Concept of the transmission conductance

The geometric conductance defined in a normal tube is not useful for describing transmission characteristics of a sticky tube with wall pumping in which the gas throughput is not uniform. To find a proper solution to this problem the concept of transmission conductance is introduced instead of the geometric one. The transmission conductance is expressed as a function of the pressures and the throughputs at the inlet and outlet of the sticky tube. Applying the concept of the transmission conductance to the tubes with wall sorption and/or wall outgassing, then a few selected mathematical expressions of the transmission conductance and adsorption speed are derived. A combination rule of the transmission conductance for constructing a composite tube, equivalent to the Oatley's principle for normal tubes, is also discussed. Comparison of analytic calculations and Monte Carlo simulations shows good correspondence as long as the sticking coefficient on the tube wall is not much larger than 0.1. (C) 1998 American Vacuum Society. [S0734-2101(98)03206-0].