cryopumput

Cryopumput are vacuum devices that use cryogenic temperatures to capture gas molecules on cold surfaces, thereby achieving very high vacua. They typically operate with little to no moving parts, relying on surfaces cooled by liquid helium or cryocoolers to trap gases by condensation and adsorption.

The pumping mechanism works by exposing the chamber interior to extremely cold surfaces. In a two-stage design, the first stage at roughly 50–120 K condenses water vapor and other condensables on a cryogenic surface, while a second stage at around 4–20 K adsorbs or condenses light gases such as hydrogen, nitrogen, oxygen, and carbon monoxide. Helium is difficult to trap at practical cryogenic temperatures and often remains as a residual gas requiring additional pumping methods.

Operation generally requires a roughing pump to evacuate the chamber before the cryopump is activated. After achieving the desired vacuum, the cryopump can run for extended periods due to its lack of moving parts, but it requires periodic regeneration. Regeneration involves warming the cold surfaces to desorb trapped gases, which are then vented away, after which the pump is cooled again for continued use.

Cryopumput are valued for high pumping speeds for condensable gases, low vibration, chemical inertness, and suitability for ultra-high vacuum environments. They find applications in semiconductor manufacturing, surface science experiments, electron and ion beam systems, fusion research, and space simulation chambers. Limitations include poor performance for non-condensable gases such as helium, reliance on continuous cooling, and the need for regular regeneration and cryogenic maintenance. Safety considerations involve handling cryogens, proper ventilation, and careful venting during regeneration.