| 摘要 |
In an apparatus for removing a selected first gas from a chamber at a controllably variable pumping speed while maintaining a substantially constant pumping speed for removing a second gas from the same chamber, a flow restricting device is disposed between the chamber and a device that pumps the first gas. The flow restricting device comprises a stationary member having an apertured portion through which the first gas can flow from the chamber to the pumping device. Restriction of the flow of the first gas to the pumping device is accomplished by covering the apertured portion of the stationary member with a movable member to the extent necessary to provide the desired pumping speed for the first gas. The stationary member is maintained at a cryogenic temperature higher than the condensation temperature of the first gas, but at a value at which the second gas condenses. In one embodiment, the stationary member is maintained at the desired cryogenic temperature by being mounted in intimate thermal contact with a cryogenic fluid reservoir. In an alternative embodiment, the stationary member is mounted in intimate thermal contact with the warmer stage of a two-stage cryogenic pump.
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