Thermal performance analysis of cryogenic system for cooling of superconducting magnets at 4K temperature level

Cryogenic system in fusion research tokamak integrates many components, i.e., heat exchangers, valves, cold circulating pumps, cold compressor etc., in various configurations for the cooling of superconducting (SC) magnets like Toroidal Field (TF), Poloidal Field (PF) and Central Solenoid (CS). Helium refrigerator/liquefier (R/L) serves as a source of cold power for the cryogenic cooling of magnets at 4 K temperature level. However, normally the cryogenic cooling of the SC magnets is accomplished indirectly using the secondary circuit by the use of cold circulating pump, which circulates when the supercritical helium in closed circuit and rejects the heat from SC magnets to the Liquid Helium (LHe) bath which is maintained at ~4 K temperature level by the helium (R/L). This arrangement provides flexibility for the operation of SC magnets, which operates in pulsed manner, and still establishes stable operation for the helium (R/L). There are various configurations that are possible for LHe bath and cold compressor arrangements, i.e., there is a common LHe bath for all SC magnets or individual bath for each SC magnet with either individual cold compressor or common cold compressor for each bath. Thermal system modeling and analysis of the different cryogenic cooling configuration reveals the optimum configuration satisfying the main function of cryogenic cooling of SC magnets with required thermal performance.