Numerical Analysis of the Reduction of Screening-Current-Induced Magnetic Field in Copper-Plated and Striated REBCO-Coated Conductor Wound into Pancake Coils

We aim to develop REBCO coil systems for high-magnetic-field whole-body magnetic resonance imaging and medical cyclotron for cancer therapy. These applications require high temporal stability and spatial uniformity of the generated magnetic field. Although the magnetic field generated during excitation changes very slowly, a screening-current-induced magnetic field (SCIF) is generated, which affects the required accuracy of the magnetic field. To reduce the SCIF, we focus on two methods: 1) a current control method, and 2) the use of striated coated conductors. When adopting a striated coated conductor, it is necessary to plate copper onto it in order to maintain its thermal stability and mechanical strength. However, in the copper-plated layer, changes in the magnetic field induce a coupling current, which flows between the filaments of the REBCO coated conductor. In this study, we apply the overshoot method with a plateau as a current control to eliminate the effect of coupling currents in the copper plating layer. We numerically analyzed the effectiveness of this overshoot method by visualizing the changes in the current distributions in a model pancake coil wound with a REBCO-coated conductor separated into two filaments. For that purpose, we used a three-dimensional nonlinear transient electromagnetic field computation in which the spiral arrangement of the pancake coil windings is appropriately considered.