A Magnetic Refrigerator for Superfluid Helium Equipped with a Rotating Superconducting Magnet System

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Abstract
A rotating magnetic refrigerator based on a new concept has been designed, and a prototype has been tested. The model refrigerator uses gadolinium gallium garnet (GGG) as the working substance and realizes a Carnot cycle between about 2 K and 4.2 K. Heat switches are employed which utilize differences in the heat transfer modes of helium and are free of moving parts. By rotating a system of superconducting coils in the persistent current mode, the working substance at rest is sinusoidally magnetized and demagnetized and this effects the refrigeration cycle. At the maximum magnetic field applied to the GGG of 2.94 T and the operating frequency of 0.20 Hz (rotational speed 4 rpm), the minimum temperature obtained was 1.90 K and the useful cooling power was 1.5 W at 2.10 K.