Transmission conductance of a cylindrical tube with wall pumping

Abstract

The concept of transmission conductance is required to describe phenomena occurring in a tube with wall pumping. This is because the gas flow is not constant along the length of the tube but decreases, which implies that the geometric conductance determined by dimensional parameters of the tube cannot be further used. In one of the previous studies, the transmission conductance of a cylindrical tube was analytically derived using the particle balance equation based on the continuity principle. However, the calculated results well agreed with those of the test particle Monte Carlo (TPMC) simulation only when the sticking coefficient was less than 0.1. This is due to the intrinsic limitation of the analytical method, in which the constant conductance of a tube of unit length with uniform wall pumping was used. In this study, we introduced another analytical method based on the cosine law and finite element analysis using the conductance of the tube of unit length as a function of the position in the tube, considering the beaming effect. Using both methods, the relative difference in transmission conductance with TPMC considerably decreased compared to the previous study when the sticking coefficient was greater than 0.1. The results can be used in the design of a non-evaporable getter coated tube or a cryogenic water pump using an adsorbing wall to determine characteristic dimensions. Furthermore, this can be employed in a windowless vacuum coupling or a distributed pumping system for various light source systems.