An adiabatic demagnetization refrigerator for SIRTF

An adiabatic demagnetization refrigerator (ADR) has been proposed to cool bolometric infrared detectors on the multiband imaging photometer of the Space Infrared Telescope Facility (SIRTF). One such refrigerator has been built which uses a ferric ammonium alum salt pill suspended by nylon threads in a 3-T solenoid. The resonant modes of this suspension are above 100 Hz. The heat leak to the salt pill is <0.5 μW. The system has a hold time at 0.1 K of >12 h. The cold stage temperature is regulated with a feedback loop that controls the magnetic field. A second, similar refrigerator is being built at a SIRTF prototype to fly on a balloon-borne telescope. It will use a ferromagnetic shield. The possibility of using a high-T_c solenoid-actuated heat switch is also discussed