Cryopump Pumping Performance Estimation Using Flow Meter Method

Abstract

The pumping performance of cryopump, ULVAC CRYO-U10PU, is estimated by the flow meter method, which is widely used in the estimation of the pumping performance of the turbo molecular pump for inlet pressure greater than 1.0E-04 Pa. The test dome is connected directly with the cyropump, and the inner diameter is the same as the inlet port of the pump. The pirani gauge and the ion gauge are equipped on the peripheral of the test dome. Three flow meters hybrid the needle valves are used to control the introduced gas throughput and two types of gas, nitrogen and argon, are introduced. The variations of the temperature of the first stage of the cryopump and the test dome pressure relative to the operating time of cryopump are discussed. The pumping speed and throughput of the cryopump versus to the test dome pressure that is considered as the inlet pressure of cyropump are plotted and compared to the values described in the catalog of ULVAC. Finally, the residual gas analysis is made to investigate the residual gas in the test dome. And the first stage temperature is recorded after the cryopump is turned off According to the measurements, the temperature of the first stage of cryopump is in the steady state condition after 200 minutes of the starting of the cryopump. The pumping speed for nitrogen is between 919 and 2,170 Liter/sec for the inlet pressure range of 1.0E-03 to 0.5 Pa. For argon, the pumping speed is in the range of 1,770 to 4,060 Liter/sec for the inlet pressure from 1.0E-03 to 1.5E-01 Pa. The ULVAC catalog shows the pumping speed for nitrogen and argon are 2,300 and 2,000 Liter/sec, respectively. The partial pressure of hydrogen and water at the status of the ultimate pressure operating condition is high. The retrieved time from normal operating temperature of the cryopump to the room temperature is over 300 minutes after the pump turned off