cryopumps

Cryopumps are vacuum pumps that achieve very high vacuums by removing gas molecules through cryogenic condensation and adsorption on cold surfaces. They operate by cryocondensation, in which gas molecules condense on surfaces cooled to cryogenic temperatures, and by cryosorption, in which low-temperature surfaces, often lined with activated charcoal, adsorb gases. A typical cryopump uses two temperature stages: a warm stage around 70–100 K where most condensable gases such as water, oxygen, nitrogen, and neon condense, and a second, colder stage around 4–20 K that adsorbs light gases such as hydrogen and helium. Some designs employ a single stage with a cryocooler and a separate charcoal bed; others are supplied with liquid nitrogen as a coolant. Closed-cycle cryopumps use mechanical cryocoolers to reach refrigeration without liquid cryogens.

Construction and integration: Cryopumps are integrated into vacuum systems and backed by roughing pumps and turbomolecular or molecular pumps to achieve ultra-high vacuum. The cold surfaces are thermally isolated and surrounded by radiation shields. The pumping action is oil-free and contains no moving parts at the cold surface, reducing contamination and vibration.

Operation and maintenance: Gas molecules are drawn down as the chamber is cooled and the pump captures them on the cold surfaces. Once the cold surfaces become saturated, the pump is warmed (regenerated) to release trapped gases, which are then evacuated by the system. The process is repeated as needed.

Applications: Cryopumps are commonly used in semiconductor processing, surface science experiments, electron microscopy, fusion research, space simulation chambers, and other ultra-high vacuum applications where oil-free, chemically inert pumping is required.