Continuous magnetic refrigeration in the superfluid helium range

An experimental prototype magnetic refrigerator based on the well known adiabatic demagnetization principle is described. A continuous process is employed in which gadolinium garnet follows successive magnetization-demagnetization cycles between a hot liquid helium source at 4.2K and a cold superfluid helium source at T<= 2.16K. The performance achieved with the first version is as follows: - limiting temperature at zero utilizable power: 1.32K; - utilizable power of 1.2W at 1.8K with an efficiency of 45%. In a second version, it was possible to increase the efficiency to 64% for a utilizable power of 0.9W at 2.1K. Same general remarks are made on the possibility of extrapolating to a 300W refrigerator operating at 1.8K, on a continuous rotating magnetic refrigerator of a different design, and on efficiency comparisons between gas and magnetic refrigerators