Role of asymmetric critical current on magnetization loss characteristics of (RE)Ba2Cu3O7−d coated conductors at various temperatures

Abstract

Commercial high-Tc superconducting (HTS) coated conductors exhibit asymmetric Ic(B,θ) characteristics, where B presents a DC magnetic field and θ is defined as the angle between an applied magnetic field and the normal component of the superconductor plane. The asymmetric Ic(B,θ) characteristics have a non-trivial influence on the dominant loss component, magnetization loss, of various HTS applications where HTS conductors are exposed to an AC magnetic field. Here, we present measurements of Ic(B,θ) and magnetization loss in a 12 mm-wide (Rare Earth)Ba2Cu3O7−d (REBCO) commercial coated conductor at 77, 70, and 65 K. In the Ic(B,θ) measurement, θ was varied around a full 360° revolution and B was varied up to 0.2 T. In terms of the magnetization loss measurement, the applied AC magnetic field amplitude is up to 110 mT and the field angle varied from 0° to 180°. At the three given temperatures, we observed magnetization loss variations among the field-angle range, in particular, for θ and 180°-θ, which are in mirror symmetry relative to the superconducting plane. Furthermore, this asymmetric field-angle dependence of the magnetization loss becomes more apparent at higher applied field amplitudes and lower operating temperatures. A finite element method simulation using H-formulation was carried out by directly interpolating the measured Ic(B,θ) data, and the simulation results reproduce the trend of the experimental results. We also found that the magnetization loss is not equivalent within the positive and negative half field cycles due to the asymmetric Ic(B,θ) characteristics of the conductor. Numerical simulations revealed a clear correlation between the magnetization loss and the asymmetric Ic(B,θ) data for the whole 360° field-angle range in the REBCO conductor. The asymmetry in the Ic(B,θ) data about the ab-peak causes differences in magnetization loss values for the mirror-symmetric field angles. The asymmetry in the Ic(B,θ) data upon field reversal also results in differences between magnetization loss values for the positive and negative cycles.