Numerical study of quench in a HTS superconducting magnet for the 40T NHMFL project

The National High Magnetic Field Laboratory (NHMFL), USA, is advancing the development of a 40 T superconducting magnet, combining high-temperature REBCO inner coils with low-temperature superconducting (LTS) outer coils. As part of this initiative, a full-scale prototype coil—designated as the “Large Scale Coil” (LSC) has been fabricated and experimentally tested at 4.2 K using quench protection heaters. This thesis presents a comprehensive electrothermal numerical study of the LSC quench behaviour, performed using a coupled finite element method (FEM) model developed at the Department of Electrical, Electronics and Information Engineering (DEI), University of Bologna. The model incorporates homogenization of REBCO tapes and coil materials to reduce computational load while accurately coupling distributed contact resistances across the coil’s pancake submodules. Critical to this approach is the dynamic integration of temperature and field-dependent material properties, achieved through custom C-code subroutines linked to COMSOL Multiphysics simulations. Comparative analysis between simulation results and experimental data reveals a rather good agreement in current decay, voltage rise, and resistive transitions across magnet modules. Notably, the study highlights the disproportionate quench sensitivity of modules 2 to 6; not necessarily the central, highest-field modules; due to combined magnetic field strength and field angle effects on the critical current. Further tests are ongoing on the LSC, and the model will be applied to eventually predict and interpret the experimental results. This work provides a useful tool to guide the design of next prototypes in the frame of 40 T magnet project.