Magnetostrictive Heat Switch for Cryogenic Use

A magnetostrictively actuated heat switch has been proposed for use in a variety of cryogenic equipment, including adiabatic-demagnetization refrigerators, calorimeters, and coolers for high-performance infrared cameras. Heretofore, the heat switches in such equipment have generally been of two types: gas-gap and externally mechanically actuated. The gas-gap switches are limited to long cycle times and tend to exhibit both poor isolation in their "open" states and low "closed"/"open" heat-transfer ratios. In the case of externally mechanically actuated switches, the mechanical connections between the switches and the outside environment are heat-conduction paths, along which heat leaks into the affected cryogenic chambers. In contrast, the proposed magnetostrictively actuated switch would feature short cycle times, low heat leakage, high isolation in the "open" state, and a high "closed"/"open" ratio.