Electromagnetic design of a hybrid central solenoid for a medium-sized tokamak

The electromagnetic design optimization of a hybrid central solenoid (CS) coil is studied for a medium-sized superconducting fusion tokamak, which is smaller than the China Fusion Engineering Test Reactor and aims to realize a fusion power gain Q > 1. The CS coil uses ReBCO and Nb3Sn conductors in the high and low field sub-coils, which are both composed of six vertically stacked modules with unequal heights. Based on the medium-sized tokamak device, a code is written to maximize the magnetic flux, meanwhile constraining the peak fields, WP height, and the total conductor length. An optimization design of the hybrid CS coil is obtained using the code. Then, the electromagnetic field at initial energization (t = 0 s) and fast discharge is calculated using Maxwell and MATLAB, respectively. The operating current exhibits exponential decay to zero during fast discharge, with the current decrease rates of the high-temperature superconductivity and low-temperature superconductivity sub-coils determined by their inductances. The Maxwell electromagnetic analysis shows good agreement with the results of the self-written code. In addition, a 2D axisymmetric finite element model, incorporating cables, conductor jackets, and insulation, is developed and simulated using ANSYS’s coupled structural–thermal–electromagnetic solver.