The sorption pump is a vacuum pump that creates a vacuum by adsorbing molecules on a very porous material like molecular sieve which is cooled by a cryogen, typically liquid nitrogen. The ultimate pressure is about 10-2 mbar. With special techniques this can be lowered till 10-7 mbar. The main advantages are the absence of oil or other contaminants, low cost and vibration free operation because there are no moving parts. The main disadvantages are that it cannot operate continuously and cannot effectively pump hydrogen, helium and neon, all gases with lower condensation temperature than liquid nitrogen. The main application is as a roughing pump for a sputter-ion pump in ultra-high vacuum experiments, for example in surface physics.
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