Experimental research on a high efficiency adiabatic demagnetization refrigerator

Adiabatic demagnetization refrigerators are being extensively applied among ultra-low temperature refrigeration technologies. There is merely rare literature about double-stage adiabatic demagnetization refrigerator, which pays more attention to the overall performance. Details were not sufficiently studied of the double-stage adiabatic demagnetization refrigerators. An adiabatic demagnetization refrigerator prototype was established and researches were carried out with experimental study. For its first stage, with the working temperature of 1 K, the relative Carnot efficiency of 85 % was obtained when the heat released temperature was 3.2 K, meanwhile the net cooling power was 0.75 mW. The relative Carnot efficiency can be improved by reducing the heat released temperature from 3.5 K to 3.2 K. The effect of demagnetization ramp rate on the first stage's cooling temperature was studied with an initial temperature of 2.7 K and maximum magnetic field of 4 T. The minimum cooling temperature of the first stage was 327 mK with a ramp rate of 8 mT/s. With the increase of the demagnetization ramp rate, the minimum temperatures were similar for the first stage, while the demagnetization time decreased from 2000 s to 500 s. The maximum cooling power and cooling capacity of the first stage were 1087 μW@1 K and 3.53 J@1 K respectively. For the double-stage adiabatic demagnetization refrigerator, the minimum cooling temperature was 63 mK, and the holding time was 3 h 40 min@100 mK without extra heat load. The temperature RMSE of the double-stage adiabatic demagnetization refrigerator was 15.5 μK@100 mK in 1 h. This refrigerator realized cooling below 100 mK based on a 4 K range heat sink, which can afford cooling the application loads down directly or play a role of pre-cooling platform for lower temperature stage.