Magnetic Refrigeration

Magnetic refrigeration has been used chiefly as a cooling method to obtain temperatures below 1 K. During the past ten years, however, the technology has been developed also for refrigeration applications at temperatures above 1 K. The former type of magnetic refrigerator utilizes an adiabatic one-shot process to approach zero Kelvin as a purely scientific goal. For application at temperatures higher than 1 K, a continuously cycling magnetic refrigerator with reasonable refrigeration capacity is employed. This latter type of refrigerator can be utilized in actual engineering applications, such as cooling sensitive electronics and optical devices on board spacecraft.

Two important research topics are required to support any successful magnetic refrigerator development program: magnetothermodynamic analysis, and low-loss superconducting magnet development. The former is usually done by computer simulation, in parallel with the overall conceptual design. One calculates the real thermodynamic properties of the magnetic refrigerant and performs cycle analysis. The latter topic is the more practical task, relying largely on empirical knowledge.

The development of a pulsed superconducting magnet was one of the PSFC's important R&D areas, and intensive work has been performed to characterize proper superconducting wire for various types of magnet. A Nb3Sn low loss ac superconducting magnet is an excellent choice for magnetic refrigeration. The operation of such a magnet at temperatures higher than 4.2 K using, a cryocooler, will also increase the overall thermodynamic efficiency of a magnetic refrigeration system.

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