Simplified Calculation Method of Screening-Current-Induced Magnetic Field for Optimal Shape Design of Compact REBCO Magnets

We have studied the optimal shape design of compact REBCO magnets using a distributed genetic algorithm (DGA). The proposed optimization method is very useful for shape design of compact MRI or NMR magnets. In REBCO magnets, a screening-current-induced magnetic field (SCMF) occurs due to the shape of the tape, and the negative effects of this SCMF become much more pronounced as the coil size becomes smaller. In general, the SCMF of REBCO magnets can be accurately calculated using a 2D or 3D finite element method (FEM). However, it is difficult to combine the FEM calculation with the DGA method. Therefore, it is necessary to propose a method for calculating the SCMF of REBCO magnets applicable to the DGA method. In this study, we propose a simplified calculation method for the SCMF of REBCO magnets based on an electric circuit model that can be applied to the DGA method. In the proposed simplified calculation method, the pancake-shaped REBCO coil is converted into a circular sheet with each turn, and the screening current induced in the coil is calculated by considering the self-inductance and mutual inductance of each sheet. In the width of the REBCO wire is also divided into multiple equivalent electrical circuits. Although the SCMF values ​​obtained by the proposed simplified calculation method did not completely match the results calculated by FEM, the calculation accuracy was sufficient to design the basic shape of a compact REBCO magnet taking into account the effects of the magnetic field due to the screening current.