The Mechanical Analyses and Structural Optimization of CSMC Preload System under Multi-load Cases

In order to accumulate experience in the design and manufacturing of the toroidal field coils for the China Fusion Engineering Test Reactor, a model coil of mixed Nb3Sn-NbTi superconducting magnet with a maximum magnetic field variation rate of 1.5 T/s has been developed at the Institute of Plasma Physics, Chinese Academy of Sciences. The preload system, as one of the key components of the model coil, plays a crucial role in maintaining the overall integrity and stability of the model coil. First the magnetic field and electromagnetic forces of the model coil under extreme conditions are calculated based on Maxwell's equations. Then, the mechanical performance of the model coil at room and cryogenic temperatures is analyzed. To addressing the issue of excessive stress in the preload components of the model coil under preload, several optimization design schemes are proposed and iteratively analyzed. Finally, stress linearization is performed, and stress evaluation is conducted based on the analytical design. The assessment results indicate that certain optimization schemes enable the preload components to fully meet the operational requirements at both room and cryogenic temperatures. The outcomes presented in the paper will provide reference for the subsequent design and manufacturing of the central solenoid coil.