Electromagnetic-mechanical Simulation of High-field Test Coils and Conductor Degradation

The screening-current-induced stresses are raising growing concerns for the mechanical robustness of REBCO high-field magnets, particularly following the ‘Little Big Coil’ (LBC) experiments, which set a record field of 45.5T. In this paper, we examine the electromagnetic-mechanical behaviors of a set of single-pancake coils, which were originally designed as follow-up studies of the LBCs and tested in ultra-high fields without quench. A comparative study of the sequential model and the coupled model is carried out, demonstrating the perpendicular field modification due to conductor deformation and its effects on current and strain distributions. Local conductor degradation is taken into account by applying a stress/strain-dependent critical current profile while assuming linear elasticity. Under these assumptions, it is found that the suppressed strain response can lead to underestimation of conductor damage when using the strain-dependency, whilst conductor degradation is more sensitive to stress, yielding a conservative estimate on critical currents.