The double ADR was a novel two-stage ADR that I worked on during my Ph.D. It was designed as a pre-prototype for future ADR sytems intended for use on astronomical satellites, and therefore the mass, volume and power consumption had to be minimised. Another important requirement was to minimise the magnetic field used, so that it could be shielded and would not interefere with other systems on the satellite. These requirements were met in part through several novel design features, and in part through dividing the cooling effort across two stages, so that the field used on each stage could be kept below 4 Teslas. The double ADR was also designed to operate from a 4.2K thermal bath provided by a mechanical cooler, allowing completely cryogen-free operation and so greatly increasing the lifetime of a satellite mission.
The double ADR was a flexible system with many different modes of operation. The simplest possible mode used each stage in series to achieve the lowest possible temperature, with dysprosium gallium garnet (DGG) as the first stage refrigerant and cerium magnesium nitrate (CMN) as the second stage refrigerant. The graph below shows a simulation of this mode, using fields of 3.5T on the first stage and 1.5T on the second. The predicted base temperature in this mode was ~8mK.