Cryogenic System for the Superconducting Tokamak HT-7U

HT-7U is a fully superconducting tokamak. All of the toroidal field and poloidal field superconducting magnets are made of NbTi superconductor and are designed to operate at 3.8 K in the steady-state operation mode. The magnet system will be cooled with forced-flow supercritical helium to this temperature level with an equivalent refrigeration capacity of ~2 kW/4.4 K. To satisfy this requirement, a helium refrigerator is designed to be able to provide the cooling power at 3.5, 4.5, and 80 K for the coils, supports, and thermal shields. The refrigerator can also produce liquid helium for the cooling of the current leads. This paper describes the cryogenic system of HT-7U, the refrigeration process and helium plant, and the forced-flow cooling requirement of the superconducting magnets.