Preliminary mechanical analysis of the CS coil design for a medium-sized tokamak

A preliminary mechanical analysis has been conducted for the hybrid Central Solenoid coil, designed for a medium-sized tokamak aiming for a fusion power gain Q > 1. To optimize magnetic flux, the CS coil integrates REBCO conductors in its high-field sub-coil and high-Jc Nb₃Sn conductors in the low-field sub-coil. The peak magnetic field reaches 18.3 T at a current of 39.5 kA, producing a magnetic flux of 54.6 V s at a major radius of 3.5 m. A static structural assessment has been undertaken to initially evaluate the integrity of the preload structure. Additionally, a 2D axisymmetric finite element model, incorporating cables, conductor jackets, turn insulations, insulation spacers, pancake insulations, ground insulations, and inter-module spacers, has been developed and simulated using ANSYS's coupled structural-thermal-electromagnetic solver. Given that the CS conductor jacket is subjected to cyclic loads due to electromagnetic forces during operation, estimating its fatigue life is crucial. The jacket fatigue life curves are derived from a fatigue crack growth analysis.