Dry dilution refrigerator with 4He-1 K-loop

In this article we summarize experimental work on cryogen-free He-3/He-4 dilution refrigerators which, in addition to the dilution refrigeration circuit, are equipped with a He-4-1 K-stage. This type of DR becomes worth considering when high cooling capacities are needed at T similar to 1 K to cool cold amplifiers and heat sink cables. In our application, the motivation for the construction of this type of cryostat was to do experiments on superconducting quantum circuits for quantum information technology and quantum simulations. In other work, DRs with 1 K-stage were proposed for astro-physical cryostats. For neutron scattering research, a top-loading cryogen-free DR with 1 K-stage was built which was equipped with a standard commercial dilution refrigeration insert. Cooling powers of up to 100 mW have been reached with our 1 K-stage, but higher refrigeration powers were achieved with more powerful pulse tube cryocoolers and higher He-4 circulation rates in the 1 K-loop. Several different versions of a 1 K-loop have been tested in combination with a dilution refrigeration circuit. The lowest temperature of our DR was 4.3 mK. (C) 2014 Elsevier Ltd. All rights reserved.