Commissioning Results of Cryogenic Helium Plant for Korean Heavy Ion Accelerator After a Three-Year Overhaul

The Institute for Rare Isotope Science (IRIS) has two large-scale cryogenic helium plants (hereinafter referred to as”cryoplant”) for the Korean heavy ion accelerator. Each cryoplant is designed to perform 2.05 K operation of the superconducting linear accelerator (SCL). This paper focuses on the smaller unit, the SCL3 cryoplant, which provides simultaneous cooling capacity of 10,250 W at 45 K, 1040 W at 4.5 K and 910 W at 2.05 K. The SCL3 cryoplant was handed over from the manufacturer in August 2022, and has been operated by IRIS since then. A major overhaul was suggested over a three-year interval in preparation for long-term continuous operation so we executed the overhaul from October 2024 to March 2025. The overhaul included the replacement of consumable parts in the warm compressors and 2.05 K warm pumps as well as renewal of coalescing filters and activated carbon to eliminate residual oil from the compressed helium stream. On the coldbox side, critical filters such at the coldbox inlet and the turbine gas bearing inlet were also inspected. After the overhaul, a single refrigeration commissioning test was conducted to validate the mechanical integrity and operational performance. While several minor issues were identified during the test, the system demonstrated acceptable stability. This paper presents the commissioning procedure, observed minor problems, and evaluation of system performance, along with a brief overview of the overhaul activities.