Other techniques

Abstract

Abstract The earlier chapters should have made obvious the importance of high vacua in reaching and maintaining low temperatures. The present chapter discusses the main types of vacuum pumps, vacuum gauges and sealing techniques. More details of their role in small and large systems-cryogenic and otherwise-can be found in the many textbooks on vacuum technology (e.g. Dushman 1962; Yarwood 1967; Holland et al. 1974; Roth 1982). At low temperatures, the cryogen itself is a source of pumping-cryopumping. However, low temperatures present another problem, namely the brittle nature of the seals which are used at normal temperatures. Many rubber gasket or rubber O-ring seals are no longer practicable for vacuum-tight assemblies at low temperatures, witness the Challenger disaster. In Section 10.3 of this chapter a brief account is given of soft-metal O-ring seals and some low-melting-point solders which are useful in making vacuumtight joints which can be cooled and can also be ‘broken’ and remade fairly readily. Some other type of vacuum seals and cements as well as the use of metal-glass seals at low temperatures are described later in the chapter.