-
Author(s):
K. Akaishi, M. Nakasuga and Y. Funato
-
Title:
True and Measured Outgassing Rates of a Vacuum Chamber with a Reversibly Absorbed Phase
Date of publication:
Mar. 2000
-
Key words:
outgassing rate, outgassing equation, surface coverage, sticking probability, mean residence time, Temkin isotherm, 304 stainless steel chamber
-
Abstract:
A pump down model for a vacuum chamber with a reversibly absorbed phase is presented. The outgassing equation which predicts the variation of coverage at the wall surface of a vacuum chamber with time is derived. Then the measured and the true outgassing rates are defined. The theoretical measured outgassing rate shows only a very weak dependence for pumping speed. This prediction is opposite to the experimental result that the measured outgassing rate depends significantly on pumping speed. It is discussed that thte experimental measured outgassing rate must be described as the product of the effective pumping speed and the measured pressure in the pumped chamber, in which the measured pressure is equivalent to the equilibrium pressure of the wall surface described by the equilibrium adsorption isotherm as a funcion of the shifted surface coverage theta - theta Delta by a asmall coverage theta Delta from the coverage of a pumping point theta.
-
|
