Numerical Evaluation of Screening Current-Induced Magnetic Field in 1/2-Scale No-Insulation REBCO Coil System of Skeleton Cyclotron for Cancer Therapy

A new-generation accelerator named “skeleton cyclotron” is being developed for the stable production of 211At used for targeted alpha-particle therapy, which is expected to be effective in treating advanced cancer. The coil system for skeleton cyclotron consists of two types of air-core no-insulation (NI) REBCO coils: a circular main coil and a noncircular sector coil. To investigate the electromagnetic, thermal, and mechanical characteristics, we fabricated the ultra-baby skeleton cyclotron (UBSC) coil system, which is a 1/2-scale demonstration model of the NI-REBCO coil system. In NI-REBCO coils, the current flows in the radial direction, causing an excitation delay. Because this affects the magnetic field, it is necessary to perform screening current-induced magnetic field (SCIF) analysis that considers the current flowing in the radial direction in NI coil winding. Therefore, we developed a new simple calculation method for the SCIF using only electric circuits. In this study, we evaluated the electromagnetic behavior of 1/2-scale NI-REBCO coil system for UBSC by using the newly developed calculation method based on electrical circuit and confirmed its validity through comparison with experimental results.