Preamble

In this chapter we shall describe the application of some of the ideas presented in Chapters 1 and 2 to the dilution refrigerator. This device has been of crucial importance for the development of low temperature physics since the mid-sixties when it was first demonstrated (Hall et al. (1966)) to be a practical proposition. Several sources have provided the material for this chapter, and may be consulted by the reader wishing to pursue the matter in great depth. These sources importantly include two research monographs by Lounasmaa (1974) and by Betts (1976), both of which need to be updated, a much-used conference review article by Frossati (1978) and its sequel by Vermeulen and Frossati (1987), and a privately circulated manual by Sagan (1981). There are also useful articles by Wheatley et al (1968) and (1971), Niinikoski (1976), Frossati et al (1977), Lounasmaa (1979) and Bradley et al (1982). It would I think be generally acknowledged that Frossati is the master in this field, and his article is the main inspiration for this chapter. The aim is briefly to cover the functions of the various components, and to offer a guide to design considerations and to the sort of performance which can be achieved at present. In the early days dilution refrigerators were homemade but most users now buy them commercially in much the same way as consumers buy domestic refrigerators, though at considerably greater expense. The main supplier at present is the Oxford Instrument Company based in the UK.

Evaporation cooling

It is useful to begin by having in mind a simple image of an evaporation cooler as shown in Figure 3.1.