Cold trap

In vacuum applications, a cold trap is a device that condenses all vapors except the permanent gases (hydrogen, oxygen, and nitrogen) into a liquid or solid.

[2][needs update] The most common objective is to prevent vapors being evacuated from an experiment from entering a vacuum pump where they would condense and contaminate it.

Cold traps also refer to the application of cooled surfaces or baffles to prevent oil vapours from flowing from a pump and into a chamber.

This is accomplished through the use of a coolant such as liquid nitrogen or a freezing mixture of dry ice in acetone or a similar solvent with a low melting point.

Cold traps are also used in cryopump systems to generate hard vacua by condensing the major constituents of the atmosphere (nitrogen, oxygen, carbon dioxide and water) into their liquid or solid forms.

Cold trap immersed in cold medium in Dewar flask. Some workers prefer the opposite arrangement, where vapors flow down the wall of the trap, and are sucked up the inner tube; this reduces blockage. ^{[

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