Anisotropic in-plane field angle dependence of critical current in commercial REBCO tapes and its impact on toroidal field magnet for compact tokamak fusion device

The critical current (I_c) of commercial rare-earth barium copper oxide (REBCO) tapes is generally assumed to exhibit isotropic behavior with respect to the magnetic field angle applied within the tape’s basal plane (in-plane). This paper investigates the field angle dependence of critical current, both in-plane and out-of-plane, for commercial REBCO tapes manufactured by SuperOX, under fields ranging from 0 T to 8 T at 20 K. Remarkably, the in-plane field angle dependence of I_c shows significant anisotropy, with the minimum I_c no longer occurring at the traditional 90° (parallel to the ab-plane), but instead shifting to approximately 130°, a phenomenon reported for the first time. This novel anisotropic in-plane field angle dependence of I_c can substantially affect the performance of toroidal field magnets for compact tokamak fusion devices. Simulations indicate that considering versus neglecting the anisotropic in-plane field angle dependence of I_c can lead to I_c variations of up to 19.58% within the D-shaped coils of the toroidal field magnets. The locations of maximum deviation vary across different double-pancake coils within the D-shaped winding packs. This study highlights the complexity of I_c distribution in toroidal field magnets for compact fusion applications, urging further consideration of anisotropic in-plane field angle dependence of I_c of commercial REBCO tapes in fusion magnet design.