Experimental study of high-temperature superconductor damage mechanisms from fast failure scenarios in high energy hadron colliders

The discovery of the Higgs boson by the ATLAS and CMS experiments at CERN from proton-proton collisions produced by the Large Hadron Collider (LHC) completed the experimental validation of the so-called "Standard Model" (SM). However, experimental observations require the Standard Model to be extended and future facilities aim at discovering Beyond Standard Model (BSM) mechanisms. The Future Circular Collider at CERN (FCC-hh) is such a proposed infrastructure which would push forward the "energy frontier" by an order of magnitude by colliding proton beams at centre-of-mass energy of 100 TeV and provide a state-of-art high-energy physics instrument until the end of the century. Such a collider will require novel superconducting magnets. The use of high-temperature superconductors (HTS) is considered in order to provide centre-of-mass energies even beyond 100 TeV and to achieve energy efficiency goals. Magnets based onNb3Sn coils featuring HTS inserts are being considered to achieve magnetic fields in excess of 16 T. Research and development is a key element to the widespread use of HTS conducting tapes based on Rare-earth Barium Copper Oxide (ReBCO). In parallel with the technological challenges posed by the development of high-field magnets, future colliders will also face tremendous challenges due to the stored beam energy, as the loss of only a minute fraction of the beam can cause damage to the machine components, and in particular to the superconducting materials. Dedicated machine protection systems must therefore be devised to prevent such accidents. At this stage, however, the damage limits of the novel superconducting materials considered for FCC-hh are still unknown and represent an essential information for the viability of the machine operation. This thesis is dedicated to the experimental characterisation of the so-called "damage limits", i.e. the limits in terms of energy density deposition beyond which the superconducting material would be permanently damaged. The experimental procedure follows the one of the experiments which were carried out to devise the damage limits of superconducting materials used at the Large Hadron Collider (LHC), namely Nb-Ti, and at the High-Luminosity Large Hadron Collider (HL-LHC), namely Nb3Sn. Samples of superconducting materials, including HTS tapes, were impacted at cryogenic temperatures with 440 GeV proton beams at the "High-Radiation to Materials" (HiRadMat) facility, a dedicated test facility which is part of the CERN Accelerator Complex. This beam impact experiment aims at reproducing the conditions of a typical fast failure scenario involving beam losses in the magnet apertures. The damage limits are drawn from the correlation between the energy deposited during the beam impact experiment and the difference in critical current density pre- and post-irradiation. In addition, to probe energy density deposition over longer time-scales, another experiment was carried out at room temperature where a current from a capacitive discharge in the HTS conductor was used to induce a fast temperature increase. This thesis analyses in detail the results obtained for the HTS tapes. To determine the amount of energy deposited in the samples during these experiments, new numerical simulations are performed using input parameter values measured during the experiment. For the beam-impact experiment, Geant4-based Monte Carlo simulations are performed using Beam Delivery Simulation (BDSIM). For the current discharge experiment, a detailed study of the experiment is provided. The presented model is developed to determine the fraction of the generated heat which caused the tape damage. The results on the energy density deposited in the tapes based on the best experimental model are presented and discussed in detail. The damage limits are then derived based on critical current measurements performed by collaborators at the University of Geneva. This study of the correlation between the samples damage level and their critical current degradation draws first conclusions on the damage limits of ReBCO tapes. This thesis features for the first time a complete analysis of the damage limits of HTS sample tapes based on the unique experimental campaign performed at CERN.