A Magnetic Refrigerator for Cooling at 2 K

NASA requires cooling of detectors for space telescopes. Detector temperatures as low as 0.05 K are being specified for a number of missions. A number of physics experiments proposed on the International Space Station require very low temperatures as well. Thus, NASA has identified a dilution refrigerator (DR) as a new technology requirement for its Fundamental Physics program.For a DR to operate it requires pre-cooling at 2K. Other than stored He II an ADR is the only suitable technique for achieving 2K in space. The ADR can serve to pre-cool a DR or a low-temperature ADR stage to achieve very low temperatures. It can also be integrated into a He II storage dewar to eliminate boil-off. This will reduce size and increase lifetime of such a system making long-duration experiments feasible.An ADR is designed to provide cooling at 2K. Cycling the magnetic refrigerant it is necessary to connect or isolate the refrigerant to/from the heat source and the heat sink. This is accomplished by employing novel heat switches. The efficiency is greatly affected by the performances of the heat switches. In the design the on and off conductances and the switching times of the heat switches are optimized to achieve a high efficiency.