The superconducting tokamak JT-60SA is part of the Broader Approach Programme agreed between Japan and Europe. CEA is in charge of the cryogenic system procurement including the Warm Compression Station, the gas storages, the Refrigerator Cold Box and the Auxiliary Cold Box (ACB) which has to be installed on the JAEA Naka site in 2016. This paper summarizes the updated cryogenic requirements for the tokamak JT-60SA cryogenic system. The cryogenic system has a refrigeration capacity of about 9 kW equivalent at 4.5K, to supply cryopump panels at 3.7 K, superconducting magnets and cold structures at 4.4 K, HTS current leads at 50 K, and thermal shields at 80 K. This paper presents the static and variable heat loads of the different cooling loops and the results of thermohydraulic calculations to derive the transient heat loads at the interface between the magnet system cooling loops and the Auxiliary Cold Box.

The JT-60SA cryogenic system with a refrigeration capacity of 9.5 kW at 4.5 K consists of Refrigerator Cold Box (RCB) and Auxiliary Cold Box(ACB). The RCB provides cold helium to the ACB, high-temperature superconductor current leads, and an 80 K thermal shield. The ACB supplies supercritical helium at 4.4 K / 0.5 MPa by cold helium circulation pumps to a superconducting magnet system through the heat exchangers in a liquid helium tank. In a tokamak type fusion device, superconducting coils, CS and EF, are operated as dynamically controlling their transport currents to sustain plasma operation.Hence the heat load variations caused by AC losses could disturb the operation of the cryogenic system. The JT-60SA cryogenic system has an active control mechanism to mitigate a substantial dynamic of heat load for the stable operation of the warm helium compressors and turbines. During the commissioning of the cryogenic system, the active control mechanism demonstrated a stable operation of the cryogenic system. A cool-down operation of the cryogenic system started in October 2020. This paper reports the specifications of the cryogenic system, a result from a control test for variable heat load, and thermal analysis result at toroidal field coil operation.