Cryopump regeneration studies

A cryopump (APCI Model HV202‐8C) connected to a pump speed test dome was used to evaluate the time and effectiveness of its regeneration using alternate methods of purging and heating the pump. Regeneration effectiveness was determined by measuring the pumping speed and helium adsorption capacity of the charcoal after cool down. The pump was loaded with 8 g of water and 10 std.L of argon prior to regeneration. For all tested regeneration methods the helium speeds were within 80% of the maximum speed. Warm up and evacuation without extra heat or a purge followed by cooling can be done in 4 h and 15 min. Regeneration was accomplished in 2 h and 45 min using a heater on the outside of the housing and a nitrogen purge to bring the cryopump to 310 K, followed by evacuation with a mechanical pump to 100 mTorr without heat or purge, then closing the roughing valve and starting the cryopump. An initial water vapor pressure of 100 mTorr does not increase the cool‐down time compared to a lower starting pressure. Tests with other gases showed that argon and nitrogen have to be pumped below 20 mTorr and hydrogen and helium have to be pumped below 4 mTorr to avoid long delays in cool down.