JT-60SA is the largest Tokamak fusion experimental device worldwide, with a superconducting magnet system. JT-60SA comprises 18 toroidal field （TF） coils, six equilibrium field （EF） coils, and four central solenoid （CS） modules. Tokamak assembly was completed in March 2020. The cooldown of the magnet system for the integrated commissioning test and the individual magnet energization test began in October 2020. TF coil achieved 100 % current （25.7 kA） operation, and EF2~6 and CS1~4 achieved ± 5 kV operation. However, EF1 caused a double grounding fault in the high voltage energization test and was electrically shorted. The incident was investigated, followed by repair and reinforcement of insulation. It took approximately 2 years to develop the insulation reinforcement procedures and high voltage tests in vacuum conditions and complete the reinforcement of the insulation and high voltage tests, allowing us to achieve the first plasma operation. This paper describes the magnet and cryogenic systems, recovery activities after the EF1 incident, and the integrated commissioning test preparation.

JT-60SA cryogenic system comprises a main refrigerator cold box, auxiliary cold box, warm helium compressor, control system, and utility system （cooling water and instrumentation air）. The total equivalent refrigerator power is 9.5 kW at 4.5 K. The cryogenic system supplied 4.4 K supercritical helium to the magnet system, 50 K pressurized helium gas to high-temperature superconducting current lead, and 80 K pressurized helium gas to the thermal shield. Before cooldown, cryostat helium leak testing and helium gas purification were performed. It took approximately 41 days to cool the magnet system from room temperature to superconducting transition temperature. During operation, the refrigerator was stopped three times because of electrical grounding problems and incorrect control parameter values in the cold rotation machine control system. Except for problems, the cryogenic system was steadily operated. This paper describes the cryogenic system operation results during cooldown and magnet operation.

The complete superconducting toroidal field (TF) magnet of the JT-60SA tokamak (R=3 m, a=1.2 m) was first energized in February 2021 and reached its full design field (2.25 T on-axis) on 02 March. Tokamak operation was interrupted due to an arc on the largest poloidal field coil EF1 but restarted in 2023 following extensive improvements. In 2023 the TF magnet was used frequently during August – December, during commissioning of the magnet system, plasma operations and in support of electron cyclotron wall cleaning (ECWC).

Ten JT-60SA poloidal field （PF） coils contain four central solenoid coils and six equilibrium field coils. Of these, some PF coils were successfully energized up to 5 kA and some coils were energized up to 10 kA for an individual operation test. After the test, all 10 PF coils were simultaneously operated along the current pattern of plasma operation with a maximum current of 5 kA for an integrated operation test. After the completion of commissioning tests, plasma operation was initiated and no quench occurred during the entire operation period. JT-60SA generated the first tokamak plasma in October 2023, and the plasma current reached 1.2 MA. The energization results of the commissioning test and plasma operation are reported in this paper.

The safety system for JT-60SA superconducting magnet was developed for 1） signal processing of quench detectors; 2） protecting superconducting components, including magnet, thermal shield, feeder, and high temperature superconducting current lead; and 3） transmitting protection interlock signals as well as protecting operation data. This paper introduces the safety system functions. Based on the magnet systemʼs withstand voltage performance in a vacuum condition, a vacuum pressure monitoring system is essential to protect the superconducting magnet system from insulation incidents. A vacuum monitoring system has been developed, and response time has been measured when the vacuum is degraded. The response time characteristics of the vacuum monitoring system are reported.