Dilution refrigerator technology

This review discusses theoretical and practical developments concerning the He3He4 dilution refrigerator. Properties of He3He4 solutions are briefly discussed in terms of the weakly interacting Fermi-Dirac gas model and re-used to calculate the behaviour of dilution refrigerators. The thermodynamic behaviour of the dilution process is first discussed, and then an analysis of various types of heat exchangers is presented. The use of nearly optimum heat exchangers, designed by the method outlined here, can significantly reduce the liquid volumes required and/or reduce the low temperature limit of the continuous dilution refrigerator. With smaller liquid volumes, the refrigerator can be cooled down and can reach thermal equilibrium more rapidly. Discussions of various practical considerations and recent developments in hardware are also included. Some suggestions for future work and speculations on trends are presented.