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Model 16RD-ADR Two Stage Adiabatic Demagnetization Refrigerator System

The system consists of the following components:

• Model 16RD nitrogen shielded, superinsulated liquid helium cryostat containing an adiabatic demagnetization refrigerator (ADR) system. The nitrogen reservoir has a nominal 7.5-liter capacity and a hold time (in the upright position) of ~36 hours. The helium reservoir has a nominal 8.5-liter capacity and a hold time of ~55 hours (in the upright position). This base hold time includes the heat load due to the built in magnet leads and the wiring for thermometry and diagnostics.
• A two stage ADR system with a gadolinium-gallium garnet (GGG) crystal and a ferric ammonium alum (FAA) salt pill. Each pill has its own ultra low thermal conducting support structure isolating it from the helium reservoir (GGG pill) and the intermediate stage (FAA pill). The two stages operate at a temperature of ~1 K and 50 – 100 mK without requiring any pumping on the main helium reservoir. Typical ADR hold time is over two days below 100 mK.
• A mechanical thermal heat switch assembly for attaching and detaching the two stages of the ADR during initial cool down, and during its magnetization and demagnetization cycles.
• Two ruthenium oxide thermometers with appropriate heat sunk wiring at the various intermediate stages to monitor the temperature of the two stages of the ADR. The two thermometers are supplied with a standard calibration data between 50 mK and 20 K.
• A 4 Tesla conductively cooled multi-filamentary Niobium-Titanium superconducting magnet surrounding the GGG and FAA pills. The magnet is wired with an optimized arrangement of regular and high temperature superconducting leads, and is provided with voltage taps and two standard thermometers to monitor its cool down and operating temperature. The magnet reaches its rated field of 4 Tesla at a nominal 10 amperes.
• A high permeability magnetic shield surrounding the magnet and the two pills, to reduce the stray magnetic field in the vicinity of the cold stages.
• Complete wiring, interfacing and testing of all components, including the ADR pills, magnet and thermometry. This includes a final test of the complete system with liquid helium, to ensure precise dewar and ADR hold time and operation.

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