A Four-Stage Continuous ADR for Space Missions

The cryogenics group at NASA-Goddard has provided adiabatic demagnetization refrigerators (ADRs) for cooling detectors to sub-Kelvin temperatures in space. These ADRs were single-shot devices that produced cooling at 0.05 K for tens of hours before needing to be recycled. Our group also developed a four-stage laboratory ADR system which holds one stage continuously at 0.05K, or colder, while using the other stages to pump heat from the continuous stage up to a heat sink near 4K. This continuous ADR (CADR) provides a useful cooling power that is more than 10 times greater at 0.050 K than what was required by the single-shot space systems. Over the past several years, this system was updated so that it can withstand the rigors of a launch into space. We describe this development process and report its final results.