Proposed designs for a 'dry' dilution refrigerator with a 1K condenser

Recent development of “dry” dilution refrigerators has used mechanical cryocoolers and Joule–Thomson expansion stages to cool and liquefy the circulating ^3He. While this approach has been highly successful, we propose three alternative designs that use independently-cooled condensers. In the first, the circulating helium is precooled by a mechanical cooler, and liquified by self-contained ^4He sorption coolers. In the second, the helium is liquefied by a closed-cycle, continuous flow ^4He refrigerator operating from a room temperature pump. Finally, the third scheme uses a separate ^4He Joule–Thomson stage to cool the ^3He condenser. The condensers in all these schemes are analogous to the “1-K pot” in a conventional dilution refrigerator. Such an approach would be advantageous in certain applications, such as instrumentation for astronomy and particle physics experiment, where a thermal stage at approximately 1 K would allow an alternative heat sink to the still for electronics and radiation shielding, or quantum computer research where a large number of coaxial cables must be heat sunk in the cryostat. Furthermore, the behaviour of such a refrigerator is simplified due to the separation of the condenser stage from the dilution circuit, removing the complex interaction between the 4-K, Joule–Thomson, still and mixing chamber stages found in current dry DR designs.