A three-stage helium sorption refrigerator for cooling of infrared detectors to 280 mK

We review some of the applications of submillimetre instruments for astrono my and Earth atmospheric sciences where helium sorption refrigerators have been used. We describe a three-stage helium refrigerator which uses a He-4- He-3 double-stage refrigerator to precool and intercept the parasitic heatl oad on a final He-3 single-stage refrigerator. This multi-stage configurati on permits operation of the refrigerator system without externally pumping on a He-4 bath. This results in simpler integration with the instrument and allows scientific observations to be more easily made. We have achieved a base temperature of 234 mK for a hold time of 20.4 h. The heat Lift at 280 mK is 15 muW. (C) 2001 Elsevier Science Ltd. All rights reserved.