ADIABATIC DEMAGNETIZATION COOLER FOR INFRARED DETECTOR

An adiabatic demagnetization cooler with an indirectly cooled superconducting magnet was fabricated for an infrared detector. The operating temperature was designed to be 0.2 K. The temperature of the sensor, which replaced the infrared detector, was successfully maintained at 0.200-0.205 K for 7 h by active magnetic field control, using single crystal chromic potassium sulphate as a magnetic working substance. Using manganese ammonium sulphate, a temperature below 0.300 K was maintained for over 12 h, although the lowest sensor temperature was 0.237 K. Yttrium aluminium garnet doped with the magnetic impurity neodymium ion (Nd3+) was also tested, it being a substitute for paramagnetic salts from the viewpoint of easy processing and handling. Using this garnet a temperature of 0.203 K could be obtained, though this could only be maintained for 6 min. A proposal for improvement in the garnet cooling capacity has been made. © 1990.