Analysis of the influence of the structure of radiation shield on its transmission probability for a cryo-condensation pump

The cryo-condensation pump used in EAST-NBI is composed of cryo-condensation panels cooled by liquid helium and radiation shields cooled by liquid nitrogen. The transmission probability of radiation shields has great influence on the performance of the cryo-condensation pump. The Monte-Carlo method is applied to simulate the trajectories of the deuterium molecules and to study the effects of the structure of the radiation shields on the transmission probability. By adding imaginary walls, the distribution of positions and flying directions of the molecules is presented. The results indicate that the uniformity of the molecules is the direct factor to influence the transmission probability.