Screening Current-Induced Stress in Edge-Impregnated REBCO Coils for 33T-CSM

Edge impregnation is a key technology for fabricating robust, high-field REBCO insert magnets. However, the effect of screening current-induced stress (SCIS), a critical challenge in ultra-high field magnet design, has not been fully clarified. This study aims to investigate the influence of SCIS on edge-impregnated REBCO coils through an electromagnetic-mechanical analysis. The investigation focuses on the 33 T cryogen-free superconducting magnet (33T-CSM) under development at HFLSM, Tohoku University. The analysis revealed that SCIS significantly amplified the hoop strain in edge-impregnated coils, predicting a maximum strain exceeding the conductor's irreversible limit. Compared with the full impregnation, the edge impregnation was insufficient to suppress SCIS to the acceptable level even with mechanical reinforcement although it made the delamination stress negligible. Notably, the analysis overestimated the hoop strain compared with experiments because the large-scale prototype coil (33T-LPC) has been successfully validated without degradation. Possible origins for the overestimation are discussed, including interfacial friction between the stacked pancake coils.