Gettering in cryogenic applications

Abstract

Metallic cryogenic Dewars and pipes, used for storage and transportation of cold fluids such as liquid N2 or He, usually have a vacuum jacket as a thermal insulator. In this case, vacuum has to be maintained in a range of 10−1 Pa or lower. Nonevaporable getters are often used for this purpose. They are particularly useful for sorbing H2 which is released by the warmer walls or by the multilayer insulation; H2 is neither cryocondensed by the cold surfaces nor sorbed by the molecular sieves which may be used to physisorb other gaseous species. The working temperature of the getters may range from room temperature down to the cryogenic fluid temperature. The getter material here considered, and which appears to be adequate for these applications, is the Zr–V–Fe nonevaporable getter alloy. Its sorption characteristics (particularly for H2) are studied both at room temperature and in a cryogenic fluid environment. The behavior of a gettered Dewar jacket is finally studied and discussed.