Numerical Simulations on AC Loss of the REBCO Tape Under Rotating Magnetic Field

REBCO coated conductors are exposed to rotating magnetic fields in various high-temperature superconducting (HTS) applications, such as HTS rotating machines and flux pumps. AC loss will be generated in the conductors when they carry AC current under rotating magnetic fields. We define AC loss in the coated conductors with and without current as total AC loss and magnetization loss, respectively. In this work, total AC loss and magnetization loss, in a REBCO tape under rotating magnetic fields and a perpendicular AC standing wave magnetic field are numerically investigated. We employ a 2D finite element method (FEM) based on the ${T} - {A}$ formulation, where ${T}$ and ${A}$ , are the current and magnetic vector potentials, respectively. In the simulations, the external magnetic field amplitude ( $B_{\mathrm {m}}$ ) is up to 500 mT and the reduced AC current ( $i$ = $I_{\mathrm {t}}/I_{\mathrm {c0}}$ ) varies from 0.1 to 0.9, where the $I_{\mathrm {t}}$ and $I_{\mathrm {c0}}$ are the amplitude of the transport current and self-field critical current of the conductor, respectively. Two different types of rotating fields are considered: one is a uniform field with equal amplitudes and phases at each position, and the other being a non-uniform field created by a rotating Halbach array. Different tape widths ranging from 4 mm to 40 mm are considered. Interestingly, the simulation results show substantially higher magnetization loss in the perpendicular standing wave compared to the rotating magnetic fields when $B_{\mathrm {m}}$ is over 100 mT. We attribute the result to the fact that the magnetization loss is propotional to $J_{\mathrm {c}}$ of the conductor at magnetic field amplitudes much greater than the effective penetration magnetic field. Evidently, the instantaneous loss curves of the SW model and RMF-Uniform model at 200 mT exhibited close similarity with evolving $J_{\mathrm {c}}$ values of the two models. Furthermore, when $B_{\mathrm {m}}$ is lower than the effective penetrated field, we observe a pronounced disparity in magnetization loss of the wider tape between uniform and non-uniform rotating fields. This highlights the importance of considering the effects of non-uniform field distribution, particularly at lower magnetic field. We further show that total AC loss under the perpendicular standing wave magnetic field remains greater than that under rotating magnetic fields when $B_{\mathrm {m}} > $ 100 mT and $i < 0.5$.