JT-60SA Operational Status and Future Upgrade

JT-60SA (R =3 m, <tex-math notation="LaTeX">a </tex-math> =1.2 m) will be the world’s largest superconducting tokamak until ITER starts operation. Its assembly was completed and its integrated commissioning started in 2020. Vacuum integrity and the superconductivity of all magnets were confirmed and the design toroidal field (TF) of 2.25 T was reached in March 2021. However, operations were interrupted due to an arc at the terminals of the largest poloidal coil. Since then, to reduce the risk of such events, extensive improvements have been made to the insulation of the magnet system, to the power supplies, and to vacuum instrumentation. Operations will restart in 2023 when it is expected to produce the first tokamak plasma before a major upgrade begins later in the year. This will add 18 ports, 23 MW of neutral beam injection, 1.5 MW of additional electron cyclotron resonance heating (ECRH), and extensive plasma diagnostics. Within the vacuum vessel, a pumped carbon lower divertor, stabilizing plates, carbon outer first wall, resistive wall mode correction coils, fast plasma position control coils (FPPCCs), and error field correction coils (EFCCs) will be installed. Commissioning in 2023 will restart cautiously as the sufficiency of the improvements is assessed. The extent to which the design performance of the basic tokamak device may be demonstrated will be determined on the basis of further tests (e.g., global Paschen test, voltage holding at 4 K) and operating experience. To support its research aims with high-performance, long-pulse (100 s) experiments JT-60SA has an extensive plan for enhancements in the coming years. The next improvements planned for plasma heating and fueling, power handling, disruption mitigation, and diagnostic capability are outlined.