Numerical analysis of electromagnetic behavior in D-shaped coils for toroidal field magnet

In the current emerging research of compact tokamak devices, it is important to study the electromagnetic response of D-shaped coils in the toroidal field (TF) magnet. In this paper, a numerical electromagnetic analysis of D-shaped coils for TF magnets in a fusion system is conducted, which focuses on no-insulation (NI) configuration. Utilizing a 3D finite element model with H-formulation, the electromagnetic behavior of the coil is investigated under varying charging rates, contact resistivity, and sudden discharge scenarios. The results reveal that NI coils exhibit significant charging delay effects due to radial current redistribution, with delay characteristics dependent on the charging rate and contact resistivity. AC loss analyses reveal that contact losses dominate at low contact resistance, while superconducting losses become negligible. The mutual inductance effects are also explored in nested D-shaped coil systems, showing that outer coil suddenly discharges induce transient perturbations in the internal coil, thereby threatening system stability. Furthermore, the electromagnetic characteristics of the complete TF magnet system are analyzed. These findings provide insights into optimizing TF magnet designs for compact tokamaks.