2nd Workshop on Microwave Cavities and Detectors for Axion Research

10 Jan 2017, 08:00 → 13 Jan 2017, 18:00 US/Pacific

LVOC - Yosemite Room (Lawrence Livermore National Laboratory)

Gianpaolo Carosi (Lawrence Livermore National Laboratory), Gray Rybka (University of Washingont)

Lawrence Livermore National Laboratory (LLNL) will be hosting the 2nd in a series of Workshops on Microwave Cavities and Detectors for Axion Reserch at the Livermore Valley Open Campus January 10-13th, 2017. Discovering the nature of dark matter is one of the major research efforts for DOE High Energy Physics. Primordial axion particles are a primary dark matter candidate and the most sensitive search techniques use resonant microwave cavities to convert the axions into detectable photons. These cavities are highly specialized and must operate in large magnetic fields at ultra-low temperatures. This workshop focuses on variety of unique design issues for these microwave cavities which include, but not limited to, developing high fidelity electromagnetic modeling, solving issues of cavity mode localization, construction techniques and materials, etc. In addition the ultra-low power expected from axion-to-photon conversions requires extraordinarily sensitive sensors. There have been rapid advances in superconducting quantum limited amplifier technology and this workshop will discuss Microstrip SQUIDs, JPAs, single photon counters and other possible detection methods. The workshop is intended to draw in subject matter experts from LLNL, SLAC, LBNL, Fermilab, U. of Washington, U. of Florida, U.C. Berkeley and others from around the world who are knowledgeable in axion searches, accelerator cavities and low temperature techniques and signal detection. This workshop will be used to introduce researchers to the unique requirements of designing microwave cavities for axion searches as well as to develop new cavity systems that can extend searches for axion masses into currently inaccessible ranges. Though the workshop focuses on cavities for axion searches the cavity designs could have other applications such as accelerators or quantum information research. This workshop is supported by LLNL, the U. of Washington, and through a generous contribution from the Heising-Simons Foundation.

Group Photo Axion_RF_Cavity_Workshop_2017_Photo.jpg

Tuesday, 10 January

1 Introduction & Welcome

In this talk I will discuss the motivation behind this workshop by introducing the dark matter axion and the haloscope technique to search for it. This technique uses microwave cavities to resonantly enhance the conversion rate of axions to potentially detectable levels. I will layout the number of design challenges facing experimental efforts moving forward.

Speaker: Dr Gianpaolo Carosi (Lawrence Livermore National Laboratory)

Slides Introduction_and_Overview_Jan_2016_final.pdf Introduction_and_Overview_Jan_2016_final.pptx

2 Introduction to RF-Structures and Their Design

The numerical design presentation addresses two topics: (1) Numerical Methods that include resonator design basics, introduction to Finite Difference, Finite Element and other methods, and (2) Introduction to Simulation Software that covers 2D and 3D software tools and their applicability, concepts for problem descriptions, interaction with particles, couplers, mechanical and thermal design, and finally a list of tips, tricks and challenges.

Speaker: Dr Frank Krawczyk (Los Alamos National Laboratory)

Slides Introduction_to_Rf-Structures-2017.pdf Introduction_to_Rf-Structures-2017.pptx

10:30 Coffee Break

3 Keysight - Back to basics

Slides B2B-Network-Analysis.pdf B2B_Spectrum_Analysis_Nov_2017.pdf

12:30 Lunch

4 Simulation of Superconducting QUBIT devices

Superconducting qubits have matured from platforms demonstrating and manipulating macroscopic coherent quantum states to realizing exotic quantum states, running surface error correction codes, and single photon detection to name a few recent milestones. This talk will review the fundamentals of circuit QED related to the design and simulation of superconducting qubits. A brief overview of how to simulate the classical components of these devices using the finite element multiphysics software, COMSOL, will follow the discussion of their equivalent circuit models.

Speaker: Nick Materise (Lawrence Livermore National Laboratory)

Slides materise_admx_comsol_qubits_170110.pdf materise_admx_comsol_qubits_170110.pptx

5 Symmetry Breaking in Haloscope Microwave Cavities

Axion haloscope detectors use microwave cavities permeated by a magnetic field to resonate photons converted from axions via the Primackoff effect. The sensitivity of a detector is proportional to the coupling of the cavity’s search mode to the axion conversion. Transverse symmetry breaking is used to tune the search modes for scanning across a range of axion masses. However, computer simulations show transverse and longitudinal symmetry breaking reduce mode-to-conversion coupling. Simulations also show longitudinal symmetry breaking leads to other undesired consequences like mode mixing and mode crowding. These results further complicate axion dark matter searches, requiring mode identification techniques. The effects of symmetry breaking on haloscope cavity modes will be presented along with mode identification techniques.

Speaker: Mr Ian Stern (University of Florida)

Slides Symmetry_Breaking_in_Microwave_Cavities.pdf

6 Application of the Bead-Perturbation Technique to a Study of a Tunable 5 GHz Annular Cavity

Microwave cavities for a Sikivie-type axion search are subject to several challenging constraints. In the fabrication and operation of such cavities, often used at frequencies where the resonator is highly overmoded, it is important to be able to reliably identify the symmetry of the mode of interest, confirm its form factor, and to determine the frequency ranges where mode crossings with intruder levels have caused unacceptable admixing of the purity of the mode of interest. A simple and powerful diagnostic for mapping out the electric field of a cavity is the bead perturbation technique. While a standard tool in accelerator physics, we have for the first time applied this technique to cavities used in the axion search. In this talk, I will report initial results from an extensive study for the initial cavity used in ADMX-HF. This is an annular resonator of 25.4 cm x 10.2 cm diameter, with an off-center 5.1 cm diameter pivoted copper tuning rod, for which the TM(010) mode could be tuned over the 3.4-5.8 GHz range. Two effects in particular have been investigated, i.e. the role of rod misalignment in mode localization, and mode-mixing at avoided crossings of TM and TE modes. These results are being brought together with precision metrology and high-fidelity simulations. This work was supported under the auspices of the National Science Foundation, under grant PHY-1306729, and the Heising-Simons Foundation under grant 2014-182.

Speaker: Nicholas Rapidis (University of California, Berkeley)

Slides RAPIDIS_secondary.pdf RAPIDIS_talk.pdf

15:15 Coffee Break

7 Ansys HFSS Tutorial

This informal session will provide an introductory tutorial on the use of Ansys High Frequency Structure Simulator (HFSS) with a live demonstration of example models. Specific features relevant to achieving accurate cavity and antenna simulation results will be highlighted.

Speaker: Mark Jones (Pacific Northwest National Laboratory)

Slides MJones_-_HFSS_Tutorial_for_Axion_Cavity_Workshop.pdf MJones_-_HFSS_Tutorial_for_Axion_Cavity_Workshop.pptx

8 Hands on with simulations and microwave hardware

Wednesday, 11 January

9 ABRACADABRA: A broadband/resonant search for axions

In the long-wavelength regime, axion interactions with a static magnetic field can be described in terms of an effective current which sources a small oscillating magnetic field. I will describe a new experiment (ABRACADABRA) to detect this axion effective current which can operate with either broadband or resonant readout of the signal. Inspired by advances in medical physics and precision magnetometry, the broadband approach has advantages at low axion mass and can probe many decades of mass simultaneously. The combination of broadband and resonant approaches potentially has sensitivity to GUT-scale QCD axions. I will discuss recent progress on a prototype of ABRACADABRA under development at MIT.

Speaker: Dr Yonatan Kahn (Princeton University)

Slides ABRACADABRA_Kahn.key ABRACADABRA_Kahn.pdf

10 DM Radio

Speaker: Dr Dale Li (SLAC National Accelerator Laboratory)

Slides Livermore_2017_Dale_Li.pdf Livermore_2017_Dale_Li.pptx

10:10 Coffee Break

11 Analysis of a Corrugated Coaxial Waveguide Resonator for Mode Rarefaction in a Gyrotron

---Canceled Talk--- In the development of high-power, high-frequency gyrotrons, two major constraints are the thermal loading of the wall of the waveguide resonator and the potential depression inhibiting the transport of large electron beam currents. The introduction of a coaxial metal insert in a circular waveguide resonator reduces the potential depression caused by the presence of the electron beam, and thus a coaxial waveguide transports a higher vacuum limiting current than a circular waveguide (without such a coaxial insert). The enhanced current transport capability of a gyrotron using a coaxial waveguide increases the electron beam power available in the device for conversion to microwaves. An unfolding method of selecting the desired mode amongst the competing nearby modes in a coaxial cavity interaction structure by tapering the structure cross section will be presented.

Speaker: Dr Kalpana Singh (University of Alberta)

12 Novel materials for dispersion engineering in an accelerator environment

This talk provides an introduction to novel materials for dispersion engineering in an accelerator environment. The focus will me on metamaterials, the unique effects they give rise to and how these can provide interesting responses in accelerators. An overview of existing metamaterials schemes for accelerator applications will be presented, including an in depth discussion on the CSRR (complementary split ring resonator) loaded waveguide for reverse Cherenkov applications. The challenges these materials pose in the accelerator environment will be discussed and methods to mitigate these effects proposed. In addition to metamaterials, wavelength scale dispersion engineering will be discussed in cases where the length scales of metamaterials are unsuitable. Finally, new plasmonic materials, such as transparent conducting oxides and intermetallics with be discussed and their integration into both metamaterial and dispersion engineering will be explored.

Speaker: Dr Emmy Sharples (Helmholtz Zentrum Berlin)

Slides EmmyPresentation.pdf EmmyPresentation.pptx

13 Novel Resonant Cavity Designs and Applications to Axion Haloscopes

At the University of Western Australia we are investigating novel resonant cavity structures for a variety of applications ranging from tests of fundamental physics, quantum information techniques and applied technologies. After a short introduction, this presentation will focus on our work in designing novel cavities geometries for axion detection. First we will discuss our work on using 3D lumped “re-entrant” cavities, which offer high tuning ranges at cryogenic temperatures [1], for the potential application for detection of low mass axions between the range of 50 neV to 1 μev [2]. Secondly, we will discuss work on using multiple post cavities [3-5] and how they may aid in designing high frequency haloscopes. Thirdly, we will present our experimental and theoretical work on higher order reentrant post modes, and discuss their sensitivity to axions as well as implications for cavities with tuning posts and gaps between the post and cavity end wall [6]. Finally we will discuss our work on dielectric cavities, 3D printed superconducting cavities [7] and some new designs for high frequency axion haloscopes. [1] NC Carvalho, Y Fan, ME Tobar, “Piezoelectric tunable microwave superconducting cavity”, Rev. Sci. Instrum., vol. 87, 094702, 2016. [2] BT McAllister, SR Parker, ME Tobar, “3D lumped LC resonators as low mass axion haloscopes”, Phys. Rev. D 94, 042001, 2016. [3] M Goryachev, ME Tobar, “Reconfigurable microwave photonic topological insulator,” accepted to be published in Phys. Rev. Applied, Nov. 2016. arXiv:1606.02001[physics.ins-det]. [4] M Goryachev, ME Tobar, Creating Tuneable Microwave Media from a 2D Lattice of Re-entrant Posts, Journal of Applied Physics, vol. 118, 204504, 2015. [5] M Goryachev, ME Tobar, “The 3D split-ring cavity lattice: a new metastructure for engineering arrays of coupled microwave harmonic oscillators,” New J. Phys. 17, 023003, 2015. [6] BT McAllister, Y Shen, SR Parker, ME. Tobar, “Higher Order Reentrant Post Modes in Cylindrical Cavities,” arXiv:1611.08939[physics.ins-det]. [7] DL Creedon, M Goryachev, N Kostylev, T Sercombe, ME Tobar, A 3D Printed Superconducting Aluminium Microwave Cavity, Appl. Phys. Lett. vol. 109 , 032601, 2016.

Speaker: Prof. Michael Tobar (University of Western Australia)

Slides AxionWS.pptx

12:25 Lunch

14 PBG cavities for future ADMX

As ADMX is looking towards higher frequencies, the reasons to use conventional microwave cavities over other technologies becomes less clear cut. In this talk I will discuss ideas using photonic bandgap structures and meta materials in conjunction with microwave cavities; the benefits which they present and the challenges they pose.

Speaker: Dr Nathan Woollett (LLNL)

Slides CavityWorkshop_Woollett.pdf CavityWorkshop_Woollett.pptx

15 The Electric Tiger Experiment: a Proof-of-Concept for the Periodic Dielectric Loaded Resonator

The Electric Tiger experiment is a resonant cavity for the detection of axions in the 4-5 GHz range. The cavity uses a first-of-its-kind detection method – dielectric media placed at regularly spaced intervals within the cavity. Such a search method allows for the construction of a simple tuning mechanism and a wide range of frequencies that can be searched with a single cavity. The tuning and mode identifications/tracking techniques developed by this experiment are translatable to open resonator axion searches that are suitable for very high frequency ranges ( > 10 GHz ).

Speaker: Benjamin Phillips (University of Washington)

Slides

• blurred_coupling_map_animation.gif
• coupling_map_animation.gif
• etig_llnl_presentation.pdf
• filtered_coupling_map_animation.gif
• mode_map_animation.gif

16 TE Mode Ridged Waveguide Cavities for ADMX Research

The talk will cover the application of Ridged waveguide cavities for ADMX research. Designs are given that cover the frequency ragne of 2 GHz to 20 GHz. Their Q's, Coupling Form Factor, and tolerances will be presented. These cavities resonate in the lowest order TE 100 mode because of their long length.

Speaker: Alfred Moretti (Fermilab)

Slides Moretti_TE_Mode_Ridged_Waveguide_Cavities_for_ADMX_Studies.pdf

17 Work on Superconducting Aluminum Cavities

Current efforts on studying aluminum superconducting cavities at Fermilab will be presented.

Speaker: Alfred Moretti (Fermilab)

Slides PureAlCav010817_Moretti.pdf PureAlCav010817_Moretti.pptx

18 Axion Haloscopes with Toroidal Geometry

The axion power in a resonant cavity is proportional to B^2V. The radius of cylindrical cavity decreases linearly with increasing frequency thus decreasing the volume as the square of the frequency increase. Attempting to recover the volume, and thus a reasonable axion power, one can increase the length of the cavity. This quickly leads to mode crossings and potential mode localizations due to fabrication errors. To address these issues we have decided to explore a toroidal geometry for an axion haloscope. The toroid dispenses with endcaps so the primary B field does not encounter any perpendicular surfaces, making it an attractive design for superconducting film application. In our first phase of R&D we have designed and fabricated a small, 140mm diameter, toroid and explored its resonant behavior with and without a tuning system. We have also installed a toroidal solenoid and taken data in the 25-33 µeV range. I will present our experiences with our “Cappuccino Sub” and some future plans.

Speaker: Dr Harry Themann (Center for Axion and Precision Physics)

Slides Toroidal_Axion_Haloscope_Development_at_CAPP_Rev_A.pdf

15:45 Coffee Break

19 Overview of SRF Cavity R&D at Jefferson Lab

A brief description of SRF cavity R&D activities at JLAB will be presented. For several decades, Jefferson Lab has been engaged in small sample studies of superconducting film properties using deposition by energetic ion condensation. Recently a program has been launched using this technique to energetically deposit films on copper cavity substrates for accelerator application, which will be discussed.

Speaker: Dr Larry Phillips (Jefferson National Lab)

Slides SRF_Research_at_Jefferson_Lab.pdf SRF_Research_at_Jefferson_Lab.pptx

20 Hybrid cavities for axion detectors

Hybrid cavities, cavities with a layer of superconductor applied on top of the OFHC copper cavity walls, are studied. The goal is to improve the quality factor (Q) of the resonator. The superconductor must have its surface parallel to the external field and must be thinner than the penetration depth and comparable in thickness to the fluxoid spacing in the type II superconductor at the 8 T operating field. Q for a single thin layer and of a multilayer superconductor/ insulator stack applied directly to the copper are estimated. The results for these thin-film coatings are not good. However, if a layer or a multilayer stack of the superconductor were separated from the copper by a thick insulating spacer, one that is about a quarter wavelength at the cavity resonant frequency, extremely high Q factors could be obtained. Even when the contribution of the normal metal ends (where the external field is perpendicular to the surface) is included, the Q is improved compared to an all-metal cavity.

Speaker: David Tanner (University of Florida)

Slides Hybrid-CavityWorkshop.pdf

21 Upper critical field of type 2 superconductor under vertical and parallel DC magnetic field.

For the successful measurement of cold dark matter, AXION, it is necessary for the development of the high Q superconducting radio frequency (RF) cavity working under high DC magnetic field. For it, type 2 superconducting materials with high critical field and high critical temperature have been suggested. Unlike type 1 superconducting materials, type 2 superconducting materials have the vortex state between the first and the second critical field, respectively, which is the first and the second order thermo dynamic transition. Therefore, it is needed to study the RF characteristics of type 2 superconducting materials in the vortex state. Before a magnetic field dependent RF study of type 2 superconducting materials, we study the upper critical field of alloy superconductor NbTi under vertical and parallel DC magnetic field using four probe measurement. Magnetic field dependent critical temperatures of NbTi film show the difference as the DC magnetic field direction applied on NbTi film. From the discrepancy between them, we report on the optimal conditions of type 2 superconducting film for the application on high Q superconducting RF cavity for AXION measurement.

Speaker: Dr Won-Jun Jang (Center for Axion and precision physics research center)

Slides Cavity_workshop_won-Jun_Jang.pdf Cavity_workshop_won-Jun_Jang.pptx

22 Discussion Session

Thursday, 12 January

23 First results from a microwave cavity axion search at 24 μeV

I will report on the first results from a new search for axion dark matter using a microwave cavity detector at ~5 GHz frequencies. This detector has achieved near-quantum-limited sensitivity using a dilution refrigerator and Josephson parametric amplifier, and excluded axion-photon-photon couplings a factor of 2.3 above the benchmark KSVZ model in the mass range 23.55 μeV< m <24.0 μeV. These are the first limits within the QCD axion model band in the mass decade above 10 μeV.

Speaker: Benjamin Brubaker (Yale University)

Slides LLNL_1_2017_brubaker.pdf

24 CULTASK: The first axion search experiment in Korea

CAPP’s axion searching experiment named as CULTASK (CAPP’s Ultra Low Temperature Axion Search in Korea) adopts P. Sikivies’s axion haloscope that uses strong magnetic field applied high Q factor of microwave cavity. We have started the first CULTASK experiment at 10.3μeV mass region and we demonstrate the progress and prospect. The dilution refrigerator (Bluefors LD 400 series) with 8T superconducting magnet is fully equipped and it successfully cools the cavity down to 30mK or less even with all the heavy supporting jigs and electronic components such as piezo actuators. We especially use vertically split cavity that promises to solve contact problem of TM010 mode in cylindrical cavity. The resonance frequency is tunable within 2.1GHz to 2.5GHz by perturbing the field with high permeability of dielectric rod; (CULTASK uses 99.99% sapphire), which is driven by a rotational piezo. The unloaded Q factor measurement is more than 50,000 when the cavity is in cryogenic condition. SQUID amplifier test results will be shown either, which would be used in next run.

Speaker: Dr Ohjoon Kwon (Center for axion and precision physics research @ Institute for Basic Science)

Slides 2017_cavity_workshop_Ohjoon_3.pptx 2017_cavity_workshop_Ohjoon_LLNL.pdf

10:10 Coffee Break

25 The Cosmic Axion Spin Precession Experiment (CASPEr)

The nature of dark matter is a key problem in modern physics, and it is important to develop techniques to search for a wide class of dark-matter candidates. Axions, originally introduced to resolve the strong CP problem in Quantum Chromodynamics (QCD), and axion-like particles (ALPs) are strongly motivated dark matter candidates. Nuclear spins interacting with a background axion/ALP field experience an energy shift which oscillates at a frequency equal to the axion/ALP Compton frequency. The Cosmic Axion Spin Precession Experiment (CASPEr) uses precision magnetometry and NMR techniques to search for the effects of this interaction. The experimental signature is precession of the nuclear spins under the condition of magnetic resonance: when the bias magnetic field is tuned such that the nuclear spin sublevel splitting is equal to the axion/ALP Compton frequency. These experiments have the potential to detect axion-like dark matter in a wide mass range (10^{-12} eV to 10^{-6} eV) and with coupling strengths many orders of magnitude beyond the current astrophysical and laboratory limits, and eventually all the way down to the QCD axion.

Speaker: Prof. Derek Kimball (California State University - East Bay)

Slides CASPEr-overview-Livermore-2017-Kimball.pdf CASPEr-overview-Livermore-2017-Kimball.pptx

26 The QUAX experiment

We present a proposal to search for QCD axions with mass in the 200 μeV range, assuming that they make a dominant component of dark matter. Due to the axion-electron spin coupling, their effect is equivalent to the application of an oscillating rf field with frequency and amplitude fixed by the axion mass and coupling respectively. This equivalent magnetic field would produce spin flips in a magnetic sample placed inside a static magnetic field, which determines the resonant interaction at the Larmor frequency. Spin flips would subsequently emit radio frequency photons that can be detected by a suitable quantum counter in an ultra-cryogenic environment. An updated report of the experimental results will be presented, together with a projection of future improvements to be tested.

Speaker: Dr Nicolò Crescini (Univesity of Padua)

Slides quax_llnl_nopause.pdf

27 Progress on the ARIADNE axion experiment

ARIADNE is a collaborative effort to search for the QCD axion using techniques based on nuclear magnetic resonance. In the experiment, axions or axion-like particles would mediate short-range spin-dependent interactions between a laser-polarized 3He gas and a rotating (unpolarized) tungsten attractor, acting as a tiny, fictitious “magnetic field”. The experiment has the potential to probe deep within the theoretically interesting regime for the QCD axion in the mass range of 0.1-10 meV, while being independent of cosmological assumptions. The experiment relies on a stable rotary mechanism and superconducting magnetic shielding, required to screen the 3He sample from ordinary magnetic noise. Progress on testing the stability of the rotary mechanism will be reported, and the design for the superconducting shielding in the experiment will be discussed.

Speaker: Prof. Andrew Geraci (University of Nevada Reno)

Slides Geraci_LLNL2_Jan2017.pdf Geraci_LLNL2_Jan2017.pptx

12:25 Lunch

28 Searching for Low Mass Axions with an LC Circuit

Axions are a promising cold dark matter candidate.  Using the conversion of axions to photons in the presence of a magnetic field haloscopes can be employed to detect axions as is done in microwave cavity searches such as ADMX.  To search for lighter, low frequency axions in the unexplored sub 100 neV (50 MHz) range a tunable LC circuit has been proposed. Progress in the development of such an LC circuit based search will be presented. This will include preliminary results from prototypes using electrical tuning, superconducting inductive loops, and aluminum shielding.

Speaker: Ms Nicole Crisosto (University of Florida ADMX)

Slides Crisosto_ADMX_Microwave_Cavity_Workshop_2017.pdf

29 Microstrip Squid Amplifiers for ADMX

Speaker: Mr Sean O'Kelley (UC Berkeley)

Slides S_OKELLEY_2017_Cavity_WorkshopTalk_v1.1.pdf

30 Josephson Parametric Amplifiers for Axion Searches

Measurement of weak signals consisting of few microwave photons requires multiple amplification stages for efficient detection by room temperature electronics. However, state-of-the-art commercially available microwave amplifiers add the equivalent of tens of photons of noise, making them insufficient for the amplification of single- or sub-photon signals. Interest in measuring photon-level signals from superconducting circuits has motivated the intensive development of Josephson parametric amplifiers (JPAs), which have become workhorses of the superconducting qubit field. The robustness and near quantum-limited noise performance of the JPA also make it an appealing candidate for detecting small microwave signals in axion-search experiments. In this talk, we present a brief introduction to JPAs along with an update on devices fabricated and characterized for ADMX.

Speaker: Mr Yanjie Qiu (Quantum Nanoelectronics Laboratory, University of California, Berkeley)

Slides Yanjie_Qiu_Presentation.pdf Yanjie_Qiu_Presentation.pptx

31 Detecting Axion Dark Matter with Superconducting Qubits

The Axion Dark Matter eXperiment (ADMX) aims to detect dark matter axions converting to single photons in a resonant cavity bathed in a uniform magnetic field. A qubit (two level system) operating as a single microwave photon detector is a viable readout system for ADMX and may offer advantages over the quantum limited amplifiers currently used. When weakly coupled to the detection cavity, the qubit transition frequency is shifted by an amount proportional to the cavity photon number. Through spectroscopy of the qubit, the frequency shift is measured and the cavity occupation number is extracted. At low enough temperatures, this would allow sensitivities exceeding that of the standard quantum limit.

Speaker: Akash Dixit (University of Chicago)

Slides qubit_cavity_A_Dixit_v2.pdf

15:45 Coffee Break

32 Multiple-cavity detector for axion search

Exploring higher frequency regions in axion dark matter searches using microwave cavity detectors requires a smaller size of the cavity as the TM010 frequency scales inversely with the cavity radius. One of the intuitive ways to make a maximal use of a given magnet volume, and thereby to increase the experimental sensitivity, is to bundle multiple cavities together and combine their individual outputs ensuring phase-matching of the coherent axion signal. The Experiment of Axion Search aT CAPP (EAST-C) is a dedicated project to develop multiple-cavity systems at the Centre for Axion and Precision Physics Research (CAPP) of the Institute for Basic Science (IBS). The conceptual design of the phase-matching mechanism and experimental feasibility using a double-cavity system will be presented in this talk.

Speaker: Dr SungWoo YOUN (CAPP/IBS)

Slides Cavity_Workshop_2017_YOUN.pdf Cavity_Workshop_2017_YOUN.pptx

33 Multi Cavity Array for Axion Dark Matter Experiment

The current version of ADMX (Axion Dark Matter Experiment) utilizes a single 1 meter long by 0.5 meter diameter RF cavity to search for axion to photon decay with resonance frequencies ranging from ~580 to 890 MHz. We investigate the use of the current ADMX experimental space for the detection of axion decay in the range of 1.0 to 2.0 GHz. In order to maximize the detector volume available we propose an array of 4 or 8 mode-locked RF cavities with 15cm diameters to replace the current single cavity detector. In our design we propose a single rotor tuning rod array which minimizes gaps as well as differences in rod motion within the cavities. Utilizing cavities of different lengths we are able to reduce the effects of critical mode crossings.

Speaker: joseph gleason (UF)

Slides ADMX_RF_Gleason.pdf

34 Pound – Drever – Hall frequency locking method

We use the Pound reflection locking method to tune the cavity. We input a phase-modulated RF signal to the cavity through a directional coupler. The RF signal reflected by the cavity is given to a lock in amplifier using a Zero bias Schottky detector. The output of the lock in amplifier gives a measure of how far the carrier is off the resonance. This output is fed to an integrator and the signal can be used as a feedback signal to tune the cavity using a servo control.

Speaker: Shriram Sadashivajois (University of Florida)

Slides Axion_PDH_locking_Ram_final.pdf

35 Open Discussion

18:30 Workshop Dinner

The Workshop Dinner will take place at Uncle Yu's restaurant in downtown Livermore.

Friday, 13 January

36 Evaluation of Commercial Phase Shifters for Cryogenic Applications

Details of our work on evaluating commercial phase shifters for cavity impedance matching at cryogenic temperatures are presented. A brief overview of the circuitry is given followed by information on two candidate phase shifters – one surface mount and one packaged. The test and modelling procedures for both bench and cryogenic measurements are outlined. Initial cryogenic measurements indicated no variation in phase with bias voltage – this problem was traced to the use silicon varactors in these commercial units. The circuit topologies were studied and GaAs varactor replacements are being ordered.

Speaker: Dr Richard Bradley (NRAO NTC)

Slides Bradley_PS_Eval.pdf

37 Electronic tuning with dielectrics

Axion searches above ~1 GHz will employ multiple resonators locked to the same frequency. Fine tuning of individual resonators may be accomplished using thin films of strontium titanate (STO) and related materials, whose dielectic strength can be varied through DC voltage bias. We have developed a method to evaluate these films using coplanar waveguide resonators. We will discuss the asssessment of the resonator system and films at room temperature and at cryogenic temperatures.

Speaker: Daniel Bowring (Fermilab)

Slides Bowring-1-2017.pdf

38 Active circuits for resonant axion detectors

The key difficulty taking cavity axion detectors forward is the rate of coverage of possible axion masses. With metal cavity boundary conditions determining the modal frequencies, you are limited to the physical modes of the cavity having a high form factor. We examine whether artificial modes generated by feedback through high Q resonant filters outside the cavity could form artificial high-Q modes. Running many of these filters in parallel could generate a picket fence of modes, which might for some configurations allow one to multiply the search rate by the number of these artificial modes. We examine the practicalities of implementing these external resonators including their noise contribution and the question of their behaviour in the quantum limit.

Speaker: Dr Ian Bailey (Lancaster University / Cockcroft Institute of Accelerator Science and Technology)

Slides ActiveResonator_IRB130117.pdf

10:30 Coffee Break

39 The ORGAN Experiment

The Frequency and Quantum Metrology Laboratory at UWA is in the process of constructing a haloscope (the Oscillating Resonant Group Axion converter, or ORGAN) designed initially to search for axions around 110 micro-eV, or 26.6 GHz, with the ultimate goal of performing a wide range search above 20 GHz. The primary motivation for this search is a direct test of the Beck result [1], which claims a potential signal due to an axion resonance effect in Josephson Junctions. The proposed signal suggests axions at 26.6 GHz +/- ~500 MHz. The search will consist of several phases, and the initial pathfinding run is currently underway. The pathfinding search consists of a single copper resonant cavity embedded in a 7 T magnetic field at 4 K, employing a traditional HEMT based amplifier and readout via a high-speed digitizer, the detecting mode was chosen to be a TM¬020 mode [2]. We discuss the preparations for this search, as well as the planned future phases and extensions, which includes first results at cryogenic temperatures. We are exploring different mechanisms of cavity tuning, as well as different methods for the power combining and synchronisation of multiple cavities, a common theme in high frequency axion searches. We will discuss novel cross-correlation measurement schemes, which are two channel measurements where signals common between channels are preserved, whilst noise uncommon between channels is rejected. We propose a way to utilize these techniques in multiple cavity axion searches [3]. [1] C. Beck, Phys. Rev. Lett. 111, 231801 (2013) doi:10.1103/PhysRevLett.111.231801 [arXiv:1309.3790 [hep-ph]]. [2] B. T. McAllister, S. R. Parker, E. N. Ivanov, and M. E. Tobar, Proceedings of the 12th Patras Workshop on Axions, WIMPs and WISPs [arXiv:1611.08082 [hep-ex]]. [3] S. R. Parker, B. McAllister, E. N. Ivanov and M. E. Tobar, arXiv:1510.05775 [physics.ins-det]. (update forthcoming)

Speaker: Mr Ben McAllister (ARC Centre of Excellence for Engineered Quantum Systems, School of Physics, University of Western Australia)

Slides CavityConference2017_Mcallister.pdf

40 First test of a photonic band gap structure for ADMX-HF

Haloscopic axion searches require the tuning of a TM mode in a microwave cavity. Traditional cavities contain many unwanted modes which can result in mode crossings, ultimately reducing the effective tuning range of a cavity and slowing scan rates. Photonic band gap (PBG) structures have the potential to create resonators without TE modes, allowing for uninterrupted tuning. A tunable PBG structure has been designed for ADMX-HF. A prototype has been built and tested to validate simulations. Results of the fixed frequency case will be shown as well as details of the expected tuning. This work was supported under the auspices of the National Science Foundation, under grants PHY-1067242 and PHY-1306729and the Heising-Simons Foundation under grant 2014-182.

Speaker: Samantha Lewis (University of California - Berkeley)

Slides Lewis2017.pdf

41 Workshop Closeout

Speaker: Dr Gianpaolo Carosi (Lawrence Livermore National Laboratory)

12:30 Lunch