ADIABATIC DEMAGNITIZATION REFRIGERATOR

ADIABATIC DEMAGNITIZATION REFRIGERATOR

INTRODUCTION:

The word CRYOGENIC means literally the production of icy cold: however the term is used today synonym for low temperatures. The point on temperature scale at which refrigeration in the ordinary sense of the term ends and cryogenics begins is not sharply defined. However the works National Bureau of Standards at Boulder, Colorado [1] have chosen to consider field of cryogenics as that involving temperatures below - 1500C. This is the logical dividing because normal boiling points of so called permanent gases such as He, H, O2, N lie below -1500C Cryogenics finds its advanced applications in the fields like space, medical, manufacturing etc. A device Adiabatic Demagnetization Refrigerator (ADR) [2] is one of such applications of cryogenics and used for producing temperatures well below 1K (up to 65mK i.e. 0.065OC above absolute zero). It’s a type of cryocooler used for cooling the infrared detectors (sensors) and other electronic systems used in spacecraft which could not operate at high temperatures. The Adiabatic Demagnetization Refrigerator (ADR) is a magnetic cooling system that has been used routinely in the laboratory for cooling to temperatures below the temperature of liquid helium. Astronomers are now developing sensors for x-ray and infrared astronomy which will operate in this temperature range. Since these sensors are more sensitive than their higher temperature predecessors, cryogenic engineers are now hard at work on the systems to cool them in orbit.

An ADR for space use is under development at. The NASA's Goddard Space Flight Center (GSFC) [3] The

ADR developed by Goddard is a heat pump that operates between liquid helium temperature and very low temperatures. Goddard developed an ADR for the X-Ray Spectrometer (XRS) to cool detectors to 0.065 Kelvin (65 mK). Ground-based ADRs have been constructed that have reached approximately 2 mK. An ADR was chosen for space instead of a dilution refrigerator because it does not require gravity and because it is exceedingly efficient. The ADR for the X-Ray Spectrometer has an efficiency of approximately 50% of Carnot. This efficiency is necessary for space-based systems to allow the liquid helium dewar to operate for extended periods of time on orbit.

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