The Speed of Oil and Mercury Diffusion Pumps for Hydrogen, Helium, and Deuterium

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Abstract
Data on several standard diffusion pumps indicate that the speed for hydrogen may be considerably less than 3.8 times the rated speed for air depending on the jet design, pump fluid, heater input, and speed of the fore pump. Evidence is presented that this reduction in speed is partly the result of diffusion of hydrogen back through the vapor jet from fore vacuum to high vacuum and partly the result of diffusion of hydrogen back out of the jet after entering from the high vacuum side. Measurements of the back diffusion of hydrogen, helium, and air in an experimental pump are correlated with the diffusion coefficient through an extension of the theories of Gaede and Matricon. The mechanism of jet breakdown has been observed with the aid of a glow discharge and a pilot dye.

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