Development of cryogenic systems for the RAON accelerator

The rare isotope accelerator complex for ON-line experiment (RAON) heavy ion accelerator accelerates heavy ions by using two superconducting acceleration lines (SCL3 and SCL2) and separates, dumps, and focuses rare isotopes generated by using superconducting magnets to collide them with a target. It serves as a large-scale research facility for rare isotope science. Large-scale cryogenic systems are essential for creating and maintaining cryogenic conditions necessary for the superconducting systems to operate effectively. The RAON cryogenic systems consist of two cryogenic plants, which include a helium recovery, purification, and storage system, a helium distribution system, cryomodules, a cryogenic control system, and two test facilities for measuring the performance of mass-produced superconducting devices under cryogenic conditions. The cryogenic systems are developed based on the requirements and roles to ensure the stable operation of superconducting systems at cryogenic temperatures, specifically at 4.5 K and 2.05 K. These systems have been developed over a period of 5 years and 6 months, from design to commissioning and operation. The cryogenic commissioning of SCL3 was successfully completed in 2023. For 10 months, all cryogenic systems have been functional and have supported the cryogenic conditions required for the commissioning of SCL3 RF and beam dynamics. This paper primarily reviews the cryogenic systems related to SCL3, focusing on the design aspects and lessons learned from the first commissioning and operation of SCL3.