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The term "roughing pump" derives from the vacuum range it works in, "rough vacuum", above 1x10 −3 torr (0.1 Pa). Pumps that operate in the high vacuum ranges typically don't operate, or only operate inefficiently, at atmospheric pressures , whereas pumps that work efficiently at atmospheric pressure usually cannot produce a vacuum lower than ...
Vacuum techniques vary depending on the desired vacuum pressure to be achieved. For a "rough" vacuum, over 100 Pascals pressure, conventional methods of analysis, materials, pumps and measuring instruments can be used, whereas ultrahigh vacuum systems use specialized equipment to achieve pressures below one-millionth of one Pascal.
Typically, this backing pressure is below 0.1 mbar and commonly about 0.01 mbar. The backing pressure is rarely below 10 −3 mbar (mean free path ≈ 70 mm) because the flow resistance of the vacuum pipe between the turbopump and the roughing pump becomes significant. The turbomolecular pump can be a very versatile pump.
There is no single vacuum pump that can operate all the way from atmospheric pressure to ultra-high vacuum. Instead, a series of different pumps is used, according to the appropriate pressure range for each pump. In the first stage, a roughing pump clears most of the gas from the chamber. This is followed by one or more vacuum pumps that ...
Sorption pumps are a type of cryopump that is often used as roughing pumps to reduce pressures from the range of atmospheric to on the order of 0.1 Pa (10 −3 Torr), while lower pressures are achieved using a finishing pump (see vacuum).
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.
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