for transformer ratios greater than 2. Electro-optic sampling can provide an accurate and non-destructive determination of the electron bunch current profile by measuring the transverse terahertz electric field of the electron bunch. Specifically, electro-optic sampling using the phase diversity reconstruction algorithm has been shown to provide an accurate picture of ultra-short bunch profiles, as well as long bunches and bunch trains requiring long data acquisition windows. In addition bunch profile monitoring, this setup can also be used to measure bunch arrival-time and bunch charge. In this paper, we discuss our work on designing and engineering an electro-optic sampling setup employing phase diversity at the Argonne Wakefield Accelerator (AWA). This includes a tabletop measurement of a THz pulse created via optical rectification using a regenerative
amplified Titanium Sapphire laser pulse, a beamline measurement of the electron beam current profile using transition radiation, and a design for a beamline measurement of the electron bunch Coulomb field. We also include finished simulations of shaped electron beam reconstructions using the phase diversity algorithm using different crystal species, crystal thicknesses, and laser bandwidths from first principles.
Laser Wakefield Acceleration (LWFA) offers a promising alternative to conventional accelerators, offering superior acceleration gradients. However, the effect of radiation reaction inside the wake-field can be detrimental to their operation. The transverse focusing field in the wakefield can drive betatron oscillations and cause radiation emission, with radiation back-reaction effects on the elec-tron dynamics becoming stronger as the beam energy gradually increases during acceleration. As the beam energy exceeds 100 GeV, the radiation reaction behavior will deviate from the classical beavior and quantum radiation effects will cause a "stochastic heating," which can be an intrinsic beam energy spread mechanism for high-energy accelerators. The radiation can also dampen the transverse energy spread of the beam, causing radiative emittance reduction. Due to the dephasing and laser depletion, the operation of TeV class beam collider based on LWFA technology will re-quire multiple LWFA stages, or using structured light as a driver. The coupling efficiency between two acceleration stages depends highly on the beam emittance and energy spread. Thus, understand-ing how radiation reaction effects influence the evolution of beam energy spread and emittance is an essential factor for constructing an LWFA-based TeV class beam collider. We also investigate the evolution of spin polarization in LWFA’s by employing our spin and polarized resolved QED mod-ule based on a particle-in-cell (PIC) code OSIRIS to predict the effect of radiation emission on the transport and acceleration of polarized beams.
This work is supported by the US National Science Foundation Award # 2108075.
Quasi-static (QS), particle-in-cell (PIC) algorithms are extremely efficient methods for modeling plasma-based acceleration (PBA) driven by an intense laser or particle beam. Compared to conventional PIC methods, QS-PIC codes can speed up simulations by several orders of magnitude due to the larger time-steps permitted. These computational savings permit high-fidelity modeling of intractable physical problems such as hosing and ion motion in PBA. Recently, we proposed and implemented a new hybrid PIC algorithm, QPAD [1], that combines the QS algorithm with a quasi-3D Fourier azimuthal decomposition [2]. QPAD decomposes the electromagnetic fields, charge and current density into azimuthal Fourier harmonics on a cylindrical grid, which reduces the algorithmic complexity of a 3D code to that of a 2D code. It can therefore provide several orders of magnitude speedup over standard 3D QS codes and is uniquely suited for high fidelity simulations over long distances, parameter scans, and optimization problems. QPAD features an azimuthally decomposed ponderomotive guiding center (PGC) algorithm for modeling laser-plasma interactions, a robust predictor-corrector pusher for modeling highly nonlinear wakes, and implementations of Arbitrarily structure laser (ASTRL) pulses. Examples of QPAD simulations of beam-driven and laser driven wakefields, plasma matching sections, realignment of the witness beam, and fully self-consistent efficient beam loading stages for the electron arm of a LC are presented. Comparisons with fully 3D explicit PIC codes are also presented.
This work is supported by DOE and NSF.
[1] F. Li et al., CPC, 261, 107784 (2021).
[2] A. F. Lifschitz et al., JCP, 228, 1803–1814 (2009).
Laser driven ion acceleration provides a route to achieve high quality ion beams, which could be superior for specific applications. In this talk I will present recent development of a laser driven ion acceleration beam line at Shanghai Institute of Optics and Fine Mechanics (SIOM). Meanwhile I will also give an update on the current status of the 10 PW and 100 PW Laser systems at SIOM.
Fully relativistic particle-in-cell (PIC) simulations continue to be a critical pillar in plasma-based advanced accelerator concepts research. Modern state-of-the-art GPU supercomputers offer the potential to perform PIC simulations of unprecedented scale, but require robust and feature-rich codes which can fully leverage the computational resources. We have addressed this demand by adding GPU acceleration to the PIC code OSIRIS. We present an overview of CUDA implementation, some performance results, and simulations illustrating the capabilities of the code, including (1) thermal plasma simulations demonstrating strong absolute performance and weak scaling and (2) simulations of laser wakefield acceleration with dynamic load balancing. Areas for future effort will also be discussed.
Work supported by DOE and NSF.
Laser wakefield accelerators (LWFAs) are capable of supporting accelerating and focusing forces on the order of 10 - 100 GeV/m, about three orders of magnitude greater than conventional RF accelerators. While theoretical solutions for the electromagnetic (EM) focusing fields have been developed, the field structures have yet to be verified experimentally. In this poster, we present simulation results for transverse probing of laser wakefields using ultrarelativistic electrons. We study the behavior of the probing electrons by implementing filtering masks to investigate focusing characteristics of thin electron “bands”. The deflection of these bands after propagating through the wakefield is then used to characterize the EM forces. The simulated focusing behavior of these electron bands is in reasonable agreement with a theoretical model developed based on a “thin lens” model of the wakefield. Simulation results show the focusing of the bands to be an effective experimental diagnostic for verifying the EM field structure. This provides an analytic framework needed for the first direct measurements of focusing forces in an LWFA at the Accelerator Test Facility at Brookhaven National Lab.
We have performed periodic, one-dimensional particle-in-cell (PIC) simulations to test the numerical stability of a variety of explicit energy-conserving PIC algorithms. When an optical-field-ionized (OFI) plasma column expands, it can create a radially propagating shock in the surrounding gas. Ionization of this shocked gas has enabled recent experiments to achieve low density (~$10^{17} \text{ cm}^{-3}$) plasma channels with matched spot sizes on the order of $10 \text{ $\mu$m}$ and attenuation lengths in excess of one meter [Picksley (2020), Shrock (2022)]. However, these experiments are operating on the edge of the validity of fluid approximations: the elastic cross section for hydrogen is approximately $10^{-19} \text{ m}^2$ which yields a mean free path of $10 \text{ $\mu$m}$ at a gas density of $10^{18} \text{ cm}^{-3}$. Thus, creation of lower density plasma waveguides will require a careful study of the kinetic interactions between the expanding ions and the surrounding gas using PIC simulations.
Unfortunately, PIC suffers numerical instabilities when the Debye length is not resolved, and when the drift velocity of the plasma exceeds the thermal velocity. We present numerical measurements of the stability and noise for each of the considered methods, as well as analytic results for some stability conditions. We find that energy-conserving PIC algorithms are ideally suited for simulating plasma channel expansion, and that numerical instabilities do not arise in this region of parameter space.
Work supported by:
AFOSR FA9550-18-1-0436
NSF (PHY) 2206647
Laser-plasma accelerators (LPAs) have potential to enable compact light sources and high-energy linear colliders. At the BErkeley Lab Laser Accelerator (BELLA) PW facility, electron bunches with energy up to 8 GeV have been generated using laser pulses with peak power of 0.85 PW (energy 31 J) and an acceleration length of 20 cm. In order to accelerate over this distance of 15 diffraction lengths, a preformed plasma waveguide based on inverse bremsstrahlung (IB) heating inside a capillary discharge was used [1]. Simulations showed that the energy gain can be increased to beyond 10 GeV, but with lower density than is achievable with IB heating. The recent addition of a second beamline to BELLA PW has allowed for the use of plasma channels formed by optical field ionization (OFI) [2-4], which enables optimized density profiles. We will present guiding and acceleration results using this new capability with beams ~10 GeV. Additionally, we will present muon generation results from beams accelerated using OFI plasma channels.
The ongoing Plasma-driven Attosecond X-ray source experiment (PAX) at FACET-II aims to produce coherent soft X-ray pulses of attosecond duration using a Plasma Wakefield Accelerator [1]. These kinds of X-ray pulses can be used to study chemical processes where attosecond-scale electron motion is important. For this first stage of the experiment, PAX plans to demonstrate that <100 nm bunch length electron beams can be generated using the 10 GeV beam accelerated in the FACET-II linac and using the plasma cell to give it a percent-per-micron chirp. The strongly chirped beam is then compressed in a weak chicane to sub-100nm length, producing CSR in the final chicane magnet at wavelengths as low as 10s of nm. In this contribution we describe the developments in commissioning the experiment as well as the expected results.
Additionally, we describe a future iteration of the experiment in which short undulators are used to drive coherent harmonic generation to produce attosecond gigawatt X-ray pulses at 2 and 0.4 nm, with lengths comparable to the shortest attosecond pulses ever measured at 2 nm using HHG.
[1] C. Emma, X.Xu et al APL Photonics 6, 076107 (2021)
The Zettawatt Equivalent Ultrashort pulse laser System (ZEUS) is a National Science Foundation-funded user facility located at the University of Michigan in the US. The laser will be capable of producing 3-Petawatt pulses and can also be split to create synchronized 2.5-PW and 0.5-PW pulses. This presentation will describe the different capabilities of the facility available to users in each of the three target areas and the current laser status and recent results from first experiments on laser wakefield acceleration and x-ray generation.
FLASHForward is a beam-driven plasma-wakefield accelerator (PWFA) experiment at DESY, acting as a test bench to develop technologies to accelerate electron beams with high quality and high average power. By enhancing conventional acceleration methods with plasma acceleration, the cost and footprint of future accelerators could be significantly reduced. To achieve this, it is crucial to have detailed knowledge of plasma dynamics, both spatially and temporally, in the plasma accelerator stage. FLASHForward utilises discharge capillary plasma sources. An in-house hydrodynamic plasma model was used to simulate these sources. Simulated plasma density profiles are then input into particle-in-cell (PIC) codes to simulate beam-plasma interaction. In this contribution, such simulations are compared to experimental measurements of electron bunch deceleration to provide insight into transverse plasma density redistribution at microsecond timescales.
Recent advances in multi-GeV laser wakefield acceleration (LWFA) depend on plasma waveguides initiated by intense Bessel beam pulses [1,2]. We demonstrate for the first time the generation and characterization of Bessel-like beams using highly customizable eight-level diffractive logarithmic axicons. The high degree of tunability achievable with these optics enables controllable axial laser intensity profiles and can potentially produce longitudinally uniform meter-scale plasma waveguides for LWFA.
We present measurements characterizing the extended focal lines produced using various diffractive logarithmic axicons fabricated at the University of Maryland. This includes generation of a funnel-shaped intensity distribution at the onset of the focal line and a demonstration of diffraction efficiency improvement with the number of levels.
This work was supported by the U.S. Department of Energy (DE-SC0015516), and the National Science Foundation (PHY1619582 and PHY2010511).
References:
[1] Miao, B., Shrock, J. E., Feder, L. et al., Multi-GeV Electron Bunches from an All-Optical Laser Wakefield Accelerator, Phys. Rev. X 12, 031038, (2022).
[2] B. Miao, E. Rockafellow, J. E. Shrock, S. W. Hancock, D. Gordon, and H. M. Milchberg, Benchmarking of hydrodynamic plasma waveguides for multi-GeV laser-driven electron acceleration, arXiv preprint arXiv:2404.13632 (2024).
The recent development of advanced black box optimization algorithms has promised order of magnitude improvements in optimization speed when solving accelerator physics problems. These algorithms have been implemented in the python package Xopt, which has been used to solve online and offline accelerator optimization problems at a wide number of facilities, including at SLAC, Argonne, BNL, DESY, ESRF, and others. In this work, we describe updates to the Xopt framework that expand its capabilities and improves optimization performance in solving online optimization problems. This includes significant improvements in Bayesian optimization algorithms, such as trust region Bayesian optimization and Bayesian algorithm execution for optimizing virtual objectives. We also discuss how Xopt has been incorporated into the Badger graphical user interface that allows easy access to these advanced control algorithms in the accelerator control room.
Accelerator-based x-ray free-electron lasers (XFELs) are the latest addition to the revolutionary tools of discovery for the 21st century. The two major components of an XFEL are an accelerator-produced electron beam and a magnetic undulator, which tend to be kilometer-scale long and expensive. A proof-of-principle demonstration of free-electron lasing at 27 nm using beams from compact laser wakefield accelerators was shown recently by using a magnetic undulator. However, scaling these concepts to x-ray wavelengths is far from straightforward as the requirements on the beam quality and jitters become much more stringent. Here, we present an ultracompact scheme to produce tens of attosecond x-ray pulses with several GW peak power utilizing a novel aspect of the FEL instability using a highly chirped, prebunched, and ultrabright tens of MeV electron beam from a plasma-based accelerator interacting with an optical undulator. The FEL resonant relation between the prebunched period and the energy selects resonant electrons automatically from the highly chirped beam which leads to a stable generation of attosecond x-ray pulses. Furthermore, two-color attosecond pulses with subfemtosecond separation can be produced by adjusting the energy distribution of the electron beam so that multiple FEL resonances occur at different locations within the beam. Such a tunable coherent attosecond x-ray sources may open up a new area of attosecond science enabled by x-ray attosecond pump/probe techniques.
Structure wakefield accelerators (SWFAs) offer a path to high accelerating gradient using either collinear wakefield acceleration or two-beam acceleration (TBA). In the past five years, significant progress has been made in operating accelerating structures powered externally by short radiofrequency pulses generated from thew wakefield of decelerating bunches. Such a TBA approach has demonstrated the operation of X-band accelerating structures with surface electric fields approaching GV/m, including a radio-frequency photoinjector with photocathode field close to 0.4 GV/m. Correspondingly, efforts are currently underway to integrate these advancements into a water-window free-electron laser (FEL) demonstration experiment.
This presentation charts a path toward an SWFA-based FEL. It will particularly address the beam dynamics challenges associated with generating bright electron bunches for FEL applications and high-charge bunches for wakefield generation. We will also describe ongoing experimental activities aimed at achieving reliable short-pulse operation of high-gradient accelerating structures and the generation of bright electron bunches. Additionally, we will discuss potential designs for accelerating structures operating in the short-pulse regime and explore options for an integrated accelerator supporting the operation of a compact FEL operating in the water-window regime.
Compact free electron laser (FEL) technology enabled by plasma-based accelerators is rapidly maturing with several milestone demonstrations in the last several years. Still, critical work is needed to bridge the gap from proof of concept experiments to reliable operation of laser plasma accelerator (LPA) driven FELs. At the BELLA Center, we have Hundred Terawatt Undulator beamline equipped with an electron beam transport section that culminates in a 4m long, strong focusing undulator. Recent efforts have produced reliable operation of a high gain FEL.
This work was supported by the U.S. Department of Energy (DOE) Office of Science, the Office of Basic Energy Sciences, and the Office of High Energy Physics, under Contract No. DE-AC02-05CH11231, and through a CRADA with Tau Systems
Laser-plasma acceleration has enormous potential to provide compact sources of ultra-short ion beams. However, several factors hamper their wider adoption, such as the low shot-to-shot stability, large beam divergence and the difficulty of high-repetition rate operation. In this talk I will outline an approach for overcoming these challenges by a novel liquid sheet target, developed at the SLAC National Accelerator Laboratory. I will report on recent experiments at the GEMINI TA2 laser facility (10 TW, 5 Hz) which demonstrated stable acceleration of few MeV proton beams with high flux and low-divergence proton beams in comparison to typical laser-accelerated ion beams. Supporting PIC simulations have shown that the presence of background vapour around the target plays an important role in the observed collimation of the proton beam. The measured proton beams are already suitable for applications requiring high proton flux and the platform can be extended to kHz repetition rates or higher laser energies extending the utility of the source to a wide range of applications in radiobiology, materials science and fundamental physics.
Currently, the Extreme Light Infrastructure – Nuclear Physics (ELI-NP) facility is running the most powerful laser in the world. The commissioning of the 10 PW laser system began at the end of 2022 and continued until recently. The first ever 10 PW shot focused on target was fired on April 2023 and since then a constant effort has been made to improve the laser performance and the experimental areas.
The high-power laser system (HPLS) is a Ti:Sa-based laser with wavelength centered at 810 nm. It has 2 arms that can deliver up to 240 J in about 23 fs at a repetition rate of a shot per minute. The maximum peak intensity achieved on target is of several $10^{22}$ Wcm$^{-2}$. Such intensity was employed to investigate the acceleration of ions via the TNSA-RPA mechanism. Several diagnostics were employed to characterize the interaction and investigate the laser performance extensively. Interesting results have been obtained, as a record high proton energy of about 150 MeV.
The laser system generally exhibits very good performances, although existing issues have been exposed, as for instance, pre-pulses in the picoseconds and nanoseconds range that prevent an optimal interaction.
Further investigation and optimization of laser-matter interaction with the 10 PW laser will be performed this year, meanwhile, some improvement in the HPLS will be also made.
Laser-driven (LD) proton sources are of interest for various applications due to their ability to produce short proton bunches with high charge. These sources can be used in biological studies investigating improvements to radiation cancer therapy. Recently, the differential sparing effect on normal tissues versus tumors using the delivery of high radiation doses >10 Gy at extremely high dose rates (DR), has received increasing attention. However, the molecular and cellular mechanisms underlying the sparing effect are not yet fully understood. To explore these mechanisms, we have implemented a beamline at the BELLA PW that delivers LD proton bunches at ultra-high instantaneous DR (UHIDR) up to 10$^8$ Gy/s. This allowed us to investigate in vivo the acute skin damage and late radiation-induced fibrosis in mouse ears after UHIDR with 10 MeV LD protons and prescribed doses of several 10s of Gy. We observed sparing of healthy mouse ear tissue after irradiations with LD proton bunches at UHIDR compared to irradiations with 300 kV x-rays at clinical dose rates and similar total dose. Recent improvements to the LD proton source, delivery beamline, and diagnostic suite have also enabled the first peptide sample irradiations to explore the FLASH effect on the molecular level. This talk will provide a summary of radiobiology research activities at the BELLA PW.
Work was supported by the U.S. DOE Office of Science, Offices of FES and HEP, and LaserNetUS under Contract No. DE-AC02-05CH11231 and a Laboratory Directed Research and Development Grant, PI A. M. Snijders.
We describe recent results from our programme to develop high-repetition-rate, GeV-scale plasma-modulated plasma accelerators (P-MoPAs).
This programme seeks to take advantage of advanced thin-disk lasers (TDLs) that can deliver joule-scale pulses, at kHz repetition rates, but with a pulse duration that is too long ($\sim 1\,\mathrm{ps}$) to drive a wakefield directly at the densities of interest. The P-MoPA concept circumvents this by modulating a single TDL pulse to form a train of short pulses that can resonantly excite a plasma wave.
A P-MoPA has three stages: (i) a modulator, in which a TDL pulse is guided in a hydrodynamic optical-field-ionized (HOFI) plasma channel and is spectrally modulated by the wake driven by a short, low-energy pulse; (ii) a compressor, which converts the spectrally-modulated drive pulse to a train of short pulses; and (iii) a resonantly-driven accelerator stage, also based on a HOFI channel.
We will present the results of simulations that establish the operating regime of P-MoPAs and demonstrate acceleration to $\sim 2.5\,\mathrm{GeV}$ with a $5\,\mathrm{J}$ drive pulse. This analysis shows that a P-MoPA can drive larger amplitude wakefields than a plasma beat-wave accelerator with the same total laser energy.
We also present the results of experiments that demonstrate resonant wakefield excitation by a train of $\sim 10$ pulses, of total energy $\sim 1\,\mathrm{J}$, in a $110\,\mathrm{mm}$ long HOFI channel. Measurements of the spectral shift of the pulse train suggest a wake amplitude in the range $3 – 10\,\mathrm{GV\,m}^{-1}$, corresponding to an accelerator stage energy gain of order $1\,\mathrm{GeV}$.
We propose a novel scheme for controlling the injection of a high-quality electron bunch into a channel-guided laser plasma accelerator. The all-optical plasma density tailoring technique allows for the generation of a tunable controlled injection structure natively within a plasma waveguide, a key requirement for efficient single-stage acceleration of multi-GeV beams of high quality. We describe a simple optical setup to form the structure and present proof-of-concept simulations showing the acceleration of a GeV electron beam with 18 pC of charge and less than 1 % energy spread using 1 J of drive laser energy.
Recently developed techniques for optical generation of low density (≤10^17 cm^(-3)), meter-scale hydrodynamic plasma waveguides in extended supersonic gas jets [1-3] have already enabled a new class of fully-optical multi-GeV laser wakefield accelerators [4,5]. Optimization of the laser wakefield acceleration (LWFA) process in these types of waveguides and plans for future, single-stage 100 GeV accelerators [6] require detailed understanding of drive laser pulse evolution over meter-scale propagation lengths. Here, we show that guided relativistically intense pulses in long, low-density plasma waveguides, appear to have a universal nonlinear behaviour, independent of whether the injected pulse is linearly mode matched to the waveguide. This behaviour can strongly influence the structure of multi-GeV electron spectra [7]. We describe key pieces of the model including plasma waveguide modal dispersion and a new mode-beating effect arising from wake excitation within narrow plasma channels.
Work supported by U.S. Department of Energy (DE-SC0015516, LaserNetUS
DE-SC0019076/FWP#SCW1668, DE-SC0011375), National Science Foundation
(PHY2010511), and Defense Advanced Research Projects Agency (DARPA) under the
Muons for Science and Security Program. E. Rockafellow supported by NSF Graduate
Research Fellowship (DGE 1840340).
Structured plasma channels are an essential technology for driving high-gradient, plasma-based acceleration and control of electron and positron beams for advanced concepts accelerators. Laser and gas technologies can permit the generation of long plasma columns known as hydrodynamic, optically-field-ionized (HOFI) channels, which feature low on-axis densities and steep walls. By carefully selecting the background gas and laser properties, one can generate narrow, tunable plasma channels for guiding high intensity laser pulses. We present on the development of 1D and 2D simulations of HOFI channels using the FLASH code, a publicly available radiation hydrodynamics code. We explore sensitivities of the channel evolution to laser profile, intensity, and background gas conditions. We examine efforts to benchmark these simulations against experimental measurements of plasma channels. Lastly, we discuss ongoing work to couple these tools to community PIC models to capture variations in initial conditions and subsequent coupling for laser wakefield accelerator applications.
Hydrodynamic plasma waveguides initiated by optical field ionization (OFI) have recently become a key component of multi-GeV laser wakefield accelerators [1–4], We present comprehensive experimental and simulation-based characterization, applicable both to current multi-GeV experiments and future 100 GeV-scale laser plasma accelerators. Crucial to the simulations is the correct modeling of intense Bessel beam interaction with meter-scale gas targets [4], the results of which are used as initial conditions for hydrodynamic simulations [5,6]. The simulations are in good agreement with our experiments measuring plasma and neutral hydrogen density profiles using two-color short pulse interferometry, enabling realistic determination of the guided mode structure for application to laser-driven plasma accelerator design [7].
The authors thank Scott Wilks and Brendan Reagan for useful discussions. This work was supported by the U.S. Department of Energy (DE-SC0015516, LaserNetUS
DE-SC0019076/FWP#SCW1668, and DE-SC0011375), the National Science Foundation (PHY2010511), and the Defense Advanced Research Projects Agency (DARPA) under the Muons for Science and Security Program. E. Rockafellow is supported by a NSF Graduate Research Fellowship (DGE 1840340).
[1] N. Lemos et al, Phys. Plasmas 20, 063102 (2013).
[2] R. J. Shalloo et al, Phys. Rev. E 97, 053203 (2018).
[3] B. Miao et al, Phys. Rev. Lett. 125, 074801 (2020).
[4] L. Feder et al, Phys. Rev. Res. 2, 43173 (2020).
[5] D. Gordon et al, NRL Memo. Rep. 6706 (2006).
[6] S. M. Mewes et al, Phys. Rev. Res. 5, (2023).
[7] B. Miao et al., Under review, arXiv:2404.13632(2024)
Laser wakefield accelerators (LWFA) have long promised to revolutionize particle acceleration by shrinking facility size and cost by orders of magnitude. Despite twenty years of experiments however, we do not understand the performance envelope of LWFAs. Experiments and simulations demonstrate a wide range of possible operating points, ranging from high-charge beams to high-energy beams. Models tend to provide rough estimates of electron beam energy only and a rough guide for design only in this parameter. To address this gap, we analyze a large set of the published experimental data to estimate a general performance envelope for LWFAs. We find that laser wakefield accelerators exhibit somewhat better scaling of overall input-to-output energy efficiency than radio-frequency accelerators. To the extent possible, we also compare experimental choices and outcomes to models in the literature.
The FLASHForward experiment at DESY uses the FEL-quality electron bunches from the FLASH linac to perform research into the plasma wakefield acceleration of high-brightness electron bunches. This talk will provide an overview of recent results in four areas: beam quality preservation, energy efficient acceleration, high-brightness internal injection and plasma evolution studies. By precisely controlling the transverse properties of the witness bunch while simultaneously loading the wakefield longitudinally, we were able to demonstrate the preservation of the witness-bunch emittance during plasma acceleration for the first time. The emittance was preserved at the level of 2.8 mm.mrad while also maintaining > 20% instantaneous energy transfer efficiency. To improve the overall energy transfer efficiency, the driver bunch must be depleted. We will present the latest results on driver energy depletion, a novel longitudinally resolved efficiency-monitor technique and the development of plasma cells for higher witness-bunch energy gain. Brief updates will also be given on the status of density-downramp injection experiments delivering highly reproducible mm-mrad emittance electron bunches with per-cent-level energy spreads, and the combination of experimental and simulation techniques to probe the plasma evolution in our plasma cells.
The Facility for Advanced Accelerator Experimental Tests II (FACET-II) has successfully completed its first plasma wakefield acceleration (PWFA) experiments using the two-bunch beam delivery configuration. In these initial studies, a drive and witness pair of bunches were produced at the photocathode injector, co-accelerated, and transported to the experimental area. Two plasma sources were employed for PWFA: either a 40 cm long lithium plasma oven, or a multi-meter long hydrogen static fill, both of which were beam-ionized via the drive bunch. We will present preliminary results demonstrating multi-GeV energy gain of the witness bunch, measurements of the energy spread and emittance of the accelerated charge, along with comparative performance from the two plasma sources. Additionally, we will discuss plans for refining the two bunch delivery to enhance the capture and acceleration of the witness bunch.
Plasma wakefield accelerator experiments at FACET-II aim to double the energy of a 10GeV witness beam while maintaining a low energy spread and preserving the beam’s emittance. Achieving energy doubling requires drive-to-wake energy transfer efficiencies of 60-80% while maintaining the structure and amplitude of the wakefields. We present the current progress towards maximizing the drive-plasma interaction in several different plasma sources.
In plasma wakefield accelerators (PWFA) we usually assume that the plasma is infinitely wide, a property generally desirable for high-quality high-efficiency acceleration of electrons in the blowout regime of PWFA. Finite-width plasmas have gained a particular attention due to their potential applications for light sources and positron acceleration schemes. When the plasma is narrow transversely, blown-out electrons no longer experience a sufficient restoring force from the ions to be pulled back to the axis. Due to this lack of returning plasma electrons, an ion channel is formed behind the beam without an oscillating wakefield, a regime referred to as the wakeless regime particularly interesting for light sources by providing a purely focusing channel. Right at the transition between standard PWFA and wakeless when plasma radius approximately matches blowout radius, plasma electrons return to the axis but their return position is spread longitudinally, a scheme with high potential for positron acceleration.
At SLAC, we showed that beam-ionized helium plasma can sustain standard PWFA or wakeless regime. The plasma is narrow transversely due to the very high ionization potential of He. I will present observations from FACET and FACET-II where the wakeless nature in beam-ionized helium plasma is revealed by the lack of accelerating field and accelerated electrons, as well as how we can transition between standard PWFA and wakeless by controlling the beam compression and peak current. The data is supported by particle-in-cell simulations that confirm that the beam current is a critical parameter to transition between these two regimes.
The wakefield accelerators, based on THz and mm-wave structures, is an active area of research aiming at a severalfold higher accelerating field and better wall plug power efficiency than conventional linear accelerators. Concurrently to accelerator development additional components are required for constant beam parameters and position monitoring. As the electron beam passes through a metal waveguide with corrugated walls a sub-THz Cherenkov radiation is formed. Using different components (modes) of this radiation one can derive the needed beam parameters. At the same time detecting sub-THz signal has its own challenges both in handling time resolution and peak amplitude.
In this work we report the evaluation results of a candidate passive THz detectors, based on the gate-modulation of the conductance channel by the incoming radiation in field effect transistor (FETs), supplied by TeraSense. The first set of measurements was performed on a bench in the millimeter wave laboratory at the Advanced Light Source (APS) of the Argonne National Laboratory and the second set of measurements was performed using the 4.5 MeV RadiaBeam photoinjector and the 10 cm long corrugated wave guide. The design and performance of the optical system including the polymethyl-pentene (TPX)-based lens and vacuum window used in the electron beam measurements is also described.
Few-fs electron bunches from wakefield accelerators possess a strong micro-bunched component, which can be critical in seeding free electron lasers. Spectrally multiplexed near-field (NF) imaging of the strong coherent optical transition radiation (COTR) that these bunches emit at wavelengths comparable in size to the bunch‘s internal features enables single-shot recovery of the bunch‘s coherently-radiating structure, using algorithms similar to those used in ptychography and coherent diffraction imaging. The multi-spectral image sets and reconstructed bunch shapes vary widely for different methods of injecting electrons into an LWFA, and will be important in designing and monitoring FELs based on LWFAs. Adding multi-spectral far-field (FF) imaging expands the diagnostic capabilities by providing transverse momentum information. Here we present experimental results of simultaneously measured multispectral NF and FF COTR from wakefield accelerated electron bunches and as well as a preliminary framework to derive a 5D phase space from such data.
We report on the ongoing commissioning of a prototype Electro-Optic Sampling Beam Position Monitor (EOS-BPM) at the FACET-II Facility at SLAC National Accelerator Laboratory. In EOS-BPM, a birefringence is induced in two electro-optic crystals on either side of the electron beam's trajectory as it passes by. Laser pulses traveling through each crystal pick up a spacially encoded polarization which is detected. The signal from each crystal provides a single-shot, non-destructive diagnostic of the relative time of arrival of the beam and, in two bunch operation, the longitudinal separation between the drive and witness bunches. By comparing the relative strengths and locations of the signals on each crystal, the instrument can in principle measure the transverse $x$ position and angle of both bunches. We discuss how the installed prototype is currently being employed at FACET-II for plasma acceleration experiments and two bunch commissioning. We present the results of preliminary attempt to commission the beam position and angle monitoring functionality of the prototype. Finally, we discuss engineering improvements to the currently installed instrument as well as work designing and building an improved prototype capable of measuring beam position and angle in both transverse directions.
We report a single-shot diagnosis of electron energy evolution in a curved laser wakefield accelerator by using the streaked betatron x rays. The streaking of the betatron x rays was realized by launching a laser pulse into a plasma with a transverse density gradient. In such a plasma, laser wavefront tilt develops gradually due to phase velocity differences in different plasma densities. The wavefront tilt leads to a parabolic trajectory of the plasma wakefield and hence the accelerated electron beam, which leads to an angular streaking of the emitted betatron radiation. In this way, the temporal evolution of the betatron x-ray spectra will be converted into an angular ``streak,” i.e., having an energy-angle correlation. By controlling the plasma density and the density gradient, we realized the steering of the laser driver, electron beam and betatron x rays simultaneously. Moreover, we observed an energy-angle correlation of the streaked betatron x rays and utilized it in diagnosing the electron acceleration process in a single-shot mode. Our work could also find applications in advanced control of laser beam and particle propagation. The angular streaked betatron x ray has an intrinsic spatiotemporal correlation, which makes it a promising tool for single-shot pump-probe applications.
The direction of particle accelerator development is ever increasing beam quality, currents, and repetition rates. Advanced control techniques using machine learning are required for the optimization and operation of such accelerators. These techniques greatly benefit from having single-shot beam measurements. However, high intensity beams poses a challenge for traditional interceptive diagnostics due to the mutual destruction of both the beam and the diagnostic.
An alternative approach is to infer beam parameters non-invasively from the synchrotron radiation emitted in bending magnets. In this talk, we will discuss the development of such a diagnostic at FACET-II. Inferring the beam distribution from a measured radiation pattern is a complex and computationally expensive task. To address these challenges we use differential simulations and computer vision techniques. This enables both fast inference and uncertainty quantification of the beam parameters.
The ongoing Plasma-driven Attosecond X-ray source experiment (PAX) at FACET-II aims to produce coherent soft X-ray pulses of attosecond duration using a Plasma Wakefield Accelerator [1]. These kinds of X-ray pulses can be used to study chemical processes where attosecond-scale electron motion is important. For this first stage of the experiment, PAX plans to demonstrate that <100 nm bunch length electron beams can be generated using the 10 GeV beam accelerated in the FACET-II linac and using the plasma cell to give it a percent-per-micron chirp. The strongly chirped beam is then compressed in a weak chicane to sub-100nm length, producing CSR in the final chicane magnet at wavelengths as low as 10s of nm. In this contribution we describe the developments in commissioning the experiment as well as the expected results.
Additionally, we describe a future iteration of the experiment in which short undulators are used to drive coherent harmonic generation to produce attosecond gigawatt X-ray pulses at 2 and 0.4 nm, with lengths comparable to the shortest attosecond pulses ever measured at 2 nm using HHG.
[1] C. Emma, X.Xu et al APL Photonics 6, 076107 (2021)
At the last International Free-electron Laser Conference, there were two reports in the novel applications session of initial free-electron laser (FEL) experiments with laser-driven wakefield accelerator beams as drivers at 274 and 27 nm, respectively. These experiments in single-pass, self-amplified spontaneous emission mode (SASE) showed gain, but not power saturation. Only the 27-nm case exhibited exponential gain. The investigators speculated that these were steps towards future compact x-ray FELs. However, basic evaluations of the critical Pierce parameter, rho, used in SASE models show there are significant beam-quality challenges to be met to achieve enough gain to reach saturation at shorter x-ray wavelengths. Some of the key parameters of charge, transverse emittance, energy spread, and peak current will be assessed in the context of these first two experiments performed in Germany and China.
The propagating density gradients of a plasma wakefield may be used to frequency upshift a trailing witness laser pulse, a process known as `photon acceleration'. Using a beam driver, shifts limited only by the particle beam energy are possible by finding appropriate phase-matching conditions with a tailored density gradient. The resulting extreme intensity XUV laser light demonstrated in quasi-3D simulations may be of interest for applications. In particular, we examine the use of such light in laser-electron beam collisions where perturbative quantum electrodynamics theory becomes invalid. While optical wavelengths in conventional laser-electron beam collisions will allow for quantum nonlinearities, $\chi_e> 10$, we show that the use of XUV light may allow us to push to $\chi_e>100$. Theory and particle-in-cell simulations are used to predict the scattered photon spectra from these interactions and to find potential diagnostics for the measurement of such very high-$\chi$ effects.
Laser-driven free-electron lasers (LDFELs) replace magnetic undulators with the electromagnetic field of a laser pulse. Because the undulator period is half the wavelength of the laser pulse, LDFELs can amplify x rays to saturation using lower electron energies and over shorter interaction lengths than a conventional free-electron laser. Here we show that a flying-focus pulse substantially reduces the energy required to reach saturation in an LDFEL by providing a highly uniform, high-intensity field over the entire interaction length. The flying-focus pulse features an intensity peak that travels in the opposite direction of its phase fronts. This enables an LDFEL configuration where an electron beam collides head-on with the phase fronts and experiences a near-constant undulator strength as it co-propagates with the intensity peak. Three-dimensional simulations of this configuration demonstrate the generation of megawatts of coherent x-ray radiation with 20 times less energy than a conventional laser pulse.
This material is based upon work supported by the Department of Energy [National Nuclear Security Administration] University of Rochester “National Inertial Confinement Fusion Program” under Award Number DE-NA0004144 and Department of Energy Office of Science under Award Number DE-SC0021057.
Extreme ultraviolet (XUV) light sources allow for the probing of bound electron dynamics on attosecond scales, interrogation of high-energy-density and warm dense matter, photolithography of nanometer-scale features, and access to novel regimes of strong-field quantum electrodynamics. Despite the importance of these applications, coherent XUV light sources remain relatively rare, and those that do exist are limited in their peak intensity and spatio-polarization structure. Here, we demonstrate that photon acceleration of optical laser pulses in the moving density gradient of an electron-beam-driven plasma wave can produce relativistically intense XUV laser pulses that preserve the spatio-polarization structure of the original pulse. Quasi-3D, boosted-frame particle-in-cell simulations show the formation of XUV attosecond vector vortex pulses with ~30-nm wavelengths, nearly flat phase fronts, and intensities exceeding $10^{21}$ W/cm$^2$.
Laser wakefield accelerator-driven betatron x-rays are bright, broadband synchrotron-like emission with micrometer-scale source size and sub-picosecond duration. Betatron x-rays provide a new avenue for high-resolution, high-throughput imaging of additively manufactured (AM) materials. AM alloys are commonly used in aerospace and automotive industries due to high strength and stiffness to weight ratios. Using the Advanced Laser Light Source betatron beamline in Qc, Canada, we performed high-resolution 3D tomography of AM aluminum-silicon-magnesium (AlSi10Mg) alloys under tensile load. Prior to x-ray tomography, the betatron source was optimized from a Helium-Nitrogen gas jet for x-ray imaging at 2.5 Hz. X-ray tomography of pores in AlSi10Mg samples over 180° with 3° increments at 2.5 Hz were obtained in 72 minutes. This rate of tomography enabled visualization of micrometer pore dynamics under different tensile loads prior to fracture. To improve the data acquisition rate, we require enhancement of betatron flux and source stability. Accordingly, we have further optimized the betatron source using a 7 mm 3D printed gas cell, leading to ~ 6 times higher flux and ~ 20 times reduced pointing fluctuation compared to the gas jet targets. We estimate that using gas cell targets, we could perform 180° tomography at 3° increments in approximately 15 minutes. Upcoming experiments will strengthen our original studies by providing additional porosity evolution data to validate degradation models and thereby, advancing our understanding of ductile fractures in AM alloys.
SWFA (structure wakefield accelerator) provides a viable approach to the TeV class linear collider, but significant challenges remain. The recent P5 report recommended development of a wakefield technology based 10TeV collider design in next 5 years. In this presentation, the current status of SWFA for LC will be presented. The potential contribution of SWFA technologies to the unified wakefield collider will be discussed.
Laser-driven plasma accelerators have demonstrated ultra-high accelerating gradients, offering the potential to reduce the size and cost of a future energy-frontier linear collider. In this presentation, I will discuss the design considerations for the application of laser-driven plasma-based accelerator technology for a multi-TeV linear collider. Plasma accelerators naturally accelerate short bunches using large longitudinal and transverse wakefields in plasma, and this presents unique beam dynamics challenges. Key to the realization of the collider application is the development of high average and high peak power laser systems, operating with high efficiency. Coherent combination of fiber lasers is a promising solution to achieve high average and high peak power lasers suitable for high-energy physics applications. I will describe recent progress and outline the R&D path toward a collider based on laser-plasma accelerator technology.
In this presentations we will review the design approaches for Beam Delivery and Machine Detector Interface for advanced colliders, starting from designs of classical colliders, and discussing what design assumptions need to be revisited and how, in order to arrive to an optimal design suitable for next generation concepts.
In this talk we will consider possible pathways for the upgrade of a linear Higgs factory to High Energy.
FACET-II is an accelerator test beam facility that delivers high-charge, ultra-short bunches with nC-level charge. FACET also supports a multi-TW laser system that is used to ionize plasmas or collide with electron beams for strong-field QED experiments. Because FACET-II is a test beam facility, both the beam parameters and experimental area can be configured to meet the needs of the experiment. We propose to operate FACET-II with long (mm-scale) bunches with nC charge in collision with long (ps-scale) laser pulses to study Compton polarimetry, laser control of bunch intensity, and laser-based collimation in support of FCC-ee R&D. We seek opportunities to improve the performance of detectors for Compton polarimetry and the reliability of the Compton backscatter (CBS) interactions for the bunch intensity control and collimation studies. Our proposed studies leverage the E320 strong-field QED experimental apparatus and detectors to facilitate these measurements.
This talk will cover proposals for beam driven, plasma-based (PWFA) colliders both past and present. It will cover the proposed systems and future work as written. It will also review community feedback and challenges, some unique to PWFA. The goal is a high degree of audience discussion of the status of PWFA and the road to a collider.
The successful operation of future e+ e- linear colliders (LC) critically relies on the ability to tightly focus beams at the interaction point to achieve high luminosities. With spot sizes expected to reach the nanometer scale in TeV LC, traditional beam delivery systems face challenges due to chromatic effects and the requirement of small emittance. To overcome these challenges, the concept of adiabatic plasma lenses for the electron arm of the collider has emerged as a potential solution. In an azimuthally symmetric passive adiabatic plasma lens, a plasma wave wake is excited by a particle beam and a trailing beam surfs on the wake, experiencing a linear focusing force of $m\omega_p^2 r/2$, which is proportional to the plasma density. An adiabatic plasma upramp is designed so that the focusing force on the trailing beam slowly increases during propagation. However, the tightly focused beam of LC can induce ion motion within the beam, an aspect that has not been extensively investigated in previous studies of adiabatic lenses. We propose designs of adiabatic plasma lens for final focus of the electron arm of 2TeV-15TeV COM LC using the advanced simulation tools, QuickPIC with adaptive mesh refinement and QPAD. Furthermore, we show that ion motion on the trailing beam will increase the strength of the focusing force, which can relax the stringent emittance requirements for the LC design. Additionally, we examine how an asymmetric drive beam can add asymmetry to the witness beam, thereby possibly reducing beamstrahlung during e-e- or e+e- collision.
In a series of experiments at OMEGA EP facility, we explore potential of petawatt 1-um laser-driven ion acceleration in two-photon polymerization 3D laser printed microstructures. We tested two types of accelerators made of acrylic log-pile organized wire and stochastic non-periodic wire microstructures. We find that enhanced target normal sheath acceleration mechanism is responsible for detected ~80-110 MeV protons with a high conversion efficiency reaching ≥8%. The key advantage of a relatively thick 10-50 um log-pile (stochastic) wire structure is efficient coupling of the laser into a flux of hot electrons in the target's front and formation of an overdense, wire-related, microplasma surrounded in voids by a low-density plasma sustaining sheath field at the back on a few picoseconds time scale. Additional electron heating in such a hybrid plasma resulted in generation of a stream of hot electrons in forward direction with an electron temperature, Thot≥20MeV and with the maximum electron energy about 150 MeV much above the ponderomotive energy. We observed no difference in proton beam laminarity and energy between a free-standing log-pile structure and the same structure printed in front of the 2 um flat foil. 3D printed multilayer microstructures represent a robust platform for reproducible ion acceleration relatively immune to the picosecond and nanosecond laser prepulses. It may become a viable alternative to nanofoils in generation of energetic ion beams that doesn’t require high-contrast laser pulses. Modeling reveals that such designer accelerators are promising for production of 60-200 MeV proton beams with a high-peak-current for advanced radiotherapy application.
Energetic particles, including electrons, ions and secondary particles, are produced by directing an intense laser pulse at a target material. The laser-driven ion beam may find applications in inertial fusion or high-resolution images of both static and dynamic objects in next-generation radiography to probe materials and plasmas in extreme environments. To scale up ion beam production suitable for these applications, we have conducted experiments using a 0.5kJ sub-ps laser at the Omega-EP laser facility to characterize the laser-driven ion beam from a variety of solid targets, including CH/CD/Kapton sub-micron thin films, low-density CD foams and flat CH foil targets of micron-scale thickness, encompassing ion acceleration regimes including Target Normal Sheath Acceleration (TNSA), Radiation Pressure Acceleration (RPA) or Collisionless Shock Acceleration (CSA), and Relativistic Transparency (RT). Ion acceleration with/without Compound Parabolic Concentrator (CPC) cone have also been compared. We obtained beam spectra and spatial source profiles, and found that ~700-800nm foil target achieved the best ion yield among the targets tested. Preliminary static and dynamic radiography were also conducted using these laser-driven ion beams. The different characteristics of the ion beams produced from these targets will be summarized and compared with simulations of preplasma formation and main pulse interaction with the target, and understandings/scaling from the literature.
Characteristics of ions accelerated in laser plasma depend on the parameters of the irradiating laser pulse, especially on its temporal contrast and pulse duration. The latter can be varied also by introducing chirp to the spectral phase of the pulse. Recent studies have revealed such an effect with the use of 100 TW peak power lasers. However, the temporal contrast was probably not high enough in such an experiments for providing an unambiguous explanation.
We have carried out series of systematic experiments to study the dependence of laser-accelerated deuterons on the temporal shape of the laser pulses. The TW peak power, 12 fs laser pulses of the SEA laser in ELI-ALPS exhibit a temporal contrast better than 10^11 at the leading edge. A DAZZLER varied both the linear (GDD) and nonlinear chirp (TOD) on a broad range.
Two types of ultrathin targets were investigated, both promising for laser-based neutron generation: deuterated foils and heavy water leafs. The cut-off energy of the ions and the maximum total energy of an ion bunch were measured by Thomson ion spectrometers. The studies revealed that the least cutoff and yield were achieved with transform limited pulses, while the highest values were obtained with pulses of negative GDD. However, at zero GDD, the deuteron yield and cutoff energy varied a factor of two, depending on the sign and the amount of TOD. Such phenomena, supported by 2D PIC simulations, can be explained by self-induced transparency and post-acceleration.
The concept of the Travelling Wave Tube (TWT) was conceived in 1947, followed by analytical models in the 1950s. The growing interest of this system takes source with the domain of high power and high frequency microwave devices such as the gyrotrons, the relativistic travelling wave tubes or the free-electron lasers. On the other hand, Target Normal Sheath Acceleration (TNSA) is currently one of the most dynamic research domains due to its conpactness and numerous applications such as isochoric heating, isotope or neutron production, plasma radiography, and nuclear fusion in a fast ignition scheme. The concept involves interacting a high-intensity laser beam with a solid target. However, the angular divergence of TNSA is still too high, and the energy distribution of protons is poorly controlled, limiting the application possibilities.
In this context, the idea to implement a system coupled to TNSA was conceived to post-accelerate and focus the proton beam, termed the helical coil. The concept involves retrieving a discharge current, created by the laser-plasma interaction, using a helix. The physics of current propagation in this helix is analogous to TWT. However this concept is not optimize. This is why, we propose a new analytical model with an implementation of a tube and a variation on the helical coil geometry to permit applications. During this presentation, we will introduce our theoretical model and present some significant results of proton spectra get by simulations and some possible applicationd sich as radioisotope production or isochoric heating.
Laser-driven ion accelerators (LDIAs) generate high-intensity beams, offering immense potential across various applications, including investigating ultra-high dose rate radiobiological research. The significant beam divergence of laser-driven proton beams at the source requires capture and transport of these beams to maintain a high particle intensity at the sample site located outside the main target chamber. At the BELLA Center's iP2 beamline, we have deployed two beam transport configurations, leveraging permanent magnets for compactness, to reliably deliver up to 30 MeV protons to biological samples at high particle intensities. In conjunction with these setups, a comprehensive suite of diagnostic tools was implemented for dosimetry tasks, including multiple integrating current transformers (ICTs) for indirect online dose measurements and calibrated radiochromic films (RCFs) to measure the dose distribution and calibrate the ICTs. With the use of Monte Carlo simulations of the beamline, we achieve accurate dose estimates applied to the samples, while accounting for the linear energy transfer (LET)-dependent response of RCFs. The proton beam transport was successfully used for in vivo biological sample irradiations and is available to future users of BELLA iP2.
Work was supported by the U.S. DOE Office of Science, Offices of FES and HEP under Contract No. DE-AC02-05CH11231, and by LaserNetUS. S. Hakimi was supported by the U.S. DOE FES Postdoctoral Research Program administered by the Oak Ridge Institute for Science and Education (ORISE) under Contract No. DE-SC0014664. B. Stassel was supported by the U.S. DOE, Office of WDTS, Graduate Student Research (SCGSR) program under Contract No. DE‐SC0014664.
Contributors with posters provide a short introduction/advert for their posters.
Next-generation accelerator concepts, which hinge on the precise shaping of beam distributions, demand equally precise diagnostic methods capable of reconstructing beam distributions within 6-dimensional position-momentum spaces. However, the characterization of intricate features within 6-dimensional beam distributions using current diagnostic techniques necessitates a substantial number of measurements, using many hours of valuable beam time. Novel phase space reconstruction techniques are needed to reduce the number of measurements required to reconstruct detailed, high-dimensional beam features in order to resolve complex beam phenomena, and as feedback in precision beam shaping applications. In this study, we present a novel approach to reconstructing detailed 6-dimensional phase space distributions from experimental measurements using generative machine learning and differentiable beam dynamics simulations. We demonstrate that this approach can be used to resolve 6-dimensional phase space distributions from scratch, using basic beam manipulations and as few as 20 2-dimensional measurements of the beam profile. We also demonstrate an application of the reconstruction method in an experimental setting at the Argonne Wakefield Accelerator, where it is able to reconstruct the beam distribution and accurately predict previously unseen measurements 75x faster than previous methods.
Coherent synchrotron radiation (CSR) is a limiting effect in linear accelerators with dispersive elements due to its contribution to projected transverse emittance growth. This effect becomes a limitation for highly compressed beams. Even though CSR-induced projected emittance growth has been widely studied, conventional measurement techniques are not detailed enough to resolve the multi-dimensional structure of the beam, namely the different rotations of transverse phase space slices throughout the longitudinal coordinate. In this work, we simulate the reconstruction of a CSR-affected beam after a double dogleg at the Argonne Wakefield Accelerator Facility by using our generative-model-based six-dimensional phase space reconstruction method. Additionally, we study the current limitations of the phase space reconstruction method and perform an analysis of its accuracy and precision in simulated cases in preparation for the experimental demonstration.
Free electron lasers (FEL) are powerful scientific tools for a wide variety of applications which require bright, coherent X-ray light. FELs require electron beams with high requirements on brightness, as well as alignment and matching into the undulators. At the Hundred Terawatt Undulator (HTU) system at the BELLA Center, we are aiming to demonstrate a compact Laser-Plasma Accelerator (LPA)-driven FEL using 100-500 MeV electron beams from a gas jet target. Knowledge of the electron beam phase space prior to the undulator is key for achieving good FEL operation, and creative beam diagnostics can greatly improve our understanding of the electron beams generated in the compact LPA.
We present progress at adapting a machine-learning approach to reconstructing the transverse electron beam phase space using images of the electron beam in a quadrupole magnet scan. While this algorithm has previously been used with great success for electron beams produced in conventional accelerators, here we perform reconstructions using beams injected from an LPA with considerably more shot-to-shot jitter. Additionally, by including a dipole magnetic spectrometer we can improve this 4D transverse reconstruction to a 5D reconstruction using the electron beam's energy spectrum.
This work was supported by the U.S. Department of Energy (DOE) Office of Science, the Office of Basic Energy Sciences, and the Office of High Energy Physics, under Contract No. DE-AC02-05CH11231, and through a CRADA with Tau Systems.
While the well-known transition radiation usually has negligible impact on high-energy beams, high-current beams such as those from the FACET-II facility can be strongly self-focused by the near field of transition radiation when passing through multiple closely spaced foils. This extreme focusing of high-energy beams opens a new physics frontier with unprecedented densities, potentially approaching that of a solid. The E-332 experiment at SLAC National Accelerator Laboratory has reached a first critical milestone with the experimental demonstration of a collective interaction between a high-energy beam and a multifoil target, whereby the focusing nature of the interaction has been evidenced. This major experimental achievement and future plans will be presented.
Reducing the size of free-electron laser (FEL) light sources relies on producing bright electron beams and preserving the beam brightness during acceleration and beam manipulation. The laser-assisted bunch compression (LABC) scheme is a promising technique to significantly enhance the beam current for a very low emittance beam. We explore the application of the LABC scheme to a compact FEL based on a two-beam wakefield acceleration scheme under study at Argonne National Laboratory (ANL). Our beam dynamics simulations were performed using the large-scale self-consistent LW3D code, which accounts for the impact of coherent synchrotron radiation (CSR) on the beam. The overall bunch-compression strategy supporting the generation of high-current bunches for an FEL operating in the water window is presented.
We report on the achievements and challenges on high repetition rate lasers used as drivers for electron or proton acceleration. We recently demonstrated 700TW at 10Hz repetition, based on a new generation of high repetition rate pump lasers. This system under comissioning is expected to reach 2PW at 10Hz, opening the way to high flux GeV electron sources, or >100MeV proton sources. Moreover, modern electron accelerators require even higher repetition rate, from 100Hz to 1kHz. We will present the challenges and ongoing developments in Amplitude on 100Hz to 1kHz multi-Joule class pump lasers, as well as thermal management of the main amplifier and compressor. Diagnostics and active feedback loops are also key success factors in order to ensure high stability electron or proton sources in the near future.
These high repetition rate laser drivers are expected to pave the way to industrial or medical applications through X-ray imaging using betatron radiation, bremstrahlung or all-optical Inverse-Compton Scattering, as well as particle therapy using electron or proton sources.
Laser plasma accelerators are poised to reach electron energies of 10-100 GeV and this new regime will open novel applications such as the production of heavy particles including muons. Electrons with energies exceeding twice the rest mass of a muon (211 MeV/c2) can initiate muon generation through the Bethe-Heitler pair production process. This talk will present work on behalf of a multi-institution collaboration, Intense and Compact Muon Sources for Science and Security (ICMuS2), that aims to develop the capability to generate and detect muons using high energy and high charge electron beams, primarily at Colorado State University’s ALEPH laser [1]. The electron acceleration method uses an optically formed plasma waveguide developed by University of Maryland [2,3]. Preliminary results from first of their kind experiments will be discussed along with plans for implementing the platform at the ELI-Beamlines Facility in the Czech Republic. We will also present progress on next-generation laser development research that will enable high average flux operations and system engineering to deploy such a design.
This work was supported by DARPA under the Muons for Science and Security (MuS2) Program and performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under contract DE-AC52-07NA27344.
LLNL-ABS-860513
Direct Laser Acceleration (DLA) of electrons is a mechanism for superponderomotive energy gain during relativistically intense laser-plasma interactions. As laser facilities reach multi-petawatt powers, DLA will be increasingly important as the main energy exchange mode between the laser and the plasma and create a route to generating high charge, highly-relativistic, broad-spectrum electron beams. Applications of DLA are for bright directional sources of x-rays, or for secondary interactions to create Bremsstrahlung-photons or positrons. The ponderomotive force of the laser pulse acts on the plasma to form a channel with transverse electric and azimuthal magnetic fields that enable energy exchange from the laser to the electrons. We investigate DLA using experiments performed at the OMEGA EP laser facility, particle-in-cell simulations [H Tang et al. New J. Phys. 26 053010 (2024)] and through test particle simulations and theory [R Babjak, et al. PRL, 132, 125001 (2024), AV Arefiev. et al. PoP, 31, 023106 (2024)]. New insights include the importance of laser focal spot size, the significance of the modulation of the experienced laser frequency for the betatron and high-order resonances, and a new mechanism that generates a bright, backward x-ray beam from these interactions [I-L Yeh, et al. arXiv: 2406.04489 (2024)].
Acknowledgements: Supported by the NNSA under Award Number DE-NA0004030. Experiments conducted at the Laboratory for Laser Energetics, beam time through the National Laser Users’ Facility (NLUF) Program supported by DOE/NNSA. The OSIRIS Consortium, consisting of UCLA and IST (Lisbon, Portugal) provided access to the OSIRIS 4.0 framework. Work supported by NSF ACI-1339893.
Direct laser acceleration (DLA) can generate superponderomotive energy electrons to hundreds of MeV, along with secondary particles and radiation, through the interaction of high-intensity picosecond laser pulses with underdense plasma. As a complex and dynamic process, the DLA electron acceleration can be affected by a number of factors, such as the laser focusing geometries [H Tang et al. New J. Phys. 26 053010 (2024)]. To better understand the DLA interaction and optimize the experimental conditions, our recent experiments performed on the OMEGA EP facility using apodized beams and supersonic gas nozzle targets investigated the sensitivity of the DLA process to the gradient of the plasma density ramps. 2D particle-in-cell OSIRIS simulations replicated the interaction with different plasma density profiles, providing insight into the laser channel creation, laser field evolution, as well as the unexpected effect of the sheath fields on the corresponding electron dynamics. Our results identify an optimal plasma density gradient and offer a path towards optimizing DLA conditions.
High-brightness, ultra-high peak current electron beams are of significant interest to applications including high-energy colliders, strong field Quantum Electrodynamics, and laboratory astrophysics. Despite such interest, compressing tightly-focused electron beams to attosecond pulse durations and mega-amp peak currents while preserving beam quality remains a challenge. Increased beam brightness amplifies collective effects such as Coherent Synchrotron Radiation, leading to beam degradation and limiting maximum possible compression. To achieve extreme beams while mitigating these effects, we introduce a large energy chirp to the beam followed by compression in a chicane with weak magnetic fields. We present simulations that explore the generation of these beams using the large electric field gradients present in plasma wakefields, which can produce chirps orders of magnitude larger than those found in conventional RF accelerators. The optimal beam and plasma conditions are investigated for different applications, with the objective of experimentally demonstrating this technique at the FACET-II facility at SLAC National Accelerator Laboratory. The trade-offs in beam parameters are explored with limitations on achievable final beam brightness evaluated. Insights gained from this study will help design the next-generation of high-brightness beams for new frontiers in scientific research.
The E-320 experiment at SLAC FACET-II aims to investigate Quantum Electrodynamics (QED) in the strong-field regime.
By colliding 10 GeV, high-quality electron beams with 10 TW NIR laser pulses it is aspired to probe the QED critical (Schwinger) intensity of 10E29 Wcm-2 in the electron rest frame.
In this regime, characterized by X = E/Ecr>1, quantum corrections to classical synchrotron radiation become important and the probability for electron-positron pair production is no longer exponentially suppressed [1-3].
A central objective of E-320 is to observe the transition from the perturbative (a0^2<<1) to the non-perturbative regime (a0^2>>1), characterized by the intensity parameter a0, while quantum effects are important (i.e., X ~ 1 ).
Here, qualitative changes are expected to be observed, such as e.g. a substantial red shift of the Compton edges in the electron or photon spectrum and eventually a transition to a quasi-continuous spectrum. We will report on recent progress and results in the E-320 research program as well as future plans and development efforts.
[1] A. Fedotov et al., Phys. Rep. (2023)
[2] A. Gonoskov et al., Rev. Mod. Phys. (2022)
[3] A. Di Piazza et al., Rev. Mod. Phys. (2012)
[4] C. Clarke et al., LINAC2022 (2022)
Beam-driven plasma wakefield acceleration(PWFA) has shown great potential to be the basis for future linear colliders(LCs).PWFA can achieve high acceleration gradients with high energy transfer efficiency while maintaining low energy spread.For linear collider applications and designs,the witness beam transverse spot sizes and emittances are on the order of hundreds of nanometers with charges around a nanoCoulomb,and would be accelerated over many stages.These beam parameters will cause the ions to collapse during the transit time of the beam. Mehrling et al.[1] and Hildebrand et al.[2] showed hosing of the witness beam is suppressed in this regime due to the nonlinear focusing force due to the ion collapse.We show the witness beam can be realigned with the drive beam if there is sufficient ion motion caused by the drive beam. Zhao et al.[3] recently showed quasi-adiabatic density ramps at the entrance and exit of the plasma can match LC-class beams in the presence of ion motion with emittance preservation.We combine these ideas into a single stage of a PWFA-LC where the witness beam is realigned with only ∼5% emittance growth,energy spread limited to <1%,and energy transfer efficiency exceeding ∼50%.
[1] Mehrling et al.,“Suppression of beam hosing in plasma accelerators with ion motion”, PRL 121, 264802 (2018)
[2] Hildebrand et al.,“Mitigation techniques of witness beam hosing in plasma-based acceleration”, Proceedings of the Advanced Accelerator Conference,Breckenridge, CO (2018).
[3] Zhao et al.,“Emittance preservation in the presence of ion motion for low-to-high energy stages of a plasma based accelerator”,Physics Review Accelerators and Beams 26,121301 (2023)
Laser ionized plasma sources for plasma wakefield accelerators (PWFA) offer numerous advantages, including the ability to shape the transverse and longitudinal density profile of the plasma source to create a controlled density ramp for emittance preservation or a plasma column with a prescribed width. One of the experimental challenges of this scheme is aligning the plasma source to the electron beam. This challenge is exacerbated with high-current electron beams, as it is difficult to accurately determine the electron beam vector at the waist using optical transition radiation-based beam diagnostics. We present a novel alignment technique developed at the Facility for Advanced Accelerator Experimental Tests II (FACET-II) designed to circumvent this difficulty. To perform the alignment, we observe the plasma afterglow light generated by the PWFA at two different longitudinal locations while scanning the transverse position of the plasma column across the electron beam. By analyzing the relative plasma light intensity as a function of the transverse position of the plasma column at the two different longitudinal locations, we determine the relative angle between the electron beam and the plasma column and correct it. In the E301 experiment at FACET-II, we aligned a 1-meter plasma source to a 10 GeV, 1.6nC electron beam to within 10um, on the order of the pointing jitter of the laser.
The Advanced WAKefield Experiment (AWAKE) relies on the self-modulation of a long proton bunch in plasma to resonantly excite wakefields. We use a relativistic ionization front to provide initial transverse wakefields for the self-modulation to grow from. It was shown that when the amplitude of the initial transverse wakefields exceeds a given value, a transition between two regimes, self-modulation instability (SMI) and seeded self-modulation (SSM), occurs. In the case of SSM the timing of the self-modulation along the bunch, and thus of the wakefields, becomes reproducible. We now show experimentally that, when transitioning from SMI to SSM, the self-modulation process also becomes more reproducible in amplitude. Amplitude reproducibility is essential for deterministic injection, and energy gain of a witness bunch.
RF breakdown limits the attainable acceleration gradient in normal conducting RF structures, challenging high-gradient operations. Recent experiments at the Argonne Wakefield Accelerator (AWA) suggest short RF pulses (a few nanoseconds) can mitigate this breakdown. We simulated dark current emission in the short-pulse regime to study breakdown initiators including field emission and multipacting. This study integrates analytical and numerical modeling of dark electron generation to understand multipacting and RF breakdown in structures driven by short RF pulses. We simulated electron trajectories under various conditions in the electromagnetic fields. Our analytical model, compared against simulations, predicted multipacting resonance modes and secondary electron yield. Our findings have revealed the dependence of dark current generation on the RF field strength, pulse duration, and surface properties. These insights guide the design of RF structures with enhanced performance and reduced breakdown susceptibility, advancing the next-generation short-pulse accelerators.
During a laser wakefield acceleration experiment, accelerated electrons produce betatron X-rays which contain information about the evolution of electron energy as they propagate through the plasma. As the electrons are accelerated, the critical energies of their synchrotron-like X-ray emission spectra change with time. In the case of a transverse density gradient, the wakefield curves towards the region of lower density. Because the electrons are continually radiating, the betatron X-rays streak across the screen of an X-ray CCD camera, converting the critical energy’s time dependence into a spatial dependence that can be directly measured with a filter pack. The pack is composed of columns of individual filters made of aluminum or copper of varying thicknesses. Each column is identical and allows us to calculate the critical energy at discrete angular positions. After background subtraction and flattening out spatial nonuniformities, the critical energy is determined by comparing the measured data through each filter in a column with a calculated signal corresponding to a spectrum with a particular critical energy until the difference between them is minimized. By repeating this process for each column, we are able to track the change in critical energy as the X-rays swept across the screen. This provides valuable insight into the electron dynamics over the course of a single shot. This method can be extended to any X-ray source with a nonuniform angular spectrum, given a known functional form of the energy spectrum.
Anthony Lu, Hailang Pan, Deepak Sapkota, Aodhan McIlvenny, Alexander Picksley, Adrian Woodley, Vassilia Zorba, Eric Esarey, Cameron Geddes, Anthony Gonsalves, Tong Zhou, Jeroen van Tilborg
Lawrence Berkeley National Laboratory, Berkeley, CA 94720
Many kilohertz repetition rate, ultrashort-pulse lasers generate Gaussian-profile beams. Nonlinear post-laser compression using near-field solids is a promising method to obtain high-power, very short laser pulses for accelerator applications, but requires homogenized flat-top profile beams to avoid spatio-temporal coupling. kHz flat-top laser beams are also used in large scale material processing. For laser plasma acceleration (LPA), reversing laser pulses from a flat-top to a Gaussian beam can improve efficiency. Thus, it is important to have high precision, high power techniques that can shape beams from kHz ultrafast lasers. PiShapers are commonly used to transform beams with high spatial coherence from Gaussian to top hat. However, their efficacy is strongly dependent on the incident beam quality and often results in obtuse edges and a less uniform transmitted beam. We show that the addition of a spatial light modulator (SLM) can improve uniformity, in our case from 47% to 94.5% across 90% of the beam area. In high energy and high power applications, deformable mirrors (DM) can be used, instead of SLMs, to facilitate high quality, high throughput beam shaping. This work shows the potential of high-precision beam shaping for high power laser system applications such as LPAs and manufacturing.
This work is supported by the U.S. Department of Energy (DOE) under Contract No. DE-AC02-05CH11231.
Multi-kHz laser plasma accelerators (LPA) have the potential for high impact applications in scientific, medical, industrial and security fields. Today’s >100MeV LPAs are limited to a few Hertz repetition rates since they are driven by Ti:Sapphire lasers that have limited power handling capability and wall-plug efficiency. To address this, we propose coherently combining short pulse fiber lasers temporally, spatially, and spectrally to achieve high energy ultrashort pulses at high repetition rates.
Multi-spectral band amplification and combining is key to achieving the tens-of-fs pulse duration requirements for current LPAs. Previously, we have demonstrated record-short 42fs spectrally combined pulses, but with single-stage amplification and small pulse stretching factor. We have recently built a three-spectral-channel, multi-stage fiber chirped pulse amplification (FCPA) laser system with a nanosecond stretched pulse duration and high gain, in which we aim to combine these spectral channels and achieve ~40fs combined and compressed pulses.
The many cascaded amplifier stages in an FCPA system requires machine protection to avoid system damage.We have designed an FPGA-based protection system that implements independent control loops at different points within the amplifier chain by rapidly sensing and stopping pulses with several different errors (amplitude, duration, timing).
This work was supported by the DOE under Contract No. DE-AC02-05CH11231, Gordon & Betty Moore Foundation under Grant ID 10631, and DARPA via the Northrop Grumman Corporation.
In reducing the Low Lagrangian to a finite system for numerical computation it is generally the case that basic physical properties such as momentum and charge conservation are lost. Using a macro-particle reduction of the charge distribution function we explore the connection between the non-canonical treatment and a fully-canonical treatment recognizing that the use of electromagnetic potentials implies a constrained Hamiltonian system even when no gauge choice is made. For the canonical system, a loss of a conservation law directly implies a loss of a continuous symmetry; we see that charge and momentum conservation rely on properties that are effected differently by the method of discretization. We present here discretization schemes which preserve the symmetries needed to conserve charge or momentum in an effort to better understand the necessary structures and determine if a useful discrete canonical system can maintain both conservation laws.
At UCLA, a plasma source using capillary discharge has been developed and studied for its potential use in plasma wakefield experiments at MITHRA and AWA facilities. This compact source, measuring 8 cm in length, can generate plasmas with a wide range of densities, making it suitable for various plasma wakefield acceleration (PWFA) experiments. With a 4-mm aperture, it can accommodate high-aspect ratio beams. This paper discusses the design and assessment of the capillary discharge plasma source, along with the use of an interferometric diagnostic system to measure plasma density.
We present experimental results from Helmholtz-Zentrum Dresden-Rossendorf of a THz Smith-Purcell Radiation source generated using Laser Wakefield Accelerator electron bunches. Affordable and small, aluminum-coated gratings were placed near accelerated electron bunches with an average energy and charge of 405 MeV and 467 pC to produce strong, coherent emission. The generated shots of radiation were transmitted through a high-pass filter, and had significant enough energy to be observable on a Pyrocam IV pyroelectric detector. Initial analysis suggest energy per shot within the 10s-100s uJ range, with peak electric fields as large as 0.66 MV/cm incident on the detector. Furthermore, the known exponential dependence of Smith-Purcell Radiation for a pencil electron beam as a function of distance from the source (grating) was modified due to the transverse size and shape of the electron bunch, and could be explained using a 1D model.
Laser-driven ion accelerators (LDIAs) generate high-intensity beams, offering immense potential across various applications, including investigating ultra-high dose rate radiobiological research. The significant beam divergence of laser-driven proton beams at the source requires capture and transport of these beams to maintain a high particle intensity at the sample site located outside the main target chamber. At the BELLA Center's iP2 beamline, we have deployed two beam transport configurations, leveraging permanent magnets for compactness, to reliably deliver up to 30 MeV protons to biological samples at high particle intensities. In conjunction with these setups, a comprehensive suite of diagnostic tools was implemented for dosimetry tasks, including multiple integrating current transformers (ICTs) for indirect online dose measurements and calibrated radiochromic films (RCFs) to measure the dose distribution and calibrate the ICTs. With the use of Monte Carlo simulations of the beamline, we achieve accurate dose estimates applied to the samples, while accounting for the linear energy transfer (LET)-dependent response of RCFs. The proton beam transport was successfully used for in vivo biological sample irradiations and is available to future users of BELLA iP2.
Work was supported by the U.S. DOE Office of Science, Offices of FES and HEP under Contract No. DE-AC02-05CH11231, and by LaserNetUS. S. Hakimi was supported by the U.S. DOE FES Postdoctoral Research Program administered by the Oak Ridge Institute for Science and Education (ORISE) under Contract No. DE-SC0014664. B. Stassel was supported by the U.S. DOE, Office of WDTS, Graduate Student Research (SCGSR) program under Contract No. DE‐SC0014664.
The AWAKE experiment at CERN explores accelerating electrons using proton-driven plasma wakefields. A crucial challenge is creating long (10-100 meters), highly uniform plasmas with electron densities in the range of 1 to 10 x 10$^{14}$ cm$^{−3}$. This presentation describes the first experimental test of a 10-meter discharge plasma source (DPS) in the AWAKE experiment.
The DPS uses a double-pulse direct-current discharge in noble gases (He, Ar, Xe) and its shot-to-shot reproducibility was investigated across a wide range of pressures (8-45 Pa) and currents (300-600 A). The plasma density was characterized using longitudinal interferometry over hundreds of shots.
The DPS’s applicability and readiness were assessed in the AWAKE experiment by propagating the 400 GeV proton bunch through the plasma and observing the development of the self-modulation instability (SMI). The measured SMI frequency corroborated the plasma density values obtained through interferometry. These results demonstrate the DPS's potential for use in AWAKE and pave the way for future studies on achieving the critical 0.25% longitudinal density uniformity needed for electron acceleration.
The development of plasma channels is of great interest for many applications, including Laser Wakefield Acceleration (LWFA). However, the creation of meter-scale plasma channels that allow precise spatial and temporal control remains a complex challenge. Designing a plasma channel involves determining an optical phase that can generate the required intensity profile at the focus. In this presentation, we explore the use of advanced computational techniques, specifically the adjoint optimization algorithm, to fine-tune the phase of a focusing optic. Known for its efficiency and accuracy, the adjoint optimization algorithm iteratively adjusts parameters to minimize a cost function. This process effectively shapes the target pulse along the axis by optimizing the curvature of a reflective mirror. To demonstrate this, we examine how the adjoint algorithm optimally reduces the focal spot size of a mirror which has a predetermined solution, i.e., a parabolic surface. We will delve into these findings in detail, highlighting the potential of adjoint optimization in optical design for creating plasma channels suitable for LWFA applications.
Generating multi-GeV electron beams with Laser-Plasma Accelerators is accessible with PW class lasers [1] but requires an accelerator many Raleigh lengths long. A plasma waveguide is often used in LWFA experiments to combat drive laser beam diffraction and increase the electron energy gain. Hydrodynamic Optically Field Ionized (HOFI) plasma channels are particularly suitable for LWFA experiments since they support density gradients that guide the drive laser and are free-standing [2-4]. These channels rely on a gas jet to form an initial gas stream, which is then ionized and shaped by a channel forming pulse to create effective plasma waveguides. Recently, a 9 GeV electron beam at BELLA PW was created using a HOFI channel generated with a 30 cm long gas jet [5]. The characterization of the gas density profile of both short (~5cm) and long (~30cm) gas jets was essential to this result. This poster will discuss the impacts of various parameters on gas jet performance, highlighting key improvements that enhance the repetition rate and optimize the gas density profiles for HOFI channel LWFA experiments.
[1] A. Gonsalves Phys. Rev. Lett. 122, 084801 (2019)
[2] A. Picksley, Phys. Rev. Accel. Beams 23, 081303 (2020)
[3] L. Feder et al., Phys. Rev. Research 2, 043173 (2020)
[4] B. Miao et al., Phys. Rev. X 12, 031038 (2022)
[5] A. Picksley, in preparation
This work was supported by the U.S. Department of Energy (DOE), Office of Science, Offices of High Energy Physics, and DARPA under Contract No. DE-AC02-05CH11231.
The generation of meter-scale, low density (≤10^17 cm^(-3)) plasma waveguides [1,2] in long supersonic gas jets has enabled the consistent production of multi-GeV electron beams in laser wakefield acceleration (LWFA), using drive pulses of just a few hundred TW [3,4,5]. The customizability of these waveguides has opened a wide parameter space for LWFA performance since the electron injection and acceleration process depends on properties of the drive pulse and waveguide structure. Our group recently developed a model of beam evolution in a plasma waveguide and its effects on enhancing and suppressing ionization injection [5]. In this poster, we present experimental results demonstrating the effects of waveguide properties on ionization injection and the characteristics of resulting electron beams from 30cm self-waveguided LWFAs. We further show that, under optimum conditions, stable production of >100 pC, multi-GeV beams can be achieved.
This work was supported by the U.S. Department of Energy (DE-SC0015516, LaserNetUS
DE-SC0019076/FWP#SCW1668, and DE-SC0011375), the National Science Foundation (PHY2010511), and the Defense Advanced Research Projects Agency (DARPA) under the Muons for Science and Security Program. E. Rockafellow is supported by a NSF Graduate Research Fellowship (DGE 1840340).
References:
[1] L. Feder et al., Phys. Rev. Res. 2, 043173 (2020).
[2] J.E. Shrock et al., Phys. Plasmas 29, 073101 (2022).
[3] B. Miao et al., Phys. Rev. X. 12, 031038 (2022).
[4] B. Miao et al., Physics Today 76(8), 54-55 (2023).
[5] J.E. Shrock et al., Phys. Rev. Lett., in press (2024).
We pay homage to previous work using multiple laser pulses shown to yield widespread benefits in laser driven particle acceleration and radiation generation - and here explore the consequences of scaling the interaction to an “infinite” number of co-propagating beamlets which couple together and form large-gradient, periodic accelerating structures capable of elevated injection for high-charge and high-energy electron acceleration. Taking advantage of fully kinetic particle-in-cell (PIC) simulations with periodic boundary conditions, we demonstrate tailoring the interspacing beamlet distance can lead to a two-order of magnitude increase in accelerated charge per pulse, an order of magnitude increase in the electron cutoff energies, prolonged pulse propagation beyond single pulse depletion, and an overall reduction in the self-injection threshold. Continual reduction of the inter-pulse spacing below a characteristic distance of a half beam waist leads to a plane-wave like acceleration dynamic which collapses the acceleration process into 1D, eliminating transverse focusing fields which may be deleterious for emittance preservation and positron acceleration. It is demonstrated this “infinite” pulse dynamic can be recovered with as few as a dozen co-propagating pulses (in 2D). Using modest laser energies, we propose this work to be a key candidate for scalable kHz, ultrashort fiber arrays for unprecedented electron luminance. Further work proves a similar principle can be extended to solid-target ion acceleration for enhanced cut-off energies, fluxes, and decreased divergence.
The APS linear accelerator produces electron beams with energies on the order of 425 MeV. Using a low emittance photocathode electron gun as a source, we will be able to test compact accelerator structures and other advanced accelerator components in the Linac Extension Area (LEA). LEA includes a 270 mm inner diameter vacuum chamber equipped with two vacuum shutters for easy installation of the device under the test during regular linac operations and experiments. In the present work, we outline proposed LEA hardware upgrades and present parameters of a proposed photocathode gun drive laser upgrade. Using corrugated waveguide accelerating structures as an example, we summarise the expected electron beam energy resolution of a bending magnet spectrometer in LEA.
Flat and magnetized beams are special beams to be used for increasing luminosity of the colliders and cooling of hardon beams, respectively. Magnetized beam generated by the photoinjector with non-zero magnetic field at the cathode can have high relativistic factor larger than 50 to be applicable for high-energy hadron beam cooling. Thus, it is hard to transport using conventional solenoid magnet. The idea of magnetized beam transport is that we remove the coupling terms of the beam by using skew triplet, enabling to transport it using normal quadrupole magnets. After the skew triplet, transverse coupling is removed, but the transverse emittance becomes associated with the original magnetization, leading to the large emittance ratio between horizontal and vertical planes. This is called flat beam. Then, using another skew triplet, flat beam can be transformed back to the round, magnetized beam for the actual application. We performed the experimental demonstration of round-to-flat and flat-to-round beam transformation at the Argonne Wakefield Accelerator (AWA) Facility. In this study, we present the experimental data analysis compared to the particle tracking simulation results. In addition, we also show the discussions on the flat-to-round beam transformations such as beam shape, FRBT condition and experimental considerations.
This study presents a Dielectric Laser Accelerator (DLA) tailored for single-electron acceleration, optimised for particle survival and minimal beam energy spread. Leveraging a genetic algorithm, we strategically design the dielectric structure to achieve efficiency in both computational runtime and structure performance.
The study focuses on three key aspects: the selection of a suitable electron source with the right emittance, beam dynamics for sub-relativistic and relativistic electrons, and the alignment of beam properties with the requirements for indirect dark matter search. Our findings establish DLA as a promising tool for advancing dark matter research.
Indirect dark matter exploration necessitates a high repetition rate of single electrons in the GeV energy range. The DLA's potential to operate at GHz rates makes it an ideal candidate for designing a compact accelerator for dark matter search. To achieve high repetition rates, a suitable laser and electron source are essential. Hence, we introduce RF-based electron microscope type-sources for our design, as they can operate at 3GHz or higher.
A segmented optimization approach is employed to the structure accelerating particles from 10 MeV to 1GeV. Instead of conducting global optimization for the entire DLA structure length, we will employ a localized optimization strategy, optimizing each 10mm-long segment independently while iteratively adjusting the input beam conditions for subsequent segments. Through this iterative process, the DLA structure can be optimized in an efficient runtime. The output beam parameters like energy spread and survival rate will be compared to the parameters required for indirect search of dark matter.
Over the past decade, the development of compact and cost-effective laser plasma accelerators (LPAs) operating at kHz repletion rates has opened attractive possibilities for practical applications, such as ultrafast electron probing and photon sources. In addition to high-flux, the high repetition rate enables active feedback stabilization in these accelerators, as mechanical instabilities fall below 200 Hz. This capability can ensure beam quality and repeatability, enhancing the overall performance and reliability of LPAs. Monoenergetic MeV-range electrons with pC charge can be generated in the resonant blowout regime using compact kHz lasers with few mJ energies and post-compressed to few-cycles durations [1]. Moreover, the performance of kHz LPAs critically depends on the plasma density profile, necessitating precisely engineered gas targets below the millimetric scale operating at high gas densities (>$10^{19}$cm$^{-3}$). This work reports the fabrication of submillimetric de Laval nozzles by ultrafast laser micromachining in dielectric a ceramic to produce supersonic gas jets [2]. Nozzles were manufactured in a homemade trepanning setup, and their geometry and surface quality were studied in relation to laser and machining parameters, resulting in optimized fabrication protocols. Interferometric diagnostics confirmed that the laser machined nozzles can produce optimal gaseous targets for laser electron acceleration.
[1] J. Faure et al., Plasma Phys. Control. Fusion, 61, 014012 (2019)
[2] A. V. F. Zuffi et al., proceedings 2022 SBFoton IOPC (2022)
Funding Acknowledgements: São Paulo Research Foundation (FAPESP) (17/50332-0, 21/13737-8); National Council for Scientific and Technological Development (CNPq) (465763/2014-6, 405143/2021-4, 142246/2018-2).
Laser wakefield accelerators (LWFAs) have been successful in experimentally producing sustained gradients of tens of GeV/m over tens of centimeters. While the strength of these fields has been demonstrated, a direct measurement of the field configurations inside an LWFA especially at low densities is a huge challenge. Here, we report on the results of transverse electron beam probing of the fields inside an LWFA at densities of $10^{15} — 10^{17} cm^{-3}$, corresponding to plasma wavelengths in the range of several hundred microns. The LWFA is driven by BNL Accelerator Test Facility’s unique long-wave-infrared CO2 laser (9.2 μm) pulse, which currently generates 2 ps long pulses at 2-3 TW. The linac-produced electron beam has an energy of 50-60 MeV and about a 200 fs long bunch length. A YAG:Ce scintillator placed on a translation stage records the electron beam density profile at distances of up to 10 cm from the plasma. Particle-In-Cell Simulations using OSIRIS are used to corroborate the results of the experiment.
Laser wakefield accelerator-driven betatron x-rays are bright, broadband synchrotron-like emission with micrometer-scale source size and sub-picosecond duration. Betatron x-rays provide a new avenue for high-resolution, high-throughput imaging of additively manufactured (AM) materials. AM alloys are commonly used in aerospace and automotive industries due to high strength and stiffness to weight ratios. Using the Advanced Laser Light Source betatron beamline in Qc, Canada, we performed high-resolution 3D tomography of AM aluminum-silicon-magnesium (AlSi10Mg) alloys under tensile load. Prior to x-ray tomography, the betatron source was optimized from a He-N2 gas jet for x-ray imaging at 2.5 Hz. X-ray tomography of pores in AlSi10Mg samples over 180° with 3° increments at 2.5 Hz were obtained in 72 minutes. This rate of tomography enabled visualization of micrometer pore dynamics under different tensile loads prior to fracture. To improve the data acquisition rate, we require enhancement of betatron flux and source stability. Accordingly, we have further optimized the betatron source using a 7 mm 3D printed gas cell, leading to ~ 6x higher flux and ~ 20x reduced pointing fluctuation compared to the gas jet targets. We estimate that using gas cell targets, we could perform 180° tomography at 3° increments in approximately 15 minutes. Upcoming experiments will strengthen our original studies by providing additional porosity evolution data to validate degradation models and thereby, advancing our understanding of ductile fractures in AM alloys.
Plasma-based acceleration (PBA) has emerged as a promising candidate for the accelerator technology used to build a future linear collider and/or an advanced light source. In PBA, the witness beam needs to be matched to the focusing forces of the wakefield (WF) to reduce the emittance growth. In some linear collider designs, the matched spot size of the witness beam can be 2 to 3 orders of magnitude smaller than the spot size (and wavelength) of the WF. Such an additional disparity in length scales is ideal for mesh refinement where the WF within the witness beam is described on a finer mesh than the rest of the WF. We describe a mesh refinement scheme that has been implemented into the 3D QS PIC code, QuickPIC. A fast multigrid Poisson solver has been implemented for the field solve on the refined meshes and a Fast Fourier Transform (FFT) based Poisson solver is used for the coarse mesh. A series of intermediate meshes are used to improve accuracy. The code has been parallelized with both MPI and OpenMP, and the parallel scalability has also been improved by using pipelining. An adaptive mesh refinement technique is implemented to optimize the computational time for simulations with an evolving witness beam size. Several test problems are used to verify that the mesh refinement algorithm provides accurate results. The results are also compared to highly resolved simulations with near azimuthal symmetry using a new hybrid QS PIC code QPAD.
The Hundred Terawatt Thomson (HTT) laser system at the LBNL BELLA Center operates a laser-plasma accelerator to produce high energy (~100s MeV) electron beams. A second high-intensity laser beam is scattered off of these electrons, boosting the photon energies from the eV to MeV range, in order to produce a tunable source of gamma rays for applications in security and the probing of high-Z or high-density materials [1, 2]. This requires a stable beam of electrons in terms of pointing and position, which in turn necessitates that the laser beam driving the acceleration process is also stable. This presentation will give details on the work towards improving the position and pointing stability of the laser beam driving the electrons, which makes use of commercially available equipment, and builds on previous projects at the LBNL BELLA Center [3, 4]. An overview of the implementation of the system will be presented, and the improvement to the LPA-produced electron beams will be shown in terms of the stability of the spectrum, beam divergence, and beam pointing.
This work was supported by the U.S. Department of Energy (DOE) Office of Science, under Contract No. DE-AC02-05CH11231.
[1] C. Geddes et al., Impact of monoenergetic photon sources on nonproliferation applications final report, Technical Report, 2017
[2] C. Thornton et al., arXiv:2404.09270v1, 2024
[3] F. Isono et al., High Power Laser Science and Engineering, 9, e25, 2021
[4] C. Berger et al., Physical Review Accelerators and Beams, 26, 032801, 2023
Laser plasma accelerators (LPAs) have emerged as a promising alternative to classical accelerators for a variety of applications, due to their ability to produce high brightness beams and significantly higher accelerating gradients, allowing more compact designs for future light sources and colliders. However, the LPA mechanism comes with a unique set of challenges based on the nature of the interaction between the laser pulse and the plasma. In order to enable reliable operation of an LPA driven FEL, key parameters that drive the LPA interaction need to be closely monitored and controlled. A critical parameter for this interaction is the spectral phase, which determines the chirp and pulse length of the driving laser. We report on a diagnostic implemented in our experimental setup that allows full on-shot characterization of the spectral phase and amplitude of the amplified laser. This enables detailed investigations of the correlation between the spectral phase and LPA, as potentially the FEL performance.
Structured solid-density or foam Ion Source Targets (ISTs) driven by PW-class lasers can generate ion beams with desirable characteristics via Hole-Boring Radiation Pressure Acceleration (HB-RPA) mechanism. Since HB-RPA accelerates ions perpendicular to the front surface of the IST, judicious target front surface fabrication translates to engineered velocity distribution. Ion beams with exotic and useful phase-space distribution, such as a convergent ion flow leading to extremely high energy flux at a well-defined focal length, can be generated. These beams have broad applications including nuclear fusion, cancer therapy, warm dense matter generation, among others. In particular, the IST-generated low-emittance monoenergetic ion beam provides an efficient way to generate an ignition spark for a pre-assembled massive nuclear fusion, leading to higher-gain fusion energy. We discuss the limiting factors for the IST acceleration and beam quality preservation including laser profile, polarization, and target density. Specifically, the temperature of the electrons nearly neutralizing the ion beam poses a limiting factor on beam emittance and spectra. Using additional structures placed at the beam path, the electron population coupled with ion beam can be modified, providing a way to improve the ion beam quality.
The high accelerating gradients of plasma-based acceleration can lead to beams with large projected energy spread, which necessitates schemes for energy spread reduction. Here we present a ‘direct beam-loading’ scheme that uses the Trojan Horse injection method [1] to produce ultrahigh brightness beams in a single stage with a single bunch. Witness charge is optimised in simulation for projected energy spread minimisation to achieve 6D brightness of order $10^{17}\mathrm{A/m}^2 \mathrm{rad}^2/0.1\% \Delta E/E$ and slice brightness an order of magnitude above this. The relative energy spread is robust against witness charge variation, and combined with resilience to spatiotemporal jitter provided by the long plasma wavelength [2] ultrahigh brightness is maintained. Relative projected energy spread is locked in after ~20 mm of acceleration which provides scope to maintain beam properties to multi GeV energies.
Beam-driven plasma wakefield acceleration can sustain accelerating fields on the GV/m scale, making it well-suited for linear collider applications. However, in recent years, an efficiency-instability relation has been proposed, which limits the energy transfer efficiency from the wake to the trailing bunch that can be achieved without inducing transverse instabilities detrimental to the transverse phase space of the accelerated bunch. We discuss the efficiency-instability relation for a transversely misaligned trailing bunch and a novel method that can be used to identify the beam-breakup instability (BBU) on a dispersive dipole spectrometer and quantify the size of the instability. We show preliminary results using data from the E300 experiment at the FACET-II facility, showcasing the use of this method.
It is well known that high (105 to over 1010) temporal laser pulse contrasts are necessary to mitigate undesirable prepulse effects in laser-plasma acceleration (LPA) and other high-field applications. Many pulse contrast enhancement schemes have been devised to meet this requirement, but tend to suffer from low efficiency, inadequate prepulse suppression, beam distortion, or a combination thereof. Furthermore, developing a design that may tolerate Joule-class energies at high repetition rates (multi-kW average powers) as envisioned for the next-generation LPA drivers has been a challenge.
We present a compact multi-pass cell (MPC) pulse cleaning scheme that is scalable to high repetition rates and multi-Joule energies while maintaining beam quality, designed for the flat-top nanosecond pulses of a coherently combined fiber laser system after temporal combining but before compression. This approach leverages nonlinear effects to strongly attenuate low-power prepulses while transmitting the high-power main pulse with low loss. Considering only cleaning losses, simulation indicates that for 1.8 J pulses a 2.52m cavity may provide 100 dB (1010) of prepulse suppression at 90% main pulse power transmission and negligibly low (< 0.8π radians) B-Integral. In the near term, we are pursuing an experimental demonstration with low energies as a proof of concept. Simulation of this design with 10 mJ pulses indicates that a cm-scale cavity can provide over 60 dB (106) of prepulse suppression at 91% main pulse transmission and low B-Integral (< π radians). Experimental validation of this result is in progress.
At AWAKE, self-modulation of a long relativistic proton bunch is used to drive high-amplitude wakefields. As the proton bunch self-modulates while propagating through the 10 m long plasma, the amplitude of the wakefields grows. Measuring the wakefield amplitude directly has not been possible so far. However, as the energy stored in the wakefields is dissipated, some fraction of it is emitted as light. By measuring the intensity of the light, we observe for the first time the growth of the self-modulation process along the plasma. By varying bunch and plasma parameters, we investigate the dependencies of the self-modulation growth. When imposing a density gradient along the plasma, we also observe growth suppression, as predicted by theory.
Plasma-based particle accelerators maintain accelerating fields that are several orders of magnitude higher than conventional accelerators. This allows for more compact accelerator footprints that can deliver particle beams of very high charge (> 100 pC) and large current (> kA) for various applications. For instance, plasma-wakefield accelerators are promising candidates for next-generation TeV-class electron-positron colliders for high-energy physics and secondary light sources. However, to reach the desired TeV energy regime, a staging approach of independent laser-driven plasma accelerators that each preserve low energy spread and beam emittance is required. Maintaining beam emittance over tens and hundreds of stages is a serious challenge but is crucial to achieving a high luminosity in future colliders. We present results for the optimization of plasma-stage downramp profiles and inter-stage beam transport in simulations of multi-stage plasma accelerators, carried out with codes from the Beam pLasma & Accelerator Simulation Toolkit (BLAST) and steered by optimas, a Python library for optimization at scale, powered by libEnsemble.
Supported by the CAMPA collaboration, a project of the U.S. Department of Energy, Office of Science, ASCR and HEP, SciDAC program, and Exascale Computing Project. See comments for full details.
Plasma being a non-linear medium leads to a whole range of phenomena, like Stimulated Raman Scattering (SRS), Stimulated Brillouin Scattering (SBS), cross-talk between laser beams, cross-energy beam transfer (CBET), among others. These effects are important in the frame of both indirect-drive Inertial Confinement Fusion (ICF) and direct-drive ICF. Consequently, achieving a balanced laser energy deposition in ICF on the target relies on a meticulous assessment of CBET-related effects.
Various strategies for avoiding CBET have been proposed, including beam diameter reduction, wavelength detuning, and laser bandwidth increase. However, most of these investigations have been confined to unmagnetized plasma. Recently, the first measurements of CBET saturation by ion heating at OMEGA have identified the sensitivity of CBET to ion temperature. These measurements suggest that CBET can be effectively reduced when the local plasma temperature is enhanced. According to our former experiments, this enhancement can be achieved simply by using an external magnetic field.
Our study comprehensively explores the influence of external magnetization on cross Talk (CT) and laser-plasma interactions in the context of inertial confinement fusion (ICF) experiments. Our findings, amalgamating experimental measurements and analytical equations, offer promising prospects for enhancing inertial confinement fusion yields. This study establishes the theoretical and experimental groundwork necessary for understanding and optimizing laser-plasma interaction in magnetized conditions, paving the way for significant advancements in the field of ICF.
We investigate the production and subsequent confinement of an electron-positron pair plasma when a laser pulse of ultra-relativistic intensity collides with a beam of incoherent gamma-rays. The secondary fermions tend to be confined when the radial ponderomotive force due to the laser intensity profile is balanced by the radiation damping (recoil) that they experience due to energetic photon emission. The particle-in-cell calculations are based on experimental conditions that may be realizable with a petawatt-class argon fluoride laser.
The next-generation precision laser-plasma accelerators (LPA) require kHz repetition-rates and higher to enable feedback control, and to meet application rep-rate needs. Coherently combined fiber lasers, efficient and high-power, are considered one of the most promising laser technologies to drive kHz LPAs. Since LPAs need short laser pulse durations at tens-of-fs, the pulse stretcher, compressor, and pulse shaping in a fiber chirped-pulse amplification (FCPA) system need to be broadband, and the broad bandwidth needs to be maintained with high gain (~100dB).
We have designed and implemented novel short-pulse methods in a high-energy FCPA system, including specialty fiber based pulse stretching, programmable pulse shaping, distributed spectral filtering, and out-of-plane Littrow configuration grating compression. We have developed a FCPA system dispersion model and matched dispersion of different orders. Dispersive fiber based pulse stretcher has been fabricated and is broadband, polarization-maintaining, and compact. A pulse shaper is programmed with the capability to independently tune different orders of dispersion. Multiple spectral filters are distributed in the multi-stage FCPA system to optimally compensate for strong gain narrowing and saturation. An out-of-plane Littrow-configuration grating compressor is designed to accommodate broad bandwidth and high power with high throughput. This work shows a path to achieve tens-of-fs, high-average-power kHz pulses from FCPA systems for driving LPAs.
This work is supported by the U.S. Department of Energy (DOE) under Contract No. DE-AC02-05CH11231, and Gordon & Betty Moore Foundation under Grant No. 10631
We explore the possibility of using a CO2-laser driven, self-guided wakefield accelerator as a stage for the acceleration of externally injected electron beams.
Optimal conditions for acceleration were explored through 2d and quasi-3D PIC simulations with FBPIC and WarpX. Parameters and regimes are specified by linear accelerator and CO2 laser at ATF facility in Brookhaven National Lab (BNL) [1]. Comparison studies are conducted between 800nm and 9200nm with same externally injected Gaussian beams. Multiple regimes have been explored, including : matched-laser-spot blown-out regimes (with no self-injection), quasi-nonlinear regime (1<a0<4) with matched-electron beam, and possible “re-phasing” scheme.
We look at the emittance, energy spread and divergence to determine the optimal external injection scheme. Injection misalignments between beam and laser are also considered for a robust external-injection system. Lastly, we started a machine learning initiative to guide future external-injection experiments.
[1] Zgadzaj, R., Welch, J., Cao, Y. et al. Plasma electron acceleration driven by a long-wave-infrared laser. Nat Commun 15, 4037 (2024).https://doi.org/10.1038/s41467-024-48413-y
The ERC project SPARTA (Staging of Plasma Accelerators for Realizing Timely Applications) [1] started in 2024 at the University of Oslo. With the ultimate goal of reaching electron energies beyond what is available in a single plasma-accelerator stage, it aims to solve two key challenges of plasma accelerators: beam-quality preservation between accelerating stages and stability. The project relies on two novel ideas: a new design for a non-linear plasma lens for achromatic beam transport; and a self-correction mechanism that stabilizes the acceleration from stage to stage without external control. Combining these solutions, blueprints for a multistage demonstrator facility will be proposed.
[1] European Commission: “Staging of Plasma Accelerators for Realizing Timely Applications”, https://doi.org/10.3030/101116161
A Dielectric Disk Accelerator (DDA) is a metallic accelerating structure loaded with dielectric disks to increase coupling between cells, thus high group velocity, while still maintaining a high shunt impedance. This is crucial for achieving high efficiency high gradient acceleration in the short rf pulse acceleration regime. Recent research of these structures has produced traveling wave structures that are powered by very short (~9 ns), very high power (400 MW) RF pulses using two beam acceleration at the Argonne Wakefield Accelerator Complex. In testing, these structures have withstood more than 320 MW of power and produced accelerating gradients of over 100 MV/m. A new standing wave DDA structure is being fabricated for testing on the Nextef2 test stand at KEK that will be tested on a more conventional, klystron power source. Simulation results of this structure show that at 50 MW of input power, the DDA produces a 457 MV/m gradient. It also has a large shunt impedance of 160 MΩ/m and an r/Q of 21.6 kΩ/m. Cold testing of this structure will be conducted July 2024 with high power testing beginning in August.
This paper presents the final physics design of the THz wakefield acceleration experiment using three dielectric structure cross-sections at the Argonne Wakefield Accelerator (AWA) facility. The experiment will focus on multi-bunch excitation of wakefields, exploration of the wakefield transverse-force topology, and possibly support an experiment on energy recovery. This contribution discusses start-to-end simulations of the experiment and expected experimental signature. We specifically address the resolution requirements on the beam diagnostics and the design of a THz-radiation collection system.
We are utilizing a sub-ps, sub-10 micron X-ray source for X-ray phase contrast imaging (XPCI) tomography of Inertial Confinement Fusion (ICF) fuel capsules). We will present results from an experiment in April 2024 at the Advanced Laser Light Source in Montreal, Canada. Radiography data was captured with Laser Wakefield Acceleration blowout regime betatron X-rays with a critical energy of 15-25 KeV. Experimental goals met include imaging 360 degrees of an ICF fuel capsule, and benchmarking optimal resolution parameters of the system. Imaging the full rotation of the object will allow us to do a tomographic reconstruction of these fuel capsules with a resolution of ~4 um. The optimal resolution benchmarked is ~1um, which is comparable to current methods. We use X-ray phase contrast imaging to differentiate between thin low Z layers in the ICF fuel capsule. The Fresnel-Kirchoff integral formula can be used to determine source characteristics from XPCI fringes seen in radiographs1, we will also employ HADES (an X-ray ray tracing simulation code). The results of this experiment provide a comparison of current industrial methods such as X-ray tubes to LWFA based X-ray sources. Ultimately, our aim is to develop a diagnostic for not just target metrology of ICF fuel capsules, but employable to observe ICF implosions with unprecedented spatio-temporal resolution.
This work was performed under the auspices of the Lawrence Livermore National Security, LLC, (LLNS) under Contract No. DE-AC52-07NA27344.
References
[1]Vargas, X-ray phase contrast imaging of additive manufactured structures using a laser wakefield accelerator. PPCF, 61 (2019) 054009.
Because of their ability to produce high gradients, radiofrequency (RF) structures in the sub-terahertz (sub-THz) regime are of considerable interest in structure wakefield acceleration. These structures can be used to generate a high gradient and high efficiency wakefield, allowing for a low physical footprint. In the pursuit of a structure with these properties, we have designed and built a metallic corrugated W-band structure based on the available electron beams at the Argonne Wakefield Accelerator (AWA) with the emittance exchange (EEX) beamline. The EEX beamline offers the possibility to perform longitudinal bunch shaping to optimize the gradient and the transformer ratio (defined as the accelerating gradient at the witness bunch over the decelerating gradient at the drive bunch in the two-beam acceleration regime). This talk will present the testing results of the W-band structure when excited by 42 MeV bunches sent through the EEX beamline. Two cases were studied: (1) demonstration of a high gradient from a single drive electron bunch with a charge of 10 nC and a short bunch length of about 150 microns; (2) demonstration of a high transformer ratio using a two-bunch train, where the drive bunch with about 2 nC of charge was shaped with a transverse mask, and a small witness bunch trailed behind to measure the wakefield. Detailed results will be presented in this talk, showcasing the promise of sub-THz wakefield acceleration with longitudinal bunch shaping.
QuickPIC is a parallel 3D PIC code that applies the quasi-static approximation. QuickPIC can simulate both beam driven and laser driven plasma wake field accelerators with a speed that is 1000 times faster than the conventional PIC code without losing accuracy. QuickPIC is developed based on the frame work UPIC, which has a hybrid parallelism algorithm that uses both OpenMP and MPI. Such an algorithm is also suitable for a GPU cluster. In this work, we will introduce the GPU+MPI version of QuickPIC, including the algorithm for deposit, particle mover and sine and cosine FFTs. The comparison of computing time between GPU and CPU versions of QuickPIC is also presented.
Laser plasma accelerators (LPAs) have promise to be the next generation accelerator for colliders, as well as drive a number of basic science, industry, security and medical applications. Many applications require high brightness electron beams enabled by low emittance. One proposal to achieve ultra-low emittance from an LPA is a two color laser configuration, where a long wavelength laser, with large ponderomotive force, is used to excite a plasma wakefield, while another trailing short wavelength laser is used to ionize inner shell electrons, injecting them in the accelerating phase of the wake [1]. The short wavelength allows for a high electric field for ionization, with low ponderomotive force. Many LPAs use Ti:Sapphire based lasers with central wavelength 0.8 μm. We will present experimental results and simulations performed at the BELLA Center on generating the third harmonic of short (45 fs), high fluence (30 mJ/cm2), Ti:Sapphire based laser pulses for the purpose of ionization injection in a quasi-linear wake. Features and challenges unique to short pulse, high fluence harmonic generation and characterization as well as how those challenges were addressed will also be presented.
[1] L.L. Yu, Two-Color Laser-Ionization Injection, PRL 112, 125001 (2014)
This work was supported by the U.S. Department of Energy (DOE), Office of Science, Offices of High Energy Physics, under Contract No. DE-AC02-05CH11231and by the National Science Foundation (NSF) under grant DGE 1752814.
The Argonne Wakefield Accelerator (AWA) supports research on advanced acceleration, beam manipulation, and beam production with the goal of enabling the next generation of accelerators for the energy frontier. Additionally, this research is synergistic with R&D on compact X-ray light sources. We discuss near-term upgrade plans to improve beam brightness and stability. Furthermore, we describe longer-term upgrades aimed at increasing beam energy to enable next-generation beam-driven wakefield accelerators. These upgrades include generating bright 500-MeV electron bunches using the two-beam accelerator concept and potentially doubling the beam energy of the AWA facility through collinear-wakefield acceleration.
Cesium antimonide photocathodes are well-known for their high performance as electron sources for various accelerator methods such as X-ray Free Electron Lasers (XFEL), ultrafast electron diffraction, particle colliders, and more. While the crystals Cs3Sb and Cs1Sb are distinguishable, the crystalline and optical properties that determine the Quantum Efficiency (QE) and Mean Transverse Energy (MTE) are not well-understood. Scattering mechanism in these photocathodes may explain the unexpected loss in energy of emitted electrons, which severely restrict photocathode performance, and require a deeper understanding to achieve a quality that will enhance applications within the field. The goal of this project is to combine Density Functional Theory (DFT) with Monte Carlo simulations to study the effect of stoichiometry and energy loss of the cesium antimonide thin-film photocathodes. DFT is used to generate bandstructures of the crystals and obtain useful parameters that define the crystal such as bandgap energies between different valleys, effective masses, sound velocities in the crystal, density, etc. These parameters can then be input into the Monte Carlo simulation to calculate the energy of individual electrons as they excite, scatter, and eventually emit from the crystal, allowing for study of the scattering mechanisms and their effect on the emission energy distribution. This will eventually lead to the optimization of these photocathodes.
UT3 Accelerator Applications Development Facility
P. Franke 1,2, E. W. McCary 1,2, T. Ha 1,2, D. Phan2, T. Borger1, J. Brooks2, J. F. Altamirano2, C. Hojbota2, H. L. Smith1,2, R. van Mourik1, G. R. Plateau1, O. Z. Labun2, L. Labun1,2, R. Kumar1, M. Gracia1, S. Dale1, M. Connolly1, M. C. Downer2, S. V. Milton1 and B. M. Hegelich1,2
1Tau Systems Inc.
2U. Texas at Austin
[email protected]
Tau Systems Inc. is developing laser-driven particle accelerators for industrial, medical and research applications. In partnership with the University of Texas at Austin, Tau has upgraded the existing 30TW UT3 laser system and completed initial commissioning of an applications-focused laser wakefield accelerator (LWFA) beamline. This poster reviews laser and electron beam performance parameters, and current and future LWFA and applications development projects. Projects advancing accelerator performance include developing gas-targets/injection techniques, accelerator control/data acquisition/feedback systems and diagnostics/analysis techniques all at rep-rate. Current and future applications-focused projects include space-bound electronics testing, medical imaging and radiotherapy, and semiconductor-relevant X-ray metrology.
Keywords: Laser wakefield acceleration, Electron sources, X-ray imaging, High intensity laser-plasma interactions, Accelerator applications, Laser applications
Dielectric Laser Accelerators (DLAs) have been shown to produce GeV/m acceleration gradients and therefore the potential to shrink commercial accelerators to the cm scale. However, increasing energy gain requires multi-mm interaction lengths, which has previously been limited by dephasing. Progress in optical techniques has made controlling the phase in optical pulses common and available in scientific laboratories. Here we show that applying a liquid-crystal-mask in combination with a pulse front tilt enables the implementation of coherent control on a simple dual grating laser accelerator. Such nearly limitless live-tuning capability for the accelerator enable software-based correction of structure and optical system imperfections, implementation of transverse focusing schemes, control of the output electron beam energy and number of particles accelerated, ultimately maximizing the interaction length for up to 0.5 MeV energy gain.
Laser-plasma accelerators (LPAs) have great potential to be compact and economic, and can enable many applications in science, industry, and medicine, from wakefield colliders (e.g. 10TeV) and precision LPA facilities (e.g. kBELLA) to photon and particle sources. These applications need new kHz rep-rate laser driver technologies producing Joules of pulse energy, up to 100’s kW average power, and tens-of-percent wall-plug efficiency.
We developed a novel, energy/power scalable laser driver approach based on multidimensional coherent combining of ultrashort pulses from fiber lasers. Fiber lasers are the most efficient high power laser technology to date. Spatial beam combining enables average power and pulse energy scaling, and temporal pulse combining (stacking many amplified pulses into a single pulse) reduces fiber amplifier arrays needed for high energy to a practical size.
We have demonstrated close-to-full energy extraction (~10mJ) from 85µm-core Yb-doped fiber amplifiers and temporal combining of 81 amplified pulses. 4-channel spatial-temporal combining has achieved ~30mJ pulses at kHz rep-rates. We have shown diffractive combining of 2-D ultrashort-pulse beam arrays, and robust control of combining 81 beams. We also demonstrated record-short pulses (42fs) from fiber combination systems using spectral combining. Ongoing efforts are developing integrated fiber amplifier modules, and building scaled-up fiber systems (100-200mJ, 30-100fs, 1kW). Past and ongoing development has established a path to meet the needs of precision LPAs like kBELLA, their applications, and future colliders.
This work is a collaboration between LBNL, University of Michigan, LLNL, Optical Engines, nLight, and is supported by DOE Office of Science, DARPA, Moore Foundation.
For the last few decades, the development of Laser-Plasma Accelerators (LPAs) has attracted high interest due to the capacity of plasma to produce and sustain extremely high electric fields. The accelerating gradients in plasma accelerators can exceed 100 GV/m, which is three orders of magnitude larger than those obtained in metallic-cavity accelerators. This promisingly offers very compact alternatives to conventional linear machines . However, a high field is not the only ingredient required for achieving high multi-GeV energy gains. The accelerated beam must also follow this field over long distances. Currently, the identified main challenges for LPAs include the diffraction and depletion of the driver laser, as well as the dephasing of the accelerated beam with the driven plasma waves. Diffraction and pump depletion cause the laser intensity to decrease during acceleration, eventually suppressing the wakefield. Dephasing results from the mismatch between the phase velocity of the accelerating field and that of the electron beam, leading the electron beam toward a decelerating phase of the wake.
In this context, we discuss two approaches for overcoming these limitations and increasing the beam energy. First, we present the experimental demonstration of quasi-monoenergetic electron beam acceleration at the GeV level in a plasma waveguide created by a quasi-Bessel beam shaped by an axiparabola mirror. Another concept involves advanced optical shaping of the laser driver, allowing diffraction-free propagation over a long distance while controlling the group velocity of the laser. This approach significantly extends the effective dephasing length.
Inverse Compton scattering by relativistic electrons off intense laser pulses provides an attractive option for compact radiation sources in the (soft) X-ray spectral range. Tunability of the radiation wavelength is greatly increased by varying the crossing angle in the interaction. On the other hand, the radiated power from these sources is typically rather low, limiting the range of applications. By imposing a spatial modulation on the electron beam the Compton yield can be enhanced by many orders of magnitude via superradiant emission even when considering limiting contributions by realistic spot sizes, energy spread and beam emittance. However, attaining the required density modulation at the relevant electron beam energy is still a major challenge. We will discuss our experimental efforts on two alternative methods of achieving the required density modulation for superradiant Compton scattering at the UCLA Pegasus laboratory: ponderomotive bunching by two lasers at different frequencies and attosecond velocity bunching using an s-band buncher linac in conjunction with a x-band linearizer. Our plans to observe the coherent enhancement of Compton scattering in the near future are considered
Plasma-wakefield accelerators use tabletop equipment to produce relativistic femtosecond electron bunches. Optical and x-ray diagnostics have established that their charge concentrates within a micron-sized volume, but its sub-micron internal distribution, which critically influences gain in free-electron lasers or particle yield in colliders, has proven elusive to characterize. Here, by simultaneously imaging different wavelengths of coherent optical transition radiation (COTR) that a laser-wakefield-accelerated e-bunch generated when exiting a metal foil, we reveal the structure of the coherently-radiating component of bunch charge. Key features of the images are shown to correlate uniquely with how plasma electrons injected into the wake by either a plasma-density discontinuity, by ionizing high-Z gas-target dopants, or by uncontrolled laser-plasma dynamics. With additional input from electron spectra, spatially-averaged COTR spectra, and particle-in-cell simulations, we reconstruct coherent 3D charge structures. The results demonstrate essential metrology for next-generation compact X-ray free-electron lasers driven by plasma-based accelerators.
Precision shaping of the phase space of beams is essential for advanced acceleration methods, such as enhancement of the transformer ratio in beam driven wakefield concepts. We have experimentally demonstrated a method to generate arbitrary bunch profiles, with high precision, in a rapid, "on-demand" manner. The approach is based on a multileaf collimator (MLC) with independently actuated tungsten strips which selectively scatter unwanted particles to create high-fidelity transverse beam distributions. In conjunction with an emittance exchange beamline (EEX) at the Argonne Wakefield Accelerator, the MLC-generated transverse profiles are transformed into longitudinal bunch profiles that are highly variable, including ramped profiles with adjustable features. Enabled by novel features such as magnetically coupled actuation without lubricants, this MLC operates in ultrahigh vacuum environments. Engineering improvements of the MLC, based on a stack of shaped rotors, will also be introduced, in addition to an algorithm for mask setting. The many degrees of freedom of the MLC enable the optimization of experimental figures of merit using feed-forward control and advanced machine learning techniques.
AWAKE is a proton-driven plasma wakefield acceleration experiment at CERN. Proton drivers provided by the CERN accelerators carry a large amount of energy per bunch (~20kJ) and per particle (~400 GeV), sufficient to excite GV/m fields over tens to hundreds of meters in a single plasma. Drivers are initially much longer than the plasma wavelength and must be self-modulated to resonantly excite high amplitude wakefields.
In this contribution, we present an overview of recent AWAKE experimental results on: the observation of motion of ions and the filamentation instability using a 10m-long discharge plasma source; the demonstration of wakefield reproducibility when self-modulation is seeded; the suppression of self-modulation with a linear plasma density gradient as well as results of the effect of a plasma density step in the self-modulation plasma. Further, we describe AWAKE’s plan towards application of this acceleration scheme to particle physics.
FACET-II is a national user facility that offers a unique capability for developing advanced acceleration and coherent radiation generation techniques using high-energy electron beams. In this talk, we will present the latest results from plasma wakefield acceleration (PWFA) experiments at FACET-II, focusing on the following topics. First, we provide evidence of energy depletion of the 10 GeV drive beam and efficient energy transfer from the beam to the wake, in both beam-ionized and laser-preionized plasmas, which is a crucial stepping stone towards achieving high energy transfer efficiency from the drive to the witness bunch in the ultimate two-bunch PWFA configuration. We will also show examples of machine-learning-enabled beam tuning to increase drive beam density, thereby enhancing energy transfer efficiency. Next, we present results on generating high-energy, low-emittance beams via downramp and ionization trapping in PWFA. Using density downramp injection, we achieve the generation of electron bunches exceeding 20 GeV with small energy spread and emittance. Additionally, we show the generation of multi-GeV, multi-color electron beams via ionization injection, resulting from periodic injection induced by betatron oscillations of the drive bunch. Finally, we will discuss the first experimental attempts at beam matching to a lithium density upramp and share preliminary results from the two-bunch PWFA experiment.
Acknowledgement: The FACET-II Facility at SLAC National Accelerator Laboratory and the work at UCLA has been funded by the U.S. DoE Office of HEP.
The space-charge field of a relativistic bunch is screened in plasma due to the presence of mobile charge carriers. We experimentally investigate such screening by measuring the effect of dielectric wakefields driven by an electron bunch in an uncoated dielectric capillary where the plasma is confined [1]. We show that the plasma screens the space-charge field and therefore suppresses the dielectric wakefields when the distance between the bunch and the dielectric surface is much larger than the plasma skin depth. We also present recent experimental results from SPARC_LAB on guiding of electron bunches in a curved plasma-discharge capillary [2], and on focusing and acceleration in an all-plasma compact device [3]. We discuss the impact of these results on the design of EuPRAXIA@SPARC_LAB, a user-oriented free-electron laser based on plasma wakefield acceleration.
[1] L. Verra et al., submitted (2024)
[2] R. Pompili et al., accepted in Phys. Rev. Lett. (2024)
[3] R. Pompili et al., Phys. Rev. E 109, 055202 (2024)
Beam test facilities have been an integral part of accelerator science research, education, and applications development. However, awareness of their capabilities is limited, and potential new researchers typically face a multitude of barriers in accessing their capabilities, such as a lack of centralized information on facility capabilities or how to engage with them. BeamNetUS is a network of facilities that aims to directly address these problems through improving awareness and access to these unique facilities. For its pilot campaign, the network includes facilities at Argonne National Laboratory, Brookhaven National Laboratory, Fermi National Accelerator Laboratory, Lawrence Berkeley National Laboratory, SLAC National Accelerator Laboratory, and Thomas Jefferson National Accelerator Facility. These facilities provide complementary capabilities enabling research in plasma physics, beam physics, material science, radiofrequency sources and structures, nuclear physics and electron beam irradiation. In this talk, I will discuss the structure of BeamNetUS as well as the network’s efforts to create a streamlined process for engagement, with the aim of providing access to these facilities for groups without established connections. A program of awards evaluated through a competitive review process with a remit towards creating new, productive engagements will allow access to the facilities without cost for non-proprietary use in 2025.
LaserNetUS was launched in 2018, with a mission to advance and promote intense ultrafast laser science and applications. Since its inception, the network has transformed the landscape of high-power and high-intensity laser research, and it has grown into a community of over 1300 users. Additionally, it promotes worldwide collaborations and provides scientists, students, and underrepresented communities with broad access to unique facilities and enabling technologies. LaserNetUS has gone through 6 cycles of open calls for proposals, and over 130 unique experiments have been successfully executed across the network. Following on the success of LaserNetUS, other networks, such as beamNet, are launched to stimulate scientific discovery.
This talk will present LaserNetUS and scientific achievements across its 13 facilities over the first five years of operation, with particular emphasis on topics relevant for the AAC community. The breadth of laser parameters in pulse energy (from sub-Joule to a few kilojoules), pulse duration (from about 10 femtoseconds to 10s of nanoseconds) and repetition rate (up to 10 Hz) have enabled unique discoveries and applications in plasma-based particle acceleration, high energy density science, fusion energy, magnetic field generation, and plasma diagnostics. The talk will further present perspectives on the future of the network and how it can continue to stimulate high impact science in plasma physics, as well as in other scientific disciplines, medicine or industry.
The United States government high energy physics community develops state-of-the-art particle accelerator technologies, which later must be purchased from abroad to support domestic projects, because US-based firms are not consistently prioritized for government programs of record. In contrast, the high energy physics communities in Europe and Asia work to nurture their domestic industrial bases. Products developed by L3Harris Applied Technologies, Inc. (ATI) include large-scale pulsed power systems, commercial electron linacs for sterilization, high-power electromagnetic radiation systems, and flash X-ray radiography test equipment. ATI is an example of a domestic organization with complementary resources and capabilities for supporting the development and construction of the pre-injector linac for the Electron-Ion Collider (EIC) project. This presentation will provide a commercial perspective on how the US government high-energy physics community could engage US industry such that it would make business sense to continue operating in this space over a period of decades. Our shared goal is that domestic products and services will be available to support the next big US collider in the long term, as well as other accelerator facilities.
We report on electron-beam collimation using a passive plasma lens[1], integrated directly into a laser wakefield-accelerator stage operating in the high-charge regime. The lens is created by the reshaping of the gas-density profile of a supersonic jet at the beam’s exit side. It reduces the beam’s divergence by a factor of 2 to below 1 mrad (rms), while preserving the total charge of 170 pC and maintaining the energy spread. Ultrafast probing of plasma dynamics and Particle-in-Cell (PIC) simulations reveal that the effect is induced by the focusing field of the generated beam-driven wakefield as the remnant laser intensity drops significantly. The resulting spectral-charge density, defined here as the charge per energy bandwidth and emission angle, of up to 7pC/MeV mrad played a key role in the recent experimental demonstration of free-electron lasing[2]. The simple and robust gas-shaping technique presented holds the potential to generate specific density profiles, which are essential for the application of adiabatic focusing or staging of accelerators.
[1] Y.-Y. Chang, et al. “Reduction of the electron beam divergence of laser wakefield-accelerators by integrated plasma lenses“, Physical Review Applied 20, L061001(2023)
[2] M. Labat, J.P. Couperus Cabadağ, A. Ghaith, A. Irman, et al. “Seeded free-electron laser drive by a compact laser plasma accelerator” Nature Photonics 17, 150(2023)
Given a very short and intense plane-wave laser pulse travelling in the positive $z$ direction, we propose a multi-step preliminary analytical procedure to tailor the initial density profile $\widetilde{n_0}(z)$ of a cold diluted collisionless plasma to the pulse, so as to control the formation of the plasma wave (PW), its wave-breaking (WB) at density inhomogeneities, the self-injection of low-charge bunches of plasma electrons in the PW by the first WB at the density down-ramp, and to maximize the initial stages of the laser wakefield acceleration of the latter. The procedure consists in partially inverting our resolution procedure of the following direct problem: given $\widetilde{n_0}(z)$ and laser pulse, determine the motion of the plasma electrons. Such a resolution is based on a ``post-hydrodynamic" (i.e. multi-stream) fully relativistic plane model, which is valid as long as the pulse depletion can be negleted. Up to WB, we are able to reduce the Lorentz-Maxwell and electrons' fluid continuity equations to a family (parametrized by $Z\!>\!0$) of decoupled pairs of Hamilton equations for a 1-dimensional system. Here, $Z$ pinpoints the infinitesimal layer of electrons having coordinate $z\!=\!Z$ for $\!t\le\! 0$, $\xi=ct\!-\!z$ replaces time $t$ as the independent variable. To make the inversion formulae maneagable, we stick to slowly varying density profiles $\widetilde{n_0}(z)$. We check the effectiveness of the $\widetilde{n_0}$ resulting from the inversion formulae, and can then further improve it by fine-tuning, solving again the direct problem (first the equations of our plane model, then those obtained with Particle In Cell codes).
We report self-injecting LWFA driven by CPA-CO2 laser pulses of wavelength ~10 micrometers at Brookhaven's Accelerator Test Facility [1]. Long-wave IR pulses open opportunities to drive large wakes in low-density plasma more efficiently than near-IR pulses, potentially enabling higher-quality accelerated bunches. In experiments, 0.5-TW, 4-ps laser pulses generated no electrons, but drove self-modulated wakes characterized by optical scattering in plasma of density down to 4e17 cm-3, when peak power exceeded the critical power for relativistic self-focusing. 2-ps pulses with power up to 5-TW captured and accelerated electrons to relativistic energy in plasma of density as low as 3e16 cm-3. The shortest, most powerful pulses generated up to 0.4 nC total charge, including a collimated quasi-monoenergetic peak at ~10-MeV, along with a low-energy background. This marked the onset of a transition from self-modulated to the bubble regime. 3D Particle-in-cell simulations accurately predicted the thresholds for wake excitation and for self-injection, and other key details. The results portend future accelerators in which yet shorter, more powerful CO2 pulses drive plasma bubbles of ~300-micron radius, that can preserve the low emittance and energy spread of electron bunches injected externally from a synchronized low-energy linac.
[1] R. Zgadzaj et al., Nat. Commun. 15, 4307 (2024).
A tunable laser positron source as originally described in [1] is being prototyped using the collocated LWIR CO2 laser and electron beam at BNL-ATF. Unlike LPA, this work deals with interaction of three distinct entities, a laser, a pair-plasma, and laser-driven electron density structures.
This work relies on the advantages of larger size of electron density structures excited by the CO2 laser relative to NIR lasers at a given electron density, allowing more effective overlap with the pair-plasma in real space. Additionally, CO2 laser driven structures have a lower velocity for the same electron density, making possible longer interaction and greater energy exchange with the density structures.
The ATF electron beam that has mean particle energy of 55MeV, waist-size of 50-microns, bunch length 100fs with a high-Z metal target photo-produces the pair-plasma in a metal target of 15-25 mm length. The CO2 laser pulse which is collinear with the electron beam is focused onto a gas jet and the laser energy that propagates around the target excites electron density structures in the plasma. These electron density structures trap and exchange energy with the electron-positron pairs.
A positron source with nearly monoenergetic characteristics and pC charge has only been available at large accelerator complexes. Moreover, on-demand tunability of such positrons is only possible using the technique that we pursue. A compact, tunable laser positron source will open new possibilities in antimatter research [2].
[1] PRAB 21, 081301 (2018)
[2] US Patent 16,770,943
The plasma accelerator community has made significant progress in advancing particle beams, bringing us closer to realizing the dream of replacing the radio frequency (RF) cavities' MV/m fields with the plasma-sustained GV/m fields for collider applications. The beam requirements for realizing this vision emphasize a collider-quality beam featuring hundreds of pC of charge, energy spread less than 1%, and a normalized emittance less than 100 nanometers. Achieving the low-energy-spread of the beam during acceleration involves flattening the accelerating field within the wakefield region occupied by the beam, which can be accomplished if the charge per unit length of the injected electron beam to exhibit a trapezoidal profile. In this study, we demonstrate how novel techniques for controlling the spatiotemporal properties of a focusing laser pulse enable the optical injection of an electron bunch inside a plasma wakefield that meets all the beam requirements for collider applications. 3D particle-in-cell simulations demonstrate the feasibility of this method for producing beams exceeding 200 pC of charge with emittance and energy spread well within collider requirements.
Laser wakefield acceleration (LWFA) using laser-ablated metallic plasma targets has been developed for high-vacuum and high-repetition rate operations. The metallic plasma density (called the pre-plasma) generated by laser-ablation is increased via the optical ionization process due to intense fs laser pulse (called the main laser). The optical guiding of main laser in the plasma is influenced by the effects of the self-focusing, the self-compression, the optical divergence, and the ionization diffraction. Comparing with the case of helium plasma, the ionization injection occurred slightly earlier and the ionization diffraction is dominated so quickly. The strong diffraction allows the condition where the accelerating field become almost zero in a short time before the electrons may experience the dephasing field, keeping the energy spread of accelerated beam narrow.
We present and discuss the simulation results for high quality electron beam improved by the ionization effect: one is a structured metal target using two different metals to improve the beam charge and the dephasing-free condition for lower energy spread in a metallic plasma.
This work was supported by the National Research Foundation of Korea(NRF) grant founded by the Korea government(MSIT). (NRF Grant No. : NRF-2021R1A2C2094300, and RS-2022-0014317)
Laser-driven ion acceleration offers ultra-short (10s of fs for 10s of MeV), high-charge (100s of pC), and ultra-low slice emittance particle bunches. Mastering these sources can have a high impact on fundamental and applied research applications in physics, industry, and society, ranging from next-generation hadron colliders or neutrino factories, drivers for inertial fusion energy, radiotherapy, nuclear physics, warm-dense matter research, secondary radiation generation for material research and security applications, and possibly even radiation hardness of spacecraft. Despite clear progress in the last decades, particularly in the maximum ion energy using 1-10 Joule class laser systems, the desired energies for some applications still cannot be reached. Relieving the requirements imposed by a single laser-ion source, we present a staging concept that boosts a proton beam into the desired energy regime of 100s of MeV/u within a few compact, beam-quality-preserving plasma stages. Our approach is based on magnetic vortex acceleration, using near-critical density targets with a pre-formed hollow channel to boost the energy of a temporally matched ultra-intense proton bunch. With fully self-consistent 3D particle-in-cell simulations using the exascale code WarpX, we demonstrate robustness in bunch acceptance (temporal and spatial), transport, energy boost, energy spread, and emittance preservation, using current and near-term available laser-system parameters.
High-energy, spin-polarized particles are of great interest for a variety of applications like deep-inelastic scattering for the investigation of the proton nuclear structure or fusion, where the use of polarized reactants can increase the fusion cross-section. Acceleration of such particles via laser-plasma interaction can prove to be difficult, as the target needs to be pre-polarized. This rules out solid-state based mechanisms. Further, strong laser fields can induce depolarization. Thus, novel acceleration schemes are required to ensure a significant degree of polarization.
In this talk, we will present an overview of the state-of-the-art for the acceleration of spin-polarized protons. Two acceleration mechanisms, Magnetic Vortex Acceleration [1] and Collisionless Shock Acceleration [2], will be investigated by means of particle-in-cell simulations. The two schemes prove to be feasible options for producing highly polarized ion beams even for parameters of near-future laser facilities.
[1] L. Reichwein et al., Phys. Rev. Accel. Beams 25, 081001 (2022)
[2] L. Reichwein et al., Plasma Phys. Control. Fusion 66, 055002 (2024)
Traditional linear accelerators (LINACS) are effective for accelerating large amounts of ion charge with high efficiency. However, their compactness is limited by the breakdown of the solid accelerating structure, typically on the order of MV/m. On the other hand, laser-target ion accelerators can produce much higher accelerating field, e.g. via a TNSA mechanism, but are limited in the resulting ion energy gain by the small size of their acceleration region. In this talk I will revisit and extend the concept of Ionization Front Acceleration (IFA), first introduced in the 1980s. The IFA approach combines the compactness of laser plasma ion accelerators with the high efficiency, brilliance, and extended acceleration distances characteristic of traditional LINACS. In this scheme, an intense relativistic electric beam is directed into a gas medium, while a sweeping external laser ionizes the gas, propelling the ionization front forward. This creates an acceleration region with gradients of sub-gigavolt per meter(~300MV/m) that co-propagates with the injected ions, offering the potential for a compact, high-yield ion accelerator. Using particle-in-cell simulations, we demonstrate the acceleration of 150 MeV few-μC hydrogen ions over a distance of < 0.5m. Additionally, we propose an innovative scheme, termed Counter-propagating Laser-Ionization Front (CLIF) acceleration, to overcome the hosing instability of the driver beam that limits the final energy -- a potential challenge that was not explored in the earlier IFA research.
We assess the conversion efficiency from intense picosecond laser pulses to multi-MeV ion beams for a wide range of laser and target parameters,using 2D kinetic particle-in-cell simulations. Scalings are addressed in a quasi-one-dimensional geometry, leaving out beam divergence. Then, we study the conversion efficiency into a narrow spatial band along the laser axis for flat and hemispherical targets in large-scale 2D simulations. Combining these findings allows us to calculate the energy requirements for ignition of a compressed ICF target with an intense proton beam in a fast-ignition scenario.
This work was funded under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract No. DE-AC5207NA27344 with support from the Laboratory Directed Research and Development Program under tracking code 23-ERD-023
A new paradigm based on oscillations of quantum gas of conduction band electrons known as plasmons has opened unprecedented PetaVolts per meter fields [1,2,3,4]. PV/m fields can be attained using a class of non-perturbative plasmons uncovered in our work. This class of plasmons is excited by particle beams launched inside a conductive tube which makes it possible to control the excitation of large-amplitude oscillations up to the extreme limits while also mitigating various instabilities. We pursue extreme plasmons [2,5] for future high energy physics (HEP) accelerators and gamma-ray lasers through a dedicated experimental program at the SLAC national lab. The unparalleled field frontier enabled by extreme plasmons, also carries a great appeal for non-collider examinations of HEP. Our first experiments will characterize extreme plasmons in semiconductors doped to match with the FACET-II electron beam, paving the way towards broader goals outlined above.
[1] Sahai, A. A., Nanomaterials Based Nanoplasmonic Accelerators and Light-Sources Driven by Particle-Beams, IEEE Access, 9, pp. 54831-54839 (2021).
[2] Sahai, A. A., Extreme plasmons, arXiv:2404.02087 (2024).
[3] Sahai, A. A., Nanostructure nanoplasmonic accelerator, high-energy photon source, and related methods, PCT WO2021216424A1, WIPO (2021).
[4] Sahai, A. A., Golkowski, M., Katsouleas, T., et. al., Approaching PetaVolts per Meter Plasmonics Using Structured Semiconductors, IEEE Access, 11, pp. 476-493 (2023).
[5] Sahai, A. A., Golkowski, A. A., et. al., PetaVolts per meter Plasmonics: introducing extreme nanoscience as a route towards scientific frontiers, Journal of Instrumentation 18, P07019 (2023).
Plasma wakefield accelerators (PWFA) have showcased remarkable acceleration gradients, reaching tens of GeV per meter. Advancements in generating high-quality beams via self-injection schemes and pursuing attosecond electron beams represent the forefront of this field. In this work, we introduce a novel approach to inject a high-quality electron beam using beam-induced ionization injection (B-III) with a driver-injector beam configuration. In B-III, the field of a particle beam intensifies as its slice envelope oscillates towards its minimum value due to the betatron oscillation, whereby it further ionizes electrons of an impurity element for subsequent injection. We will explain the physical underpinnings of this design using analytics plasma wakefield theory and present supporting Particle-In-Cell (PIC) simulation results that show the potential for creating an injected beam with ~500 attosecond duration, hundreds of nanometer emittance, and less than 1% energy spread. Furthermore, we will present the prospect of realizing this beam experimentally at FACET II, where the desired driver-injector beam configuration would be attained by control over compression and selection of the beam phase space using a collimator. This technique is routinely performed for generating two beams in drive-trailing PWFA experiments at FACET II. Results from Lucretia, a physics toolbox simulating electron beam through FACET-II transportation line, will be presented to demonstrate the feasibility of generating the required drive-injector beam. Finally, we will present the potential application of the injected beam in generating attosecond Free Electron Laser (FEL).
We demonstrate through high-fidelity particle-in-cell simulations a simple approach for efficiently generating 20+ GeV electron beams with the necessary charge, energy spread, and emittance for use as the injector for an electron arm of a future linear collider or a next generation XFEL. The self-focusing of an unmatched, relatively low quality, drive beam results in self-injection by elongating the wakefield excited in the nonlinear blowout regime. Over pump depletion distances, the drive beam dynamics and self-loading from the injected beam leads to extremely high quality and high energy output beams.For plasma densities of 10^18 cm-3, PIC simulation results indicate that self-injected beams with 0.52 nC of charge can be accelerated to ~20 GeV energies with projected energy spreads < 1% within the beam core, slice normalized emittances as low as 110 nm, peak normalized brightnesses > 10^19 A/m^2/rad^2, and energy transfer efficiencies of >54%.
This work was supported by US NSF grant No. 2108970 and US DOE grant No. DE-SC0010064.
High-brightness electron bunches drive fundamental research in particle physics and photon science. Key to achieving a high brightness is to have a low transverse emittance. In radiofrequency accelerators a low initial emittance can be rapidly degraded due to space-charge forces, which are greatly diminished once the electron bunch attains relativistic velocity. A plasma accelerator can maintain orders-of-magnitude higher accelerating fields than radiofrequency accelerators, while multiple techniques exist to create a low-emittance electron bunch directly inside the plasma accelerator structure. Plasma accelerators therefore offer the opportunity to take a comparatively lower-brightness electron bunch produced by a radiofrequency accelerator, and use it to drive a wakefield which traps and accelerates a significantly higher brightness electron bunch. Here we demonstrate the injection and gigavolt-per-metre acceleration of a bunch with a 3D brightness 4.8 times greater than that of the driver. The injected bunches had high reproducibility, 1 mm-mrad normalised emittance, order 10 pC/MeV spectral densities and per-cent-level energy spreads.
Plasma-based acceleration (PBA) has emerged as a promising candidate for the accelerator technology used to build a future linear collider and/or an advanced light source. In PBA, the witness beam needs to be matched to the focusing forces of the wakefield (WF) to reduce the emittance growth. In some linear collider designs, the matched spot size of the witness beam can be 2 to 3 orders of magnitude smaller than the spot size (and wavelength) of the WF. Such an additional disparity in length scales is ideal for mesh refinement where the WF within the witness beam is described on a finer mesh than the rest of the WF. We describe a mesh refinement scheme that has been implemented into the 3D QS PIC code, QuickPIC. A fast multigrid Poisson solver has been implemented for the field solve on the refined meshes and a Fast Fourier Transform (FFT) based Poisson solver is used for the coarse mesh. A series of intermediate meshes are used to improve accuracy. The code has been parallelized with both MPI and OpenMP, and the parallel scalability has also been improved by using pipelining. An adaptive mesh refinement technique is implemented to optimize the computational time for simulations with an evolving witness beam size. Several test problems are used to verify that the mesh refinement algorithm provides accurate results. The results are also compared to highly resolved simulations with near azimuthal symmetry using a new hybrid QS PIC code QPAD.
Longitudinal bunch shaping is one of the important challenges for collinear wakefield acceleration due to its impact on acceleration efficiency. While shaping both drive and main beams is important, shaping drive beam is particularly challenging due to the stringent requirement for high charge to achieve a high gradient. The challenge is usually originated from the Coherent Synchrotron Radiation (CSR), which is unavoidable in beamlines using dipole magnets. Several years ago, a method using transverse deflecting cavities (TDC) was introduced to fully avoid the CSR effect on the shaping process. Our collaboration plans to demonstrate the concept in the near future. Once the demonstration is completed, we plan to experimentally investigate the relationship between the transformer ratio and the gradient. Furthermore, we aim to demonstrate high-gradient (~100 MV/m) and high transformer ratio (~90% of ideal) simultaneously. We present the status and preliminary simulation results.
Two-beam acceleration is a powerful method to generate high accelerating fields by utilizing short radiofrequency pulses. The Argonne Wakefield Accelerator facility is applying a two-beam acceleration approach to an X-band radiofrequency gun. This gun has experimentally demonstrated an electric field on the photocathode of ~400 MV/m. The next phase of this experiment will involve adding a short X-band linac to boost the beam energy up to ~10 MeV. This paper summarizes the optimization of the linac and beam dynamics simulations in the integrated system over a wide range of operating parameters and demonstrates that the available setup will support the generation of bright or ultrashort beams with possible applications to compact light sources including inverse Compton scattering.
Because of their ability to produce high gradients, radiofrequency (RF) structures in the sub-terahertz (sub-THz) regime are of considerable interest in structure wakefield acceleration. These structures can be used to generate a high gradient and high efficiency wakefield, allowing for a low physical footprint. In the pursuit of a structure with these properties, we have designed and built a metallic corrugated W-band structure based on the available electron beams at the Argonne Wakefield Accelerator (AWA) with the emittance exchange (EEX) beamline. The EEX beamline offers the possibility to perform longitudinal bunch shaping to optimize the gradient and the transformer ratio (defined as the accelerating gradient at the witness bunch over the decelerating gradient at the drive bunch in the two-beam acceleration regime). This talk will present the testing results of the W-band structure when excited by 42 MeV bunches sent through the EEX beamline. Two cases were studied: (1) demonstration of a high gradient from a single drive electron bunch with a charge of 10 nC and a short bunch length of about 150 microns; (2) demonstration of a high transformer ratio using a two-bunch train, where the drive bunch with about 2 nC of charge was shaped with a transverse mask, and a small witness bunch trailed behind to measure the wakefield. Detailed results will be presented in this talk, showcasing the promise of sub-THz wakefield acceleration with longitudinal bunch shaping.
The generation of high spectral brilliance radiation with electron beam sources relies heavily on the qualities of the electron transverse emittance and its longitudinal compression which significantly affect X-ray generation efficiency in Inverse Compton Scattering. Designing and building such a system in a compact formfactor requires non-trivial solutions starting from electrons generation and ending with the interaction region. RadiaBeam has designed, built and tested a compact photoinjector with a hybrid RF structure combining standing wave and traveling wave components in a C-band configuration. The standing wave section facilitates high-field acceleration from the photocathode, while the traveling wave portion induces strong velocity bunching. This remarkably compact injector system offers the additional advantage of simplifying the distribution of RF power by eliminating the need for the RF circulator. We explore the application of this device in a compact 4.5 MeV electron source for further acceleration up to 100 MeV, enabling both inverse Compton scattering and free-electron laser radiation sources with distinctive and appealing properties.
In this work we review the commissioning of this high field hybrid photoinjector electron source. Step-by-step process of achieving first photoelectrons, performing beam-based alignment, characterizing photocathode quantum efficiency and measuring electron beam parameters such as energy gain and spread, bunch length, charge yield and emittance value are described within the scope of this work. Reported findings substantiate the foundation for further harnessing hard X ray from inverse Compton scattering of the IR laser with 100 MeV electron beam.
Structure-based wakefield acceleration (SWFA) is a proposed concept to overcome limitations in conventional accelerators. This approach allows for the creation of short-input radiofrequency (rf) pulses, which have been empirically shown to reduce breakdown rates at a given gradient. Metamaterial structures with negative group velocity have shown promise in accelerator applications. A structure wakefield experiment, with a metamaterial accelerator, exploited the direct benefits of operation in the short-pulse regime because of the existence of an operational regime, the breakdown-insensitive acceleration regime (BIAR), where disturbances in secondary pulses are observed but the main acceleration pulse is still intact. In this talk, the experimental results and dark current simulations of the metamaterial accelerator will be presented.
RF breakdown limits the attainable acceleration gradient in normal conducting RF structures, challenging high-gradient operations. Recent experiments at the Argonne Wakefield Accelerator (AWA) suggests short RF pulses (a few nanoseconds) can mitigate this breakdown. We simulated dark current emission in the short-pulse regime to study breakdown initiators including field emission and multipacting. This study integrates analytical and numerical modeling of dark electron generation to understand multipacting and RF breakdown in structures driven by short RF pulses. We simulated electron trajectories under various conditions in the electromagnetic fields. Our analytical model, compared against simulations, predicted multipacting resonance modes and secondary electron yield. Our findings have revealed the dependence of dark current generation on the RF field strength, pulse duration, and surface properties. These insights guide the design of RF structures with enhanced performance and reduced breakdown susceptibility, advancing the next-generation short-pulse accelerators.
We consider to develop GeV-level high-gradient linacs. These accelerators will be based on an short-pulse cryogenically cooled copper technology that will provide a gradient of 300 MV/m or higher. Since there is a shortage of high-power nanosecond RF sources, we propose the development of the pulse compression methods. Instead of passive pulse compressors like SLED, SLED-II and its recent modifications requiring broad bandwidth klystrons we focus on active RF switches. In our review we compare RF switches based on different principles including plasma switches, semiconductor switches, ferroelectric switches, and switches based on electron beam injection in an RF resonator. We come to the conclusion that the last mentioned type of switches is not vulnerable to a multipactor and it is most appealing for a high-gradient acceleration.
In this talk we will present results from high gradient structure testing of single, multi-cell and meter-scale accelerating structures. Structures were tested with a variety of fabrication techniques including brazing, diffusion bonding and clamped plated structures. Target gradients of 120 MeV/m were achieved and exceeded. Designs and performance of rf components (loads, windows, etc.) for these tests will also be discussed. Plans for future experiments will be presented.
Recently, a new method was proposed that uses transverse wigglers to generate arbitrary correlation in phase space. Each wiggler imparts a sinusoidal modulation with a designed amplitude, period, and phase, which can serve as a basis for approximating the desired correlation. While correlation control includes the majority of existing beam manipulations, it has mostly been limited to relatively simple correlations. Since the new method can handle much more complex correlations, it could enhance the performance of existing methods and enable new opportunities. In this talk, I will present several applications of 2D correlation generation using transverse wigglers.
An emittance exchange (EEX) beamline may provides a unique capability in transferring a transverse beam density modulation into longitudinal bunching. This process can be advantageous for achieving coherent bunched current at below the micron level. This can provide conditions of super-radiance in a radiating system, or a large input signal for a high gain the FEL process. This mechanism has been proposed to enable FEL action down to the few nm scale for future facilities. We investigate the feasibility of creating longitudinal density modulation at the Argonne Wakefield Accelerator, beginning with the case of 800 nm bunching in a pC-level beam. We discuss plans for modulated beam creation, collective and nonlinear effects the EEX beamline and subsequent radiation-based diagnosis via CTR or FEL processes.
Precise control of the longitudinal distribution of an electron beam enables new opportunities for accelerator applications, such as high transformer ratio plasma wakefield acceleration or reduced beam degradation from the microbunching instability. Electron beam shaping can be achieved through the use of a laser heater which exploits the coherent interaction between a laser pulse and an electron beam in a magnetic undulator to increase the beam’s slice energy spread. By tailoring the properties of the laser heater, it is possible to modulate the beam’s current profile on-demand, enabling the generation of designer electron beams tuned for specific applications.
We present the experimental results of using a laser heater to manipulate the electron current profile at the FACET-II facility. We demonstrate the impact of the laser heater’s temporal profile on shaping the beam current, with an emphasis on the production of fs-duration current spikes with ultra-high ~0.1 MA peak current. Using these beams, we observe the enhancement or controlled suppression of beam-driven ionization in a He gas target. These beams have further been used to benefit the broader science program at FACET-II including aiding experiments studying narrow plasma column generation, density down ramp injection and probing the transition between wakeless and plasma-wakefield regimes. Our combined simulations and experiments offer an improved understanding of the generation and potential applications of such current spikes, providing another approach for optimizing advanced accelerator performance for future applications.
Laser-plasma accelerators (LPAs) offer an attractive alternative to conventional accelerators, enabling the acceleration of high-brightness electron beams to ultra-relativistic energies using compact, table-top setups. However, LPAs and their applications are plagued by intrinsic shot-to-shot instability largely attributed to fast fluctuations (>1 Hz) and long-term drifts (<1 Hz) in the driving laser system. Specifically, fluctuations in the final focus longitudinal position result in correlated instability in LPA electron beam qualities, particularly for targets with precision tailored longitudinal profiles. We present a scheme for active stabilization of the longitudinal focal position for a 100 TW laser system, which involves noninvasive wavefront monitoring of the unamplified kHz pulse train and correction implementation via an upstream telescopic lens on millisecond timescales. This approach has demonstrated marked improvements in long-term LPA operation and shot-to-shot stability in terms of generated charge quantity and electron beam spectral content.
This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of High Energy Physics, under Award Number DE-SC0021680 and Prime Contract No. DE-AC02-05CH11231.
Conventional beam-transport optics, such as quadrupole magnets, are problematic for staging of plasma accelerators, mainly due to their footprint and chromaticity. This causes emittance growth and potentially charge loss. Based on the results obtained by Steinke et al. [1] and further developments on plasma lenses by Lindstrøm et al. [2], we propose an achromatic lattice using a new type of optics element: a non-linear plasma lens with a transversely tapered B-field across its radius (a focusing and sextupole-like field). This device uses the Hall effect of an external transverse B-field on a longitudinal discharge current [3]. A prototype design is presented, with an experimental demonstration planned for 2024-2026 at the CLEAR electron test facility at CERN. This work is part of the ERC StG project SPARTA [4] at the University of Oslo.
[1] Steinke, S. et al. (2016). Multistage coupling of independent laser-plasma accelerators. Nature, 530, 190-193.
[2] Lindstrøm, C. A. et al. (2018). Emittance preservation in an aberration-free active plasma lens. Physical Review Letters, 121, 194801.
[3] Kunkel, W. B. (1981). Hall effect in a plasma. American Journal of Physics, 49, 733-738.
[4] European Commission - Staging of Plasma Accelerators for Realizing Timely Applications, https://doi.org/10.3030/101116161
Recent progress in plasma-based accelerators has sparked intense interest in developing plasma-driven free-electron lasers [1]. However, operating free-electron lasers at soft and hard X-ray wavelengths necessitates electron beams with significantly enhanced 6D brightness. The author outlines comprehensive strategies for producing ultrahigh 6D brightness electron beams in beam-driven plasma wakefield acceleration (PWFA). These ultrahigh 6D brightness electron beams have the potential to enable new photons and fundamental science capabilities [2]. One immediate ramification of this new class of electron beams is a blueprint for an ultra-compact attosecond-Angstrom class free-electron laser [3]. Additionally, the author will discuss how these high-brightness PWFA stages can augment the capabilities and functionalities of current and future linac-based free-electron lasers.
[1] Graydon, O. Nat. Photon. 16, 750–751 (2022).
[2] Habib, AF et al. Annalen der Physik 535.10,p. 2200655 (2023)
[3] Habib, AF et al. Nat. Commun. 14, 1054 (2023)
Recent high repetition rate lasers capable to produce TW peak power, few-cycle laser pulses with 100 W average power at industrial standards. Hence, they may offer an alternative to the PW peak power lasers for applications that need a quasi-continuous source of neutrons.
The SEA laser of ELI-ALPS delivered 21 mJ, 12 fs laser pulses at 10 Hz repetition rate on the target. Deuterons were accelerated from the interaction of the laser with an ultrathin heavy water leaf to energies around MeV, which then induced 2H+2H fusion reaction in a deuterated polyethylene disk. The resulting fast neutrons (around 2.5 MeV) were measured with three independent detection systems. Three independent detection systems were used for measuring the neutron yield and distribution. A time-of-flight (ToF) detector system, within which each detector consisted of a plastic scintillator and a photomultiplier; a liquid scintillator, the ToF signal of which was evaluated with the pulse shape discrimination method; and a bubble detector spectrometer calibrated against a conventional PuBe source. The system operated with high stability (10%) for several hours in each day, resulting in a neutron yield of 1.5×10^5 neutron/s.
Most recently, stable ion acceleration has been also demonstrated at 1 kHz repetition rate with 35 mJ, sub-10 fs laser pulses. The highest neutron yield so far (10^8 neutron/s) was achieved with 80 mJ laser pulses on target for a few minutes, too. The paper also outlines one of the first related applications, i.e. the irradiation of zebrafish embryos with such laser-generated neutrons.
The ion channel laser (ICL) is similar to the free electron laser (FEL) but utilizes the electric field from a blowout regime plasma wake rather than the magnetic field from an undulator to oscillate particles. Compared to the FEL, the ICL can lase with much larger energy spread beams and in much shorter distances, making it an attractive candidate for a future compact plasma accelerator driven coherent light source. We present a novel full 3D theory of the ICL accounting for numerous effects including transverse guided mode shape, diffraction, frequency and Betatron phase detuning, and nonzero spread in energy and undulator parameter. This theory is used to predict the gain, radiation mode profile, gain bandwidth, and emittance and energy spread constraints of the ion channel laser.
The generation of high-energy photons is a useful diagnostic tool in many different contexts. In laser-solid target experiments, the total yield and energy distribution can be compared for different target types to determine the optimal set-up for photon generation, to be used in radiography and computed tomography of dense objects. In colliding experiments between a laser pulse and an electron beam, the change of the photon yield with different experimental parameters can help differentiate between various radiation sources. In addition, the spectral data can help benchmark particle-in-cell (PIC) simulation codes that describe quantum electrodynamic (QED) processes. As higher-power laser facilities are opening, these types of experiments will be able to explore new regimes of physics and generate photon spectra extending to higher energies. Therefore, it’s important to develop diagnostic tools capable of making these measurements. Spectrometers such as the filter stack spectrometer (FSS), the scintillator attenuation spectrometer (SAS), and the gamma stack spectrometer (GSS) have been used in several experiments at the Texas Petawatt Laser facility (TPW) and ELI-NP, providing valuable data about photon production at different laser energies. By using knowledge of the strengths and weaknesses of these spectrometers, we are developing a novel multi-channel scintillator array to work at a high repetition rate that improves our ability to unfold the spectrum from the measured signal. Its modular design will allow it to be utilized in a range of experiments at ZEUS and other laser facilities.
We are utilizing a sub-ps, sub-10 micron X-ray source for X-ray phase contrast imaging (XPCI) tomography of Inertial Confinement Fusion (ICF) fuel capsules). We will present results from an experiment in April 2024 at the Advanced Laser Light Source in Montreal, Canada. Radiography data was captured with Laser Wakefield Acceleration blowout regime betatron X-rays with a critical energy of 15-25 KeV. Experimental goals met include imaging 360 degrees of an ICF fuel capsule, and benchmarking optimal resolution parameters of the system. Imaging the full rotation of the object will allow us to do a tomographic reconstruction of these fuel capsules with a resolution of ~4 um. The optimal resolution benchmarked is ~1um, which is comparable to current methods. We use X-ray phase contrast imaging to differentiate between thin low Z layers in the ICF fuel capsule. The Fresnel-Kirchoff integral formula can be used to determine source characteristics from XPCI fringes seen in radiographs1, we will also employ HADES (an X-ray ray tracing simulation code). The results of this experiment provide a comparison of current industrial methods such as X-ray tubes to LWFA based X-ray sources. Ultimately, our aim is to develop a diagnostic for not just target metrology of ICF fuel capsules, but employable to observe ICF implosions with unprecedented spatio-temporal resolution.
This work was performed under the auspices of the Lawrence Livermore National Security, LLC, (LLNS) under Contract No. DE-AC52-07NA27344.
References
[1]Vargas, X-ray phase contrast imaging of additive manufactured structures using a laser wakefield accelerator. PPCF, 61 (2019) 054009.
An x-ray excitation in a medium can cause localized heating (<mK) and thermoelastic expansion, inducing a detectable ultrasonic emission which potentially enables low-dose, 3D imaging [1]. For effective ultrasonic emission, the dose should be deposited faster than the stress confinement time of the medium, ~ns for many applications. This modality has been studied in medical linear accelerators (LINAC’s) [2] and more recently in a synchrotron [3]. LINAC’s suffer from long pulses (~μs) and synchrotrons, although successful, are not viable for this application due their size and cost. Laser Wakefield Accelerators (LWFA’s), on the other hand, produce femtosecond radiation and are more readily available, making them a candidate to explore XACT. Here, we compare Monte Carlo (GEANT4) simulated dose deposition [4] and acoustic responses from Inverse-Compton scattering radiation, Bremsstrahlung radiation and electrons (all these sources generated by a LWFA) for two applications: (1) imaging of metallic markers in water and (2) imaging of a cortical-trabecular bone configuration embedded in water. Advantages from each radiation source are discussed.
[1] Samant, P., et al. X-ray induced acoustic computed tomography, Photoacoustics 19, 100177, https://doi.org/10.1016/j.pacs.2020.100177 (2020)
[2] Xiang, L., et al. X-ray acoustic computed tomography with pulsed x-ray beam from a medical linear accelerator, Med. Phys. Lett. 40 (1) http://dx.doi.org/10.1118/1.4771935, (2013).
[3] Choi, S., et al. Synchrotron X-ray induced acoustic imaging, Scient. Rep. 11:4047, https://doi.org/10.1038/s41598-021-83604-3. (2021).
[4] Agostinelli, S. et al. GEANT4 – a simulation toolkit, Nucl. Instrum. Methods Phys. Res. Sect. A Accel. Spectrom. Detect. Assoc. Equip, 506, 250-303, https://doi.org/10.1016/S0168-9002(03)01368-8 (2003).
The Accelerator Test Facility (ATF) at Brookhaven National Laboratory is a DOE Office of Science User Facility that offers users three major beam capabilities: 75 MeV high-brightness electron beams, multi-terawatt long-wave infrared (LWIR) laser beams, and near-infrared (NIR) laser beams. A primary research focus for ATF users is the study of laser wakefield acceleration (LWFA) driven by an LWIR laser, which can efficiently generate macroscopic plasma bubbles. With the facility's provision of low-emittance and low-energy-spread relativistic electron bunches from a conventional linac, ATF provides an ideal setting for investigating LWFA seeding, phasing, and staging issues.
This discussion highlights recent and upcoming advancements at the ATF to meet the required laser and electron beam parameter ranges for exploring the most promising LWFA regimes pertinent to future colliders built upon laser-plasma accelerator (LPA) stages.
Research is in progress to develop high efficiency RF sources for driving accelerators and colliders. These include a 350-450 MHz multiple beam triode, a single beam klystron at L-Band, and a multiple beam klystron at C-Band. The goal efficiency for these devices is 80% or better.
A single beam klystron estimated to operate at 80% has been built and is awaiting testing. The klystron uses a COM-type circuit and is designed to produce 200 kW CW at 1.3 GHz. The tube is approximately ten feet long and presented several challenges for assembly and handling.
Research is continuing on a multiple beam triode-based RF source to produce 200 kW CW between 350 – 700 MHz. If successfully developed, this would provide the lowest cost, most compact RF source in this frequency and power range. The efficiency is estimated at 80%, and the cost would be approximately 50 cents per watt, which less than a fourth the cost of a comparable klystron or solid state system.
A multiple beam klystron at C-Band was designed to produce 200 kW CW at 5.8 GHz using six beams to reduce the operating voltage. The program goal is an interaction efficiency exceeding 80%, which was achieved computationally using a COM circuit. The tube would operate at 45 kV with a microperveance of 0.1. The primary challenge was achieving high beam quality for the six electron beams. A proposal is being reviewed to provide funding to complete the design and build and test the klystron.
In its 2023 report, the Particle Physics Project Prioritization Panel states a long-term objective to develop a 10 TeV parton center-of-mass collider to probe the parameter regime beyond the standard model. It is furthermore emphasized that wakefield accelerators should be explored as a technology to provide such high energies in a e+e- or gamma-gamma-collider scenario. As a consequence, the advanced accelerator community is encouraged to evaluate different methods and their applicability towards this ambitious goal.
In a recent paper, laser-gated PWFAs have been suggested as a method to minimize inter-stage space requirements in multi-stage plasma-accelerator up to 1 TeV of electron-beam energy [1]. We will discuss the scheme’s advantages and difficulties in the context of a 10 TeV parton center-of-mass collider.
High intensity laser facilities are expanding their scope from laser and particle-acceleration test beds to user facilities and nuclear physics experiments. A basic goal is to confirm long-standing predictions of strong-field quantum electrodynamics, but with the advent of high-repetition rate laser experiments producing GeV-scale electrons and photons, novel searches for new high-energy particle physics also become possible. The common figure of merit for these facilities is the invariant $\chi\simeq 2\gamma_e|\vec E_{\rm laser}|/E_c$ describing the electric field strength in the electron rest frame relative to the ``critical'' field strength of quantum electrodynamics where the vacuum decays into electron-positron pairs. However, simply achieving large $\chi$ is insufficient; discovery or validation requires statistics to distinguish physics from fluctuations. The number of events delivered by the facility is therefore equally important. In high-energy physics, luminosity quantifies the rate at which colliders provide events and data. We adapt the definition of luminosity to high-intensity laser-electron collisions to quantify and thus optimize the rate at which laser facilities can deliver strong-field QED and potentially new physics events. Modeling the pulsed laser field and electron bunch, we find that luminosity is maximized for laser focal spot size equal or slightly larger than the diameter of the dense core of the electron bunch. Several examples show that luminosity can be maximized for parameters different from those maximizing the peak value of $\chi$ in the collision. The definition of luminosity for electron-laser collisions is straightforwardly extended to photon-laser collisions and lepton beam-beam collisions.
Several collider technologies, including plasma-based technology, have been proposed for a future 10 TeV COM collider. A major challenge for these machines is maintaining the target luminosity while mitigating the adverse effects of disruption, beamstrahlung, and background generation. Therefore, comprehensive beam crossing simulation are essential to fully understand the physics at the interaction point. We show that WarpX, an Exascale open-source code Particle-In-Cell code, can be used for beam-beam studies. WarpX offers high performance, portability across different operating systems and multi-CPU/GPU architectures, flexibility with various options, algorithms, and diagnostics, and is supported by thorough documentation and regular maintenance from a large, active, and multi-disciplinary community. We provide benchmarks comparing WarpX to established codes like GUINEA-PIG and CAIN, and present initial simulation results for plasma-based colliders.
Plasma acceleration has emerged as a promising technology for future particle accelerators, particularly linear colliders. Significant progress has been made in recent decades toward high-efficiency and high-quality acceleration of electrons in plasmas. However, this progress does not generalize to the acceleration of positrons, as plasmas are inherently charge asymmetric. Here, we present a comprehensive review of historical and current efforts to accelerate positrons using plasma wakefields [1]. Proposed schemes that aim to increase energy efficiency and beam quality are summarized and quantitatively compared. A dimensionless metric that scales with the luminosity-per-beam power is introduced, indicating that positron-acceleration schemes are currently below the ultimate requirement for colliders. The primary issue is electron motion; the high mobility of plasma electrons compared to plasma ions, which leads to nonuniform accelerating and focusing fields that degrade the beam quality of the positron bunch, particularly for high efficiency acceleration. Finally, we discuss possible mitigation strategies and directions for future research.
[1] G. Cao et al, "Positron acceleration in plasma wakefields" Phys. Rev. Accel. Beams 27, 034801 (2024)
Kinetic simulations of relativistic, charged particle beams and advanced plasma accelerator elements are often performed with high-fidelity particle-in-cell simulations, some of which fill the largest GPU supercomputers. Self-consistent modeling of wakefield accelerators for colliders includes many elements beyond plasma acceleration. The integrated Beam, Plasma & Accelerator Simulation Toolkit (BLAST) provides high-performance simulation codes suitable to model different parts of a beamline on the latest and world's largest GPU supercomputers. Yet, for some workflows such as start-to-end modeling and coupling with experimental operations (digital twins), it is desirable to integrate and model all accelerator elements with very fast, effective models. Traditionally, analytical and reduced-physics models fill this role, usually at a cost of lower fidelity and/or reduced dynamics.
Here, we show that the vast data from high-fidelity simulations and the power of GPU-accelerated computation open a new opportunity to complement traditional modeling: data-driven surrogate modeling through machine learning (ML). We present the new capabilities for fully GPU-accelerated, in-the-loop ML workflows in BLAST and how they complement and fill a need alongside first-principles modeling and reduced models and pair well with recently established out-of-the-loop machine-learning workflows (i.e., optimization). We demonstrate that the high-quality data from WarpX simulations can train low-error surrogate data models, which are seamlessly integrated into a GPU beamline simulation using ImpactX, with the purpose of minimizing chromatic emittance growth during acceleration and transport in a staged laser-wakefield accelerator of low beam charge.
ALEGRO, the Advanced LinEar collider study GROup, is an international study group created in 2017 to promote Advanced and Novel Accelerators (ANAs) for High-Energy Physics applications. It is driven by the ICFA-ANA panel. ALEGRO organizes workshops (CERN 2017, Oxford 2018, CERN 2019, DESY 2023, IST 2024) to energize the ANA community around applications to particle and high-energy physics. The implementation by the laboratory Directors Group (LDG) of a roadmap for ANAs is taking place in the context of the European Strategy for Particle Physics (ESPP). It is centered around existing international programs: AWAKE, EuPRAXIA and HALHF. In the US, the P5 has recently recommended the design of a 10TeV CM lepton collider or of a 100TeV pCM hadron collider.
The goals of the ALEGRO 2024 Workshop at IST were to take stock of progress with ANAs, and to initiate a world-wide effort on the design of a 10TeV CM, ANA-based lepton collider.
The first goal was addressed by inviting speakers to present recent scientific results. The second one was addressed through sessions in which major participants in the ESPP and P5 processes summarized the implementation of the recommendations and roadmaps that emerged from these processes. Also, invited speakers described major ANA-related programs and facilities addressing challenges related to collider development.
A document summarizing the outcome of the workshop and the presentations will be generated.
I will report on the 2024 workshop at IST. I will also outline the status of the international collaboration to develop an ANA-based collider concept.
I will give an overview of the 2023 P5 recommendations for accelerators as well as rollout plans, processes, recent HEP organizational changes and possibly share some personal perspectives and thoughts.
This discussion focuses on the planning for R&D toward a linear collider based on advanced acceleration concepts.
Boxed Lunches provided. Grab and Go