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The ‪#‎cryopump‬ is a high vacuum pump that is based on the adsorption of gas on cold surfaces. The cooler the surface – the better the pumping! For that purpose liquid helium is often used for cooling the system parts as it is extremely cold, having a temperature only four degrees above absolute zero. The pumping is done in multiple stages, where each stage has a different temperature. The „warmest“ part is the first stage, that has a temperature of 100 degrees Kelvin (or lower) and that causes water to condensate on it. During the ‪#‎condensation‬ of water also some other gases may also be trapped under the water and that process is called ‪#‎cryotrapping‬. However, in order to effectively pump gases such as nitrogen, even colder surfaces (less than 17 degrees Kelvin) are required. In this stage the metal may also be coated with porous activated charcoal and that allows to adsorb even smaller gas molecules such as helium and even hydrogen (this is called ‪#‎cryosorption‬ ). So basically the pumping of gases with this ‪#‎vacuumpump‬ is based on three processes: condensation, cryotrapping and cryosorption.

Titanium Sublimation Pump

The titanium sublimation pump is a vacuum pump used as a part of vacuum systems in order to briefly improve the level of ‪#‎vacuum‬. The working principle is relatively simple. A pulsing current passes through a titanium filament, causing it to sublimate (goes directly from solid phase to gas phase). The fresh titanium chemically reacts with gas in the vacuum chamber, creating a solid product that deposits on the chamber walls. As the walls are also coated with highly reactive freshly deposited titanium, they may also chemically bind gas molecules that interact with them. Some gases may not chemically bind with titanium but can still be physically trapped under the titanium atoms on the chambers walls.

Vacuum Systems and Technologies

Vacuum can be understood as space from where matter (for example air) has been removed. It naturally exists in outer space but for certain applications, like materials characterization techniques, it needs to be achieved artificially. The desired level of vacuum is obtained with the help of a suitable vacuum pump. For example low vacuum (low quality vacuum with higher pressure) can be generated with a diffusion pump, scroll compressor pump, rotary vane pump, diaphragm pump or a sorption pump. High vacuum (high quality vacuum with very low pressures) however, can be obtained with high vacuum pumps such as the turbomolecular pump, ion pump, titanium sublimation pump and cryopump. The level of vacuum is measured with devices called vacuum gauges (vacuum meters) like the thermocouple gauge, pirani gauge, penning ionization gauge and the quadrupole mass spectrometer (analyzer). The working principle of vacuum pumps and vacuum gauges is explained with 3D animations in the video lecture above.