kryopumppu

A kryopumppu, or cryopump, is a type of vacuum pump that utilizes extremely low temperatures to capture gas molecules from a vacuum chamber. Unlike other vacuum pumps that expel gases, cryopumps condense or adsorb them onto cold surfaces. This process is particularly effective for removing high-boiling-point gases and achieving ultra-high vacuum conditions.

The primary components of a cryopump typically include a cold stage, often cooled by a cryocooler such as a Gifford-McMahon (GM) cryocooler. The first stage is usually cooled to around 50-80 Kelvin and is equipped with baffles to intercept infrared radiation. The second stage is cooled to a much lower temperature, typically 10-20 Kelvin, and is where most of the gas is captured. This second stage often incorporates activated charcoal or other adsorbent materials bonded to its surface, which significantly increases the pumping speed for various gases.

When gas molecules enter the cryopump, they collide with the cold surfaces. If their temperature is below their condensation point at the prevailing pressure, they will liquefy and freeze onto the surface. For gases with very low boiling points, such as hydrogen, helium, and neon, the adsorbent material on the second stage plays a crucial role. These adsorbents can capture gas molecules through van der Waals forces, even when the gas is far below its condensation temperature.

Cryopumps are widely used in scientific and industrial applications where ultra-high vacuum is required. This includes semiconductor manufacturing (e.g., in deposition and etching processes), particle accelerators, space simulation chambers, and scientific research involving high vacuum environments. They are known for their high pumping speeds for many gases and for their ability to achieve very low ultimate pressures, free of oil contamination often associated with other vacuum pump types. Regeneration, the process of warming the pump to release captured gases and restore its pumping capacity, is a necessary maintenance procedure for cryopumps.