Design of the superconducting coil system in JT-60SA

Recently, design of superconducting coils system in JT-60SA is revised from the previous design of JT-60 modified tokamak, NCT. The superconductor of toroidal field (TF) coil is exchanged into NbTi, so that the designed BTR is economically established while dimension of the TF coil becomes larger. Design of poloidal field (PF) coils is optimized to realize the broader operational space of plasma configurations, e.g. double-null plasma operation with the low aspect ratio and the operation with ITER similarity configuration. In particular, central solenoid (CS) design is revised to supply the required flux swing in the narrow space that is limited by enlargement of TF coil, and the maximum field in new design of CS becomes 10 T. For this design of CS, the stress at the conduit of conductor is analyzed and fatigue life is evaluated. Therefore, it is clarified that thickness of conduit should be increased with 0.4 mm at least to make the maximum stress less than the fatigue limit without major changes for the radial build.