A cryopump is a vacuum pump that traps gases and vapours by condensing them on a cold surface. They are only effective on some gases, depending on the freezing and boiling points of the gas relative to the cryopump's temperature. They are sometimes used to block particular contaminents, for example in front of a diffusion pump to trap backstreaming oil, or in front of a McLeod gauge to keep out water. In this function, they are called a cryotrap or cold trap, even though the physical mechanism is the same as for a cryopump. Cryotrapping can also refer to a somewhat different effect, where molecules will increase their residence time on a cold surface without actually freezing. There is a delay between the molecule impinging on the surface and rebounding from it. Kinetic energy will have been lost, the molecules become sluggish. For example, hydrogen will not condense at 8 Kelvin, but it can be cryotrapped. This effectively traps molecules for an extended period and thereby remove them from the vacuum environment just like cryopumping. The Roots blower is one example of a vacuum pump A vacuum pump is a pump that removes gas molecules from a sealed volume in order to leave behind a partial vacuum. ... This article does not cite any references or sources. ... Vapor (US English) or vapour (British English) is the gaseous state of matter. ... Diffusion pumps are a type of vacuum pump designed to achieve better vacuum pressures than possible by use of mechanical pumps alone. ... A McLeod gauge is a scientific instrument to measure very low pressures, down to 10-7 Torr. ... General Name, Symbol, Number hydrogen, H, 1 Chemical series nonmetals Group, Period, Block 1, 1, s Appearance colorless Atomic mass 1. ... The kelvin (symbol: K) is a unit increment of temperature and is one of the seven SI base units. ...

Cryopumps are commonly cooled by dry ice or liquid nitrogen, or stand-alone versions may include a built-in cryocooler. Baffles are often attached to the cold head to expand the surface area available for condensation, but they also increase the radiative heat uptake of the cryopump. Over time, the surface eventually saturates with condensate and the pumping speed gradually drops to zero. It will hold the trapped gases as long as it remains cold, but it will not condense fresh gases from leaks or backstreaming until it is regenerated. Saturation happens very quickly in low vacuums, so cryopumps are usually only used in high or ultrahigh vacuum systems. Cryocoolers are the devices used to reach cryogenic temperatures. ...

Regeneration of a cryopump is the process of evaporating the trapped gases. This can be done at room temperature and pressure, or the process can be made more complete by exposure to vacuum and faster by elevated temperatures. Best practice is to heat the whole chamber under vacuum to the highest temperature allowed by the materials, allow time for outgassing products to be exhausted by the mechanical pumps, and then cool and use the cryopump without breaking the vacuum. Outgassing (sometimes called Offgassing, particularly when in reference to indoor air quality) is the slow release of a gas that was trapped, frozen, absorbed or adsorbed in some material. ...

Some cryopumps have multiple stages at various low temperatures, with the outer stages shielding the coldest inner stages. The outer stages condense high boiling point gases such as water and oil, thus saving the surface area and refrigeration capacity of the inner stages for lower boiling point gases such as nitrogen.

Cryopumps are often combined with sorption pumps by coating the cold head with highly adsorbing materials such as activated charcoal or a zeolite. As the sorbent saturates, the effectiveness of a sorption pump decreases, but can be recharged by heating the zeolite material (preferably under conditions of low pressure) to outgas it. The breakdown temperature of the zeolite material's porous structure may limit the temperature that can be used for regeneration. The Sorption pump is a kind of pump used in ultra high vacuum experiments, for example in surface physics in order to obtain low pressures so that experiments can take place. ... Activated carbon (also called activated charcoal) is the more general term which includes material mostly derived from charcoal. ... Zeolite The micro-porous molecular structure of a zeolite, ZSM-5 Zeolites (Greek, zein, to boil; lithos, a stone) are minerals that have a micro-porous structure. ... Sorbent material is similar to molecular sieve material. ... Outgassing (sometimes called Offgassing, particularly when in reference to indoor air quality) is the slow release of a gas that was trapped, frozen, absorbed or adsorbed in some material. ...

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 pascal (symbol: Pa) is the SI derived unit of pressure or stress (also: Youngs modulus and tensile strength). ... For the standard botanical author abbreviation Torr. ... Look up Vacuum in Wiktionary, the free dictionary. ...

References

• Van Atta, C. M.; M. Hablanian [1990] (1991). "Vacuums and Vacuum Technology", in Ed. by Rita G. Lerner and George L. Trigg: Encyclopedia of Physics, 2nd edition, New York: VCH Publisher, 1330-1334. ISBN 0-89573-752-3. 
• Strong, John (1938). Procedures in Experimental Physics. Bradley, IL: Lindsay Publications. , Chapter 3