Effects of cryopump on vacuum helium leak detection system

A molecular pump is always used as the main pump of the vacuum leak detection system because of its strong ability for pumping helium. But the pumping speed of a molecular pump is not enough for large vacuum chamber. A cryopump is a clean, oil-free and high pumping-speed vacuum pump. If a cryopump is used as the main pump of the vacuum leak detection system, the number of the pumps will decrease. This paper describes the experiments on vacuum leak detection system with cryopump as a main pump, and analyses the phenomena in the experiments. The results show that the cryopump decreased the vacuum pressure of the system significantly, but it had nearly no influence to the system sensitivity. The response time and the clean-up time of the leak detection system with only molecular pump were both 3 min. But the response time of the leak detection system with both molecular pump and cryopump was 10 min-20 min, and the clean-up time of the system was longer than an hour.