Adsorption is the physical mechanism by which a gas can be trapped on a surface. For a given material, the quantity of gas adsorbed is a function of the temperature and by the pressure, it increases when the temperature decreases and/or the pressure increases.
Thus while varying the temperature it is possible to carry out a compression or a relaxation (pumping). This effect can then be used to design thermal compressors intended to feed, for example, a loop Joule Thomson, or to carry out a cryopompe making it possible to lower the pressure on a bath and thus to decrease its temperature. Moreover, this capacity to modify the pressure by varying the temperature makes it possible to design thermal switches with extremely effective gases of exchange.
The principal interest of this technology is its total absence of parts moving. On the other hand, need for cycling components in temperature the reserve at the low even very low temperatures, where the low specific heats make it possible to obtain reasonable thermodynamic effectiveness. ECA-SBT however worked on systems functioning at the temperatures of liquid nitrogen or even at temperatures close to 150 K. It is thus for the range of the temperatures relating to liquid helium (normal "4" or isotope "3" [ 0.2 K - 5 K ]) that this technique of cooling shows all its benefit and its capacities.
The guiding principle consists in condensing gas, then to decrease its vapor pressure to lower its temperature. The management of gas is ensured by a pump adsorption and the control of the heat gradients by thermal switches (with adsorption).
Multiple systems specific to the grounds applications were developed at ECA-SBT, monoétagé 3He or 4He, two-stage 4He/3He or 3He/3He, interruptory thermics, and except for specific achievements the majority were transferred to Liquid air. Concerning space applications ECA-SBT developed and qualified with the European Space Agency of the thermal switches and cryorefrigerator 3He and 4He.
Within the framework of mission HERSCHEL ECA-SBT has the responsibility for the supply of the cryoréfrigérateurs with adsorption of flight of two of the three scientific instruments, WHORL (Spectral and Photometric Imaging Receiver) and PACS (Photo-conductor Array Camera & Spectrometer). Indeed, the detectors bolometric of these instruments function at temperatures close to 300 mK, and make it possible to carry out observations in the submillimeter infra-red range.