Ultimate pressure cryopumps

If gases like H2, He and Ne are to be trapped, the pump must be cooled to 4.2 K. Detailed information on cryopumping can be found in ref. [10]. Ultimate pressure of the order of l(U5torr can be achieved. 

NEG pumps are mostly used in combination with other UHV pumps (turbomolecular and cryopumps). Such combinations are especially useful when wanting to further reduce the ultimate pressure of UHV systems. 

CRYOPUMP. 11) An exposed surface refrigerated to cryogenic temperature for the purpose of pumping gases in a vacuum chamber by condensing the gas and maintaining the condensate at a temperature such that the equilibrium vapor pressure is equal to or less than the desired ultimate pressure in the chamber. 

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