Capability of obtaining extreme high vacuum by commercial G-M refrigerator-cooled cryopump

Abstract

The authors investigated the possibility of achieving an Extreme High Vacuum (XHV) environment by employing a commercial G-M refrigerator-cooled 10 K cryopump instead of a costly 4 K refrigerator-cooled cryopump. In order to minimize the outgassing rate which might disturb the evaluation of the cryosorption effectiveness in the XHV region, all vacuum walls of the cryopump vessel and the test dome were made of 5052 aluminum alloy the surfaces of which had been specially treated. After 70 days system conditioning, the ultimate pressure (between 3 and 5 × 10 −11 Pa) was obtained repeatedly by 3 or 4 days evacuation. The partial pressure behavior of several gases was observed by changing the cryopanel temperature to evaluate the ultimate pressure limit of cryosorption pumping at the relatively higher temperature of 10 K. The experimental result shows that the cryosorption pumping at 10 K is still effective below 10 −11 Pa.