Long-Term Performance of 4 K Gifford-McMahon Refrigerators on the Bima Array

  • R. L. Plambeck
Part of the Advances in Cryogenic Engineering book series (ACRE, volume 43)


Eight radio telescopes in the Berkeley-Illinois-Maryland Array (BIMA) are outfitted with 4 K Gifford-McMahon refrigerators. The refrigerators cool superconducting detectors (SIS mixers) on the radio receivers; the heat load at 4 K is 10 to 20 mW. The refrigerators were constructed by welding third stages onto standard CTI model 1020 cryocoolers; Er3Ni or ErNi spheres are used as the low temperature regenerators. The refrigerators are operated almost continuously; one has been in service for 4 years. Maintenance consists of disassembling the cold heads every 1 to 2 years to clean out water and dust.

On the telescopes the refrigerators’ third stage temperatures range from 2.7 to ~5 K. Often these temperatures are stable within ± 0.1 K for weeks, even while the refrigerators are tipped from 0 to 90 degrees as the telescopes track radio sources. Sometimes, however, the temperature creeps up by > 1 K over a period of days or weeks, then jumps back to its original value following a power interruption or “defrost” cycle. Contaminants within the cold head may possibly cause this behavior. With active temperature regulation, the SIS mixer temperatures can be stabilized to ±0.01 K despite the refrigerator fluctuations.


Radio Telescope Heater Power Stage Temperature Optimum Bias Mixer Block 
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Copyright information

© Springer Science+Business Media New York 1998

Authors and Affiliations

  • R. L. Plambeck
    • 1
  1. 1.Radio Astronomy LabUniversity of CaliforniaBerkeleyUSA

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