Design of operation logic for SCL3 cryogenic distribution system for RAON

The operation mode, sequences, and logic of the cryogenic distribution system for Superconducting Linac 3 of RAON are described. The systematic construction of the cryogenic distribution system is introduced, and the roles of transfer lines and instruments are explained. The flow of operation modes and the operation strategies in each operation mode are designed with consideration of the system structure, the requirement of the cryogenic system, and the cryogenic fluid properties. The operation modes are grouped into cool-down process, warm-up process, and steady states in normal operations. The step-by-step operation sequences of the instruments in each operation mode is clarified. In the cryogenic distribution system of RAON, the thermal shield circuits for all cryo-modules are cooled down concurrently, and the fluid mass flow rates are controlled by using virtual flow meters. The most important tasks during the cool-down process of the superconducting cavities are to shorten the cool-down time and keep the steady and low pressure inside the cavities. The cold helium circuits (the SHe, GHe, and VLP lines) are cooled down one by one for the cryo-modules from 300 to 4.5 K. After that, all the HWR cavities are pumped down to 36 mbar at the same time to further cool down to 2.05 K. The warm-up process from 2.05 to 4.5 K is operated without emptying the reservoirs. The cryogenic plant and the CDS are warmed up together by circulating the helium gas.