Sorption Cryopumps
WithL. Piccirillo, G. Coppi, A. May
Pages 11

In those cryogenic applications, such as large liquid bath cryostats used to cool superconducting magnets and radio frequency cavities found in modern particle accelerators, pumping is done on the working fluid by mechanical pumps. Charcoal pumps using helium molecules are one of the important components in a sub-K sorption cooler. The sums of all the forces that are not related to an electrostatic interaction or a covalent bond are grouped together into a unique category: the van der Waals Force. This force includes three major contributors: the London Dispersion Force, the Keesom Interaction and Debye Force. The choice of an adsorbent material needs to be selected and be sized such that it is able to adsorb all the gas in the sorption cooler and at the same time it is able to create a good vacuum. This implies a reduction of the pressure on the liquid and consequentially a dropping in temperature.