Studies on pumping behavior of a test cryopumping facility

Since more than a decade cryopumps are used as one of the reliable vacuum pump to get clean ultra-high vacuum. The pumping performance of a cryopump is always depends on the type of sorbent used, operating temperature of pumping surface and the type of gases. There is always a variation of the reported pumping speed towards the actual experimental pumping speed. Hence the actual pumping speeds were measured as per the American Vacuum Society (AVS) standard for the different gases and compared with the reported values for the test cryopump Marathon® CP-12. Experiments were performed for the operating pressure range of 5E-7 mbar to 1E-4 mbar with a calibrated throughput varying from 1mbar-ltr/s to 1E-3 mbar-ltr/s. It was observed that the pumping speed for a particular gas always depends on the working pressure and the operating temperature. Measured pumping speed values are in good agreement with the catalogue value for the operating pressure range of 3E-5 mbar to 4E-5 mbar.