Simulation of the JT-60SA Supercritical Helium Toroidal Field Coil Loop During Fast Safety Discharge Using Simcryogenics. Comparison With Experimental Data and Extrapolation to Higher Currents

The JT-60SA fusion experiment is under commissioning at Naka, Japan (2023). When a fast safety discharge (FSD) of the toroidal field coils (TFC) current occurs, the procedure is to close the supercritical helium (SHe) supply of the magnets from the auxiliary cold box to release the heated and pressurized helium of the coil and its structure into a quench tank to avoid over-pressurizing the loop. To restart normal operation, the evaporated helium must be re-liquefied to return into the loop. This can take up to 48 hours. The maximal pressure reached in the loop during FSD has to be predicted to assess the necessity to open the quench relief valve (QRV). If opening the QRV is not necessary, it will save time during the commissioning and during future operation. Simcryogenics (Bonne et al., 2020) is used to model the whole cryo-magnetic loop 1 dedicated to supply SHe for the TFC Winding Pack (WP), the TFC structures and CS structures. It means that the piping, Cable in Conduit Conductor (CICC), TFC structures and CS structures, which belong to the TFC loop, are modeled thermally and hydraulically. The heat loads that are generated during FSD and that are applied to the simulation are issued from an ad-hoc simulation. This paper presents the comparison between experimental and predicted behavior of TFC FSD at 15 kA and 18 kA and extrapolates it for higher current, such as the nominal current of 25.7 kA. This paper gives the value of the FSD current for which the TFC loop helium must be released into the quench tank, meaning that the loop pressure would be expected to lead to the safety valve opening.