Effect of Cool-Down Speed on Temperature Distribution in the JT-60SA Superconducting Coil

The JT-60SA central solenoid (CS) module is cooled to the operating temperature by the gas and supercritical helium. The cool-down tests of center solenoid model coil (CSMC), manufactured to validate the CS module manufacturing process for JT-60SA, showed that the maximum temperature in the CSMC occurs at the innermost turn of the coil. In the JT-60SA cool-down operation, the temperature can only be measured at the flow pipes connected to the outlet and inlet. Therefore, the maximum temperature in the CS module, which has a flow path similar to that of the CSMC, cannot be measured directly. In this study, we developed an analytical model to estimate the temperature distribution for the helium, strands, and jacket in the conductor from the measurement of the JT-60SA CSMC cool-down test. When the inlet temperature of the CS module in the JT-60SA cool-down test in 2023 was used for the inlet temperature in the analytical model, the coil was safely cooled to the operating temperature. Furthermore, the maximum temperature difference in the CS module and the cool-down speed were evaluated when the inlet was adjusted to keep the temperature difference between the inlet and outlet constant.