Damage Study on Single Strand Nb3Sn Ultra-Fast Beam Impact in Cryogenic Environment Simulation with Finite Element Method

At present, high energy physics requires high field magnets in large accelerators like CERN’s LHC. In addition to the existing Nb-Ti magnets the upcoming HL-LHC will use Nb$_{3}$Sn based magnets for the first time in a high energy accelerator. In specific failure cases, beams can impact the aperture of their accelerator. This causes ultra-fast local temperature gradients of several 100 K mm$^{−1}$ in the superconducting magnets. The thermal stresses associated with such impacts can potentially damage the superconductors. The scope of this study is to evaluate the superconductor damage limits in case of ultra fast, direct beam impact. To imitate the conditions in the accelerator an experiment was conducted at CERN’s HiRadMat beam irradiation facility. The strands were cooled to 4 K and consequently impacted by 3 × 10$^{12}$ 440 GeV protons over 600 ns. This thesis discusses the simulation model of the experiment. The model was set up with finite element software to improve the understanding of the observed degradation of critical parameters in Nb3Sn strands. The main damage mechanisms were identified to be residual lattice strain in the superconducting phase, and filament cracking. Following a brief overview of the impact experiment, the FEM simulation is described. Consequently, the implementation of the identified damage mechanisms in the post processing of the simulation data is explained. Lastly, the resulting superconductor properties are compared to post impact measurements. The comparison shows good agreement within the respective confidence intervals.