[APP1] Novel applications, Levitation, Associate components

[APP1-02] Improvements on Cryomodules Operation of the SCL3 Linac for RAON’s 3rd Beam Commissioning

*Minki Lee¹, Seojeong Kim¹, Inmyung Park¹, Junghyun Yoo¹, Hyun Chul Jo¹, Gyuho Lee¹, Jinwook Kim¹, Jaehak Han¹, Jae Hee Shin¹ (1. institute for Basic Science (Korea))

Keywords:

Crymodule operation,Heavy ion accelerator,cavity sensitivity

RAON (Rare Isotope Accelerator complex for ON-line experiments) is a heavy ion accelerator built under the Institute for Basic Science (IBS) in South Korea. The RAON facility consists of the SCL3 linac, which consists of the QWR cryomoule(Quater Wave Resonator, β=0.047, 81.25MHz, 4.5K, single cavity for each module, 22 units) and the HWR cryodmoule(Half Wave Resonator, β=0.21, 162.25MHz, 2K, 2 cavities for each module, 13 units, 4 cavities for each module, 19 units). And, the SCL2 linear accelerator consists of the SSR1 cryomodule (Single Spoke Resonator, β=0.3, 325MHz, 2K, 3 cavities for each module, 23 units) and the SSR2 cryodmodule (Single Spoke Resonator, β=0.51, 325MHz, 2K, 6 cavities for each module, 23 units, 3 cavitis for each module, 2 units). The total capacity of the cryo-plant is 17.7kW, divided between two accelerator lines (SCL3 linac: 4.2kW, SCL2 linac: 13.5kW). SCL3 was completed in Q4 2022, and two beam services were conducted from 2023 to 2024. The cryo-plant for SCL2 is in progress, with pre-commissioning expected to be completed in the second half of 2025 (covering cryo-plant pre-commissioning & SCL2 linac valve boxes (49 units) to the IF separator (Quadrupole magnet’s cryostat (13 units)) valve boxes). The SCL3 linac is currently undergoing its third beam test run, which began in the first half of 2025, and is conducting beam commissioning to improve beam operation time and stability. In particular, some of the superconducting accelerator tubes mounted on the acceleration module are very sensitive (dF (delta frequency)), making it very difficult to control RF (radio frequency system) operation. In order to improve the stability of RF control, we have made several improvement efforts. First, the pressure of liquid helium (4.5K) supplied from the SCL3 plant was changed from 3.0 bar(a) to 2.8 bar(a). Second, an automatic control logic was developed for the cryogenic valve that controls the flow rate of liquid helium supplied from the valve box to the cryomodule and the return valve to maintain a constant pressure after vaporization in the reservoir. Third, the flow rate of liquid helium was controlled by automatically controlling the heater installed in the reservoir (4.5K & 2K) inside the cryomodule. This series of steps allowed us to improve stable RF control and increase beam retention time for high-sensitivity (delta frequency) cavities. In the future, we plan to optimize the operation of the cryomodule based on this.