Simulation and experiment of CRAFT NNBI cryopump

The cryogenic vacuum system is an important subsystem of Comprehensive Research Facility for Fusion Technology Negative Neutral Beam Injector, which provides vacuum environment support for various experiments related to the beam generation and transport process. In the paper, a simulation and experimental study of the Comprehensive Research Facility for Fusion Reactor Negative Neutral Beam Injector (CRAFT NNBI) cryopump performance has been carried out. The Beam Line Vessel (BLV) and its components are modeled by Solidworks, the pressure distribution, gas molecular velocity distribution and adsorption uniformity of the crysorption pump in the BLV are analyzed by simulation using the Molflow software, at the same time, the performance of the south cryopump is tested experimentally using in-situ measurement method. The simulation results show that the average pressure near the Neutralizer is 8.5*10^-3 Pa, the average pressure near the Electrical Residual Ion Dump (ERID) is 8*10^-3 Pa, and the average pressure near the Calorimeter is 9*10^-3 Pa. The adsorption percentage fluctuates around 12%, which indicates that single structure plays the function of adsorption efficiently, the theoretical pumping speed of the south cryopump on H2 was calculated to be 7.34*10⁵ L/s, total theoretical pumping speed of two cryopumps can reach 3.67*10⁶ L/s. The experimental results showed that when the south cryopump was operation, the pressures near the Neutralizer were 2.8*10^-2 Pa, the pressures near the ERID were 2.7*10^-2 Pa, and the pressures near the Calorimeter were 7*10^-3 Pa, the actual pumping speed of the south cryopump on H2 was 6.37*10⁵ L/s, total actual pumping speed of two cryopumps can reach 3.1*10⁶ L/s.