ADR configurations and optimization for cryocooler-based operation

Because of renewed interest in low temperature refrigeration. for space missions, there has been considerable developmental work on adiabatic demagnetization refrigerators (ADR) over the last decade or so. As a result, they have expanded from single-stage systems requiring relatively low heat sink temperatures to multi-stage systems capable of rejecting heat to 5 K and higher. This capability enables the use of cryocoolers for heat sinking instead of superfluid helium - a critical step in meeting the space community's need for long-life, low temperature coolers. Since there is no intrinsic limit to an ADR's operating range, the interface temperature for a hybrid ADR/cryocooler system can be set to achieve various performance goals, such as maximizing total system efficiency or minimizing mass. In addition, a larger operating range affords greater flexibility in selecting a cryocooler. In this paper we compare the specific power of ADRs and cryocoolers to develop guidelines for optimizing total system performance, and discuss configurations and operating modes for higher temperature ADRs, along with future technology developments needed to implement them.