Cryogenic Pumps

Summary

Cryogenic pumping involves capturing molecules on a cooled surface by weak van der Waals or dispersion forces. Cryopumps are used in a wide range of applications and in many forms. In this chapter, the authors review the mechanisms of cryocondensation and cryosorption on which all cryogenic pumping is based. They discuss pumping speed, ultimate pressure and saturation effects, refrigeration techniques, and pump characteristics. Cryogenic pumping surfaces are cooled either by direct contact with liquid cryogens, or by gases in an expansion cooler. The authors also discuss the speed–pressure characteristics of some ideal pumping surfaces. Liquid cryogen pumps must be individually designed to meet the diverse requirements of applications ranging from small analytical and molecular beam epitaxy systems to very large particle beamlines and chambers for testing space modules.