Thermal-hydraulic analysis of the cool-down for the CFETR TF coil using the 4C code

• During CFETR TF coil cool-down, temperature gradients must be small. • The maximum temperature within the TF coil cannot be directly measured. • The validated 4C code is used to numerically simulate the cool-down. • Optimized cool-down strategy are proposed for future experiments. The China Fusion Engineering Test Reactor (CFETR) will be a superconducting tokamak featuring sixteen toroidal field (TF) coils; a full-size TF coil, based on a national scientific research project, has been designed and is currently being built. The first cool-down test of the TF coil is foreseen to take place in 2025. During the entire cool-down process, it is necessary to ensure that the temperature difference between any two positions of the TF coil is <50 K to avoid irreversible damage to the coil caused by excessive thermal stress. However, the maximum temperature ( T max ) within the TF coil cannot be directly and accurately obtained through experimental measurements; therefore, the thermal hydraulic analysis is crucial to prepare the cool-down strategy of the coil. In this paper, the first cool-down analysis of one CFETR TF coil is completed using the 4C code. The code is based on a 1D model of the helium flow inside the cable-in-conduit conductors coupled to a set of 2D cross sections of the steel structures, where the heat conduction is modeled. The thermal coupling between the turns and the pancakes, as well as the coupling between winding and casing, is also considered. The maximum temperature evolution within the magnet is computed and the optimized cool-down strategy (inlet temperature, inlet and outlet pressure evolution) is proposed.