Stress Analyses of the Support Structure and Winding Pack of the Superconducting TF Coil in National Centralized Tokamak

The design activity of the support structure of Toroidal Field (TF) coil is progressed for the National Centralized Tokamak (NCT). For this device, the new support structures of the TF coil is proposed. In the new design, connection keys between coil case and shear panel are adopted in order to decrease the movement of shear panel from coil case which induces the displacement of TF coil during coil operation. For the stress analysis of new structure, FEM model with full-solid elements are developed to evaluate the behavior around the connection keys. The electromagnetic force induces strain and stress on the winding pack which affect the performance of superconductor such as Nb₃Al that is adopted for TF coil in NCT. Therefore, longitudinal strain and transverse stress on the winding pack during coil operation are inspected. For the new design of TF coil, the maximum displacement is 6.4 mm around the upper shear panel and maximum Tresca stress with 415 MPa appears on the shear panel at the midplane. This value is within the allowable stress of SS316LN at 4 K, 547 MPa. For the winding pack, longitudinal strain is evaluated with -0.03 to +0.07%, and transverse stress is evaluated with <40 MPa at the place with the maximum field. These values are too small to affect the critical current of Nb₃ Al conductor. Therefore, it is confirmed that the stable operation of superconductor is insured on the new structure of TF coil