Warm-up Time Estimation in case of Failure for the S³FEL Accelerator Cryogenic System

Abstract Shenzhen Superconducting Soft X-Ray Free Electron Laser (S 3 FEL) is under construction in Shenzhen, China by the Institute of Advanced Science Facilities (IASF). The cryogenic system is one of the most important systems in S3FEL, which provides a cryogenic environment for the superconducting accelerator. Once the cryogenic system shuts down in case of failure, the superconducting accelerator will stop running. Then, the pressure in the accelerator pipes will increase, which maybe caused safety valve jumping or cryogenic lines breaking. The warm up time from operation pressure to the specified relief pressure is helpful to select reasonable relief pressure and protective measures. In the present work, the calculations of the warm up time with different liquid helium levels under four specific operational faults and two initial conditions are conducted. In a case of liquid helium level with 70%, the warm up time of upstream and downstream were about 6.8 hours and 10.9 hours at an initial condition of 2 K superfluid helium, while they were about 4 hours and 6.1 hours at an initial condition of 4.5 K saturated liquid helium. The difference between upstream and downstream warm up time was mainly caused by the different lengths of cryogenic transfer line. Moreover, the variations of liquid helium level with time at a specified condition were also calculated. The results presented in this paper will provide useful information for the cryogenic system safety design and accelerator operation modes.