Sorption Pumping of Residual Gases at Cryogenic Temperatures
Since the inception of space vacuum simulation, there has been a need to create, at least in a small test volume, the pressure existent in space, 10-12 to 10-16 torr. Although this level of vacuum has been achieved in research-type facilities, requiring extreme care and expense, the conduct of a test in such a system has not become a routine matter. Reserve pumping capacity must be provided at ultrahigh vacuum to handle the out-gassing load of the test article and, hence, to maintain the vacuum level. Cryogenic pumping, which provides large pumping surfaces and high pumping speeds for the condensable gases, has proven to be a successful technique for the evacuation of test chambers. It is generally recognized that a vacuum greater than 10-14 torr can be created in a leak-free vessel having its interior surfaces maintained at 2.5°K. However, the operation and maintenance of surfaces at liquid helium temperatures and lower present many complex engineering problems. Further, a cryogenic surface is able to pump only those gases with a partial pressure in the test chamber greater than the vapor pressure of the gas at the cryosurface temperature. For example, at 10-11 torr, surface temperatures below 3°K are necessary to pump hydrogen.
KeywordsHeat Load Cryogenic Temperature Test Volume Diffusion Pump Valve Plate
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- 1.R. E. Southerlan, “Cryosorption Properties of Molecular Sieve 5A, Carbon Dioxide and Water Frost Near 20°K,” presented at 11th National Vacuum Symposium, Chicago, Ill. (October 1964).Google Scholar
- 2.R. E. Southerlan, “10–22°K Cryosorption of Helium on Molecular Sieve 5A and Hydrogen on Condensed Vapors,” AEDC-TR-65–49 (May 1965).Google Scholar
- 3.R. A. Hemstreet, “The Cryosorption Pumping of Hydrogen at 20oK,” AEDC-TDR-64–100 (May 1964).Google Scholar
- 4.S. A. Stern, “The Cryosorption Pumping of Hydrogen and Helium at 20°K,” AEDC-TDR-62–200 (October 1962).Google Scholar
- 5.R. E. Honig and H. O. Hook, “Vapor Pressure Data for Some Common Gases,” RCA Reviezw 21(3):360 (1960).Google Scholar