Measurement of Vacuum in Nonuniform Temperature Environments

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Abstract
If temperature gradients exist in a high-vacuum chamber, the residual gas may be of nonuniform density and pressure. If the gas is stationary and reflects according to Knudsen's cosine law, then the flux will remain uniform, despite the temperature gradients. Solutions for the density and pressure are given for parallel planes and for concentric spheres. When estimating pressure from a density observation, the maximum uncertainty is the temperature ratio a2. From a flux observation, the maximum uncertainty is only a. These uncertainties may be reduced by knowledge of the geometry and the accommodation coefficients. The variation of density with position is suggested as a method of measuring the kinetic accommodation coefficient.

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