JT-60SA TF coil quench model and Analysis: Joule energy estimation with SuperMagnet and STREAM

Abstract

In the framework of JT-60SA Tokamak commissioning (Japan, 2021), all coils have to be cooled with supercritical helium forced-flow at the temperature of 4.5 K in order to reach superconducting state before energization. An important issue is to predict the Joule energy dissipated in Cable-In-Conduit Conductors (CICC) and the maximal temperature reached in case of an incidental quench occurrence. Therefore, quench simulations were performed on the Toroidal Field Coil (TFC) with the STREAM (Superconductor Thermal hydraulic and Resistive Electrical Analytical Model) code and with the SuperMagnet code (CryoSoft), coupling THEA (thermal hydraulic and electrical 1-D CICC model) and Flower (thermal hydraulic network model). The quench event was simulated for one TFC at nominal conditions of tokamak operation. External energy deposition over each pancake’s first turn of the coil at the peak magnetic field location was applied for initiating the resistive transition. This way, the computed Joule energy dissipated by one TFC is conservatively evaluated to be 5.65 MJ. The Joule energy dissipation depends strongly on quench initiation conditions and on the number of fully and rapidly quenched pancakes (maximal quench propagation velocity of 19.5 m/s). Some further analyses were performed on the acceptance quench test realized at the Cold Test Facility (CEA Saclay, 2018) on TFC02. The different calculation results (helium temperature, mass flow rate in upstream and downstream manifolds, normal length propagation) are presented in the following study and are consistent with the measurements. This analysis brings information on the limits and the ability of STREAM code to model quench behaviour in CICC coils cooled by forced flow of supercritical helium. This tool could be useful for tokamak magnets protection during quench event and safe operation, notably thanks to its fast computing time.