Numerical Evaluation of Reinforcement Structure Against Electromagnetic and Thermal Stresses in Stacked REBCO Pancake Coils

In recent years, high field REBCO coils have been applied with great interest to NMR and accelerators due to their high thermal stability and high current density. However, deteriorations and damages of REBCO coils are occurring. During the charge and discharge of REBCO coils, screening currents are induced to circulate in the windings, resulting in a non-uniform current distribution in the wires. It has been reported that the electromagnetic force distribution in the wire becomes significantly non-uniform, resulting in degradation of REBCO coils. In this study, the effects of stress and deformation of REBCO coils were investigated through electromagnetic stress analysis using two-dimensional axisymmetric structural analyses, taking into account thermal stress during cooling, tension during winding and electromagnetic force during not only charge and but also discharge, and the suppression of stress and deformation by the currently devised YOROI-coil (Y-based oxide superconductor and reinforcing outer integrated coil) structure and over-banding was evaluated.