Simulation study of effective pumping speed of divertor pumping system for CFETR with COMSOL Multiphysics

In this study, COMSOL Multiphysics is used in the numerical analysis of a neutral gas in the divertor pumping system of the China Fusion Engineering Test Reactor (CFETR). The slip boundary condition modified Navier-Stokes equation and angular coefficient methods are used for simulation. The corresponding divertor inlet pressures are 1 Pa under plasma discharge and 1 x 10-5 Pa at the pumping limit. Additionally, the throughput and flow conductance of the divertor pumping system are calculated. The effective pumping speed (EPS) of a single cryopump in a vacuum chamber is also computed. Results indicate that the EPS values of the single cryopump from the divertor inlet are 33.35 and 16.91 m3/s, corresponding to the divertor inlet pressures of 1 and 1 x 10-5 Pa, respectively. By comparing the simulation results with those of the direct simulation Monte Carlo and test particle Monte Carlo methods, the feasibility of COMSOL Multiphysics was verified with a maximum error of less than 5%. This study provides technical support to the subsequent optimization of CFETR divertor pumping channels and EPS evaluation.