Key features of the KSTAR helium refrigeration system

► The KSTAR HRS demonstrated 9.5kW at 4.5K during the commissioning period. ► The KSTAR HRS has supported the cool-down of KSTAR and the plasma operation successfully. ► The cooling power of the HRS during KSTAR campaign was maximum 8.2kW @ 4.5K. KSTAR is a fully superconducting (SC) tokamak consisting of 30 magnet coils made of Nb3Sn and NbTi. To keep the SC magnets at proper operating conditions, all cold components of KSTAR such as the SC bus-lines, current leads, and thermal shields must be maintained at the respective cryogenic temperatures by using a helium refrigeration system (HRS). The main components of the HRS can be classified into the warm compression system (WCS) and the cryogenic systems according to their operating temperature levels. The HRS had been manufactured, installed and commissioned until March 2008 and has been operated for KSTAR campaign since then. In this paper, the result of the commissioning, operation and reliability record of the KSTAR HRS will be presented.