Development of a Magnetic Refrigerator Operating Between 2K and 10K
An adiabatic demagnetization refrigerator (ADR) is under development at NASA-Ames Research Center that will operate between 2 K and 10 K and will provide 50 mW of cool ng at 2 K. Gadolinium Gallium Garnet (GGG) is selected as the refrigerant for the ADR, To minimize temperature gradients in the GGG, thick slices of GGG are sandwiched together with strips of high-purity copper in between them. The copper strips are used to exchange heat between the GGG and the 2 K and the 10 K heat switches. The heat transfer across the Cu-GGG interfaces is improved by placing thin foils of' high-purity indium at the interfaces. The heat switches employed in the ADR have no moving parts. The 10 K heat switch is a helium gas-gap heat switch; while, the 2 K heat switch is a He ll-gap heat switch. A switch is on when its gap Is filled with helium and is off' when the gap is emptied. This is accomplished with an activated carbon pump (ACP). The ACP adsorbs helium when cooled and desorbs it when heated. A superconducting magnet capable of providing 9 T at 2 K is used for the ADR cycle. A prototype of this refrigerator has been built and is currently under test. A detailed design of the ADR and preliminary test results performed on the prototype ADR will be presented.