Cryogenic system for Superconducting Tokamak

The purpose of this paper is to give an overall view of the superconducting coil system and to describe the details of the helium cryogenic system for Superconducting Tokamak Test Assembly (STTA) which is a medium-size superconducting tokamak and designed on the basis of tentative parameters chosen through the design work at the Japan Atomic Energy Research Institute (JAERI). The STTA is composed of the superconducting toroidal field (TF) coils which have similar configurations to those of a test coil for the Large Coil Task (LCT), the superconducting poloidal field (PF) coils whose diameter is 2-10 m, and other facilities required for the power generation. The capacity of the helium cryogenic system for the STTA is specified to be 3,000 liters of liquefaction per hour or 12 KW of refrigeration at 4.4 K, reliable for more than 6,000 hours, and high energy efficiency more than 1/500. The cryogenic system can cool the STTA with cooling weight of 1,000 tons down to 4 K in 10 days, and absorb the heat load of 5,000 W and 1,500 1/h at 4.4 K. In addition, the cryogenic system is designed to be able to produce and supply 650-g/s, 4.5-K, and 1.0-MPa supercritical helium to the TF and PF coils. This system is expected as a unit of the cryogenic system for Fusion Experimental Reactor (FER) after JT-60.