Repository for ASC 2022 abstracts, papers, slides and posters regarding MQXF magnets
Stefano Sgobba*1, Gonzalo Arnau Izquierdo1, Ignacio Aviles Santillana1, Bartosz Bulat2, Mickael Crouvizier1, Arnaud Devred1, Susana Izquierdo Bermudez1, Attilio Milanese1, Alice Moros1, Frederic Savary1, Ezio Todesco1
1European Organization for Nuclear Research, Geneve, Genève, Switzerland; 2FOSELEV Suisse SA, Geneva, Switzerland
Abstract: The future of particle accelerators is inevitably and strongly linked to the development of high – field magnets that enable higher energies and higher luminosity to be attained. The European Organization for Nuclear Research (CERN) is currently developing several Nb3Sn-based magnets for the High-Luminosity upgrade of the Large Hadron Collider (HL-LHC), in order to fully exploit its potential and surpass the intrinsic performance limitations of NbTi based magnets. The fabrication of Nb3Sn magnets is a challenging process as it requires to manage the brittleness and strain sensitivity of the conductors once they have undergone the reaction heat treatment to generate the superconducting Nb3Sn phase (A15). Accelerator magnet coils are usually manufactured following the wind-react-and-impregnate fabrication approach. This reduces the difficulty of working with brittle compounds, but adds uncertainties associated to volume change during phase transition for the formation of Nb3Sn and thermal expansion / contraction differentials of all the magnets’ components. In order to investigate the root causes of performance limitation or degradation observed on present magnets, several HL-LHC dipole and quadrupole magnet coils have been examined. The present paper illustrates an innovative methodology of investigations of the root causes at several fabrication stages and after cooldown and powering. Internal shear and bending loads on unsupported superconducting wires, which can cause their dislocation as well as cracks in the aggregates of Nb3Sn filaments, are suspected to be the main cause of limitation or degradation. The approach is based on a sequence of mesoscale observations of whole coil sections through non-destructive testing by an innovative high energy linac X-ray Computed Tomography (CT) technique, followed by materialographic assessment of internal events, geometrical distortions, and potential flaws using Light Optical Microscopy (LOM). Additionally, Scanning Electron Microscopy (SEM) and Focussed Ion Beam (FIB) were used to analyze strands or sub elements’ damage at particular localized positions as well as failure modes. This comprehensive approach provided an in-depth view of the examined coils by identifying and characterizing atypical features and imperfections in both the superconducting phase of the strands and the glass fibre/resin system, and univocally associate the quenches experienced by the coils to identified physical events, under the form of broken superconductive filaments or damaged strands. The results on Nb3Sn accelerator magnet coils are compared and put in perspective with similar observations carried out a decade ago on the Cable-in-Conduit Conductors for the ITER project.
Amalia Ballarino*1
1CERN, Geneva, Switzerland
Abstract: In order to increase the collisions rate in the Large Hadron Collider (LHC) by a factor ten during operation from 2029 to 2039, the LHC High Luminosity upgrade will rely on high-field, large aperture, Nb3Sn quadrupoles reaching peak fields in the conductor of ~ 12 T. For the first time, after more than a decade of development, the Nb3Sn will therefore become an enabling technology for accelerators, overcoming the intrinsic field limitations of Nb-Ti (~ 10 T) and nourishing hope for future high-energy machines requiring higher field (~ 16 T) magnets.
After a short overview on the progress of Nb3Sn procurement and qualification for HL-LHC, key potential performance limitations of state-of-the-art Nb3Sn conductor in magnets are analyzed. Lessons learnt from HL-LHC are presented. Requirements for future use of Nb3Sn high field accelerator magnets are discussed together with a roadmap that could drive conductor development toward satisfying the needs of future machines.