DESIGN AND CONSTRUCTION OF A STATIC MAGNETIC REFRIGERATOR OPERATING BETWEEN 1.8-K AND 4.5-K

Following pioneer work a decade ago at CEA/CEN-Grenoble, France we hav e designed and constructed a static magnetic refrigerator with a capac ity of about 20 W, operating on a quasi-Carnot cycle between 1.8 and 4 .5 K. The active core, which contains 10.1 kg of single-crystal gadoli nium-gallium garnet (GGG), is magnetized and demagnetized by a 3.5 T p ulsed-field, low-loss superconducting magnet operating at 4.5 K. Therm al switching to the cold and warm sources is produced by alternatively flushing the core with liquid helium from the 1.8 and 4.5 K baths, by means of alumina-piston and -cylinder displacer pumps. Precise modell ing of thermodynamic properties of GGG, as well as detailed analysis o f the different sources of irreversibility, allow to estimate the avai lable refrigeration power and optimize the operating cycle.