Kryopumpen

Kryopumpen, or cryopump, is a vacuum pump that achieves ultra-high vacuum by removing gas molecules through condensation and adsorption on cryogenic surfaces. The term is used to describe devices in vacuum systems that rely on very low temperatures to trap gases, providing oil-free pumping and high purity vacuum conditions.

How it works: Gas molecules from the chamber are captured by cold surfaces inside the pump, which are cooled by cryogens or cryocoolers. Condensable gases such as water, nitrogen, and oxygen condense on the cold surfaces, while permanent gases like hydrogen and helium are predominantly trapped by adsorption on activated charcoal at very low temperatures. Many cryopumps employ multiple cooling stages and radiation shields to minimize heat load and increase efficiency, often in combination with a roughing pump or turbomolecular pump upstream to maintain gas flow.

Construction and variants: A cryopump typically consists of a cold head or chamber connected to a cryogenic reservoir or a closed-cycle cooler. Some designs use a liquid nitrogen shield around 77 K and a lower-temperature stage for enhanced adsorption of light gases. Modern systems frequently use cryocoolers that do not require liquid helium, and they incorporate regeneration cycles that warm the cold surfaces to release trapped gases for venting or recycling.

Advantages and limitations: Cryopumps are oil-free and can deliver very clean, stable ultra-high vacuum with high pumping speeds for many common gases. They require refrigeration power and periodic regeneration, and they are less effective for certain light gases under specific conditions. They are typically used as part of larger vacuum installations that include other pumping technologies.

Applications: Used in semiconductor fabrication, surface science and thin-film research, mass spectrometry, cryogenic experiments, and accelerator or fusion research, where sustained ultra-high vacuum is essential for measurements and processes.