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Continuous Magnetic Refrigerators for Cooling in the 0.05 to 10 K Range: Progress and Future DevelopmentLow temperature refrigeration is an increasingly vital technology for NASA s Space Science program since most detectors being developed for x-ray, IR and sub-millimeter missions must be cooled to below 100 mK in order to meet the requirements for energy and spatial resolution. For space applications, magnetic refrigeration has an inherent advantage over alternative techniques because it does not depend on gravity. Adiabatic demagnetization refrigerators, or ADRs, are relatively simple, solid state devices. The basic elements are a magnetocaloric refrigerant (usually an encapsulated paramagnetic salt) located in the bore of a superconducting magne$, and a heat switch linking the salt to a heat sink. The alignment of magnetic spins with the magnetic field causes the refrigerant to warm as the magnetic field increases and cool as the field decreases. Thus the simple process of magnetizing the refrigerant to high field with the heat switch closed, then demagnetizing it with the heat switch open allows one to obtain temperatures well below 100 mK using a heat sink as warm as 4.2 K. The refrigerant can maintain a low temperature for a length of time depending on the applied and parasitic heat loads, its mass, and the initial magnetic field strength. Typically ADRs are designed for 12-24 hours of hold time, after which they must be warmed up and recycled. The drawback to single-shot ADRs is that the cooling power per unit mass is relatively low. Refrigerants that are suitable for low temperature operation necessarily have low magnetic ion density, and therefore low entropy density. Since ADRs store entropy, systems with even modest cooling powers (a few microwatts) at temperatures below 100 mK tend to be massive, averaging 10-15 kg.
Document ID
20040081116
Acquisition Source
Goddard Space Flight Center
Document Type
Conference Paper
Authors
Shirron, Peter
(NASA Goddard Space Flight Center Greenbelt, MD, United States)
DiPirro, Michael
(NASA Goddard Space Flight Center Greenbelt, MD, United States)
Canavan, Edgar
(NASA Goddard Space Flight Center Greenbelt, MD, United States)
Tuttle, James
(NASA Goddard Space Flight Center Greenbelt, MD, United States)
King, Todd
(NASA Goddard Space Flight Center Greenbelt, MD, United States)
Numazawa, Takenori
(National Inst. for Materials Science Tsukuba, Japan)
Date Acquired
August 21, 2013
Publication Date
October 8, 2003
Subject Category
General
Meeting Information
Meeting: Japanese Cryogenics Conference
Location: Tokyo
Country: Japan
Start Date: December 3, 2003
End Date: December 5, 2003
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.

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