A Rapid Turnaround Two-Stage Adiabatic Demagnetization Refrigerator for Cooling to 50 mK

Abstract

Many research and development programs require rapid access to very low temperatures (∼50 mK). For detector development, relatively large experiment volumes are also needed for tests involving integrated detectors and readout amplifiers (which may need to be stationed at a different temperature). To provide this capability in a versatile, fast turnaround system, we have constructed a two‐stage adiabatic demagnetization refrigerator (ADR) that is operated in a simple bucket‐style dewar. The ADR/cryostat is separated into two concentric inserts; the outer insert supports two 3.3 T magnets, magnet leads and magnetic shielding, and the inner one consists of a hermetic experiment volume coupled to the ADR’s salt pills and heat switches. The magnet insert remains in the dewar at all times, while the ADR insert may be inserted and removed even when the dewar is cold. The cooldown from room temperature takes less than 1.5 hours, and cycling of the ADR as little as 30 minutes. Future tests will investigate the use of neon exchange gas to accelerate cooling of the ADR and more thermally isolated components such as wiring and structural supports. Design and operation of the system are discussed.