A regenerative magnetic refrigerator operating between 4.2 K and 1.8 K

Abstract

This paper describes the development of a 100 mW tandem regenerative magnetic refrigerator in the temperature range 1.8 K∼4.2 K. The inherent sources of irreversibility in regenerative magnetic refrigerators, i.e. helium entrainment, heat capacity imbalance between magnetic refrigerant and heat transport gas, and dead volume effect, have been minimized by the design optimization of the system components. The magnetic system of the tandem refrigerator has two virturally identicial units, each consisting of a GGG (Gadolinium Gallium Garnet; Gd3Ga5O12) magnetic core, a superconducting magnetic, and a warm‐ and a cold‐end heat exchanger. These components are united by a cryogenic displacer which shuttles 40‐torr He3 gas between the two units. A sub‐atmospheric He3 gas, rather than atmospheric He4, was chosen as the heat transport medium chiefly to reduce the adverse effect of helium entrainment in the magnetic cores and to avoid undesirable superfluidity. Because of experimental difficulties, the prototype was operated with parameters that were different from those selected in the design phase. The experimental result shows that the net refrigeration rate was 12 mW at 1.8 K.