Screening currents increase thermal quench propagation speed in ultra-high-field REBCO magnets

Abstract: Superconducting REBCO ($RE$Ba$2$Cu$_3$O${7-x}$, where $RE$ is a rare earth, typically Y, Gd or Eu) electromagnets are useful for many applications like medical magnetic resonace imaging (MRI), nuclear magnetic resonance (NMR) spectroscopy, and magnets for particle accelerators and detectors. REBCO magnets are also the core of many nuclear fusion energy start-ups. In order to avoid permanent damage during operation, magnet design needs to take electro-thermal quench into account, which is due to unavoidable REBCO tape or magnet imperfections. However, most high-field magnet designs do not take superconducting screening currents into account. In this work, we show that it is essential to consider screening currents in magnet design, since they highly speed-up electrothermal quench propagation. Our study is based on detailed numerical modeling, based on the Minimum Electromagnetic Entropy Production (MEMEP) and Finite Differences (MEMEP-FD). Benchmarking with well-established Partial Element Equivalent Circuit (PEEC) model supports the correctness of MEMEP-FD. This work focusses on a 32 T all-superconducting magnet design and we analyze in detail the time evolution of electrothermal quench. Our findings will have an impact in the design of ultra-high-field magnets for NMR or user facilities, and possibly for other kinds of magnets, like those for fusion energy.