Numerical study of the effect of anisotropy and field dependence of critical current on AC loss in REBCO coated conductors and stacks

Abstract

High-temperature superconducting (HTS) AC electrical devices generally carry AC transport currents and are exposed to AC external magnetic fields with arbitrary orientations. Realistic HTS coated conductors (CCs) show diverse critical current anisotropy and field dependence (I_c(B,$\theta$)), which directly affect the superconducting behavior. However, under complex electromagnetic (EM) conditions, the discrepancies in AC loss characteristics caused by different I_c(B,$\theta$) features are still unclear. Moreover, the selection of CCs with desirable I_c(B,$\theta$) features to further reduce AC loss under various EM conditions remains overlooked. In this work, the transport AC loss (Q_t) (without field), magnetization loss (Q_m), and total AC loss (Q_tot) of the nearly isotropic Shanghai Creative (SCST) CC and the strongly anisotropic Fujikura (FYSC) CC, along with their stacks, are investigated in the range of 90° and 90° (parallel to the CC wide surface) field angles based on the H-formulation. The results show that, due to the opposite angular dependence of I_c, the effective penetration fields of these two CCs or stacks exhibit distinct trends with the field angle, and the Q_m in the nearly isotropic CC is less dominated by the perpendicular field component compared to that in the strongly anisotropic CC. Furthermore, due to the different field dependence of I_c at various field angles, the two CCs or stacks exhibit opposite flux flow loss behaviors with the field angle. Overall, the SCST CC and its stack show lower Q_tot within the angle range around 0°, and this range expands as the external field increases, while the FYSC CC and its stack show lower Q_tot at the remaining angles. This is further explained by analyzing the field distribution and Q_tot of each tape in the stacks. This paper clarifies the discrepancies in AC loss caused by different I_c(B,$\theta$) and identifies the applicable EM conditions for different REBCO materials to reduce AC loss, providing valuable references for material selection to minimize loss in HTS AC devices across different scenarios.