Abstract
A transmission probability W of gas molecules passing through a vacuum component is usually calculated using the Monte Carlo method. In the calculation, it is generally assumed that gas molecules are introduced to a smooth surface and scatter with cosine low. Since the W is influenced by the shape and/or roughness of the surface in practice, the precise calculation of W requires the inclusion of surface geometry. The conventional Monte Carlo method, however, needs very long time to calculate the W for a cylinder with many corrugations, in other words, rough surface. In this paper, a new method to decrease the time for a calculation with rough surface is described. In the new method, the scattering angle distribution distorted by corrugations is analytically calculated. The distorted distribution is used to determine the scattering angle of the gas molecules at the surface. In the case of a cylinder with the ratio of length to the radius L/r of 5, the ratio of the W with V-shaped corrugations to that without corrugations is 0.77 at minimum. Results of the calculation were obtained by both the new method and the conventional method, and are identical within 0.5%. The time required by the new method was more than 100 times shorter than that by the conventional one.
