Compact 2.2 K Cooling System for Superconducting Nanowire Single Photon Detectors

We are developing a compact, low-power, closed cycle cooling system for superconducting nanowire single photon detectors. The base temperature of the present prototype, which uses a helium-4 Joule-Thomson stage, is 2.2 K with over 1.2 mW of cooling. This stage is precooled to 10 K using a three-stage linear compressor pulse tube cooler. A fully optimized system is projected to consume less than 250 W of wall power, and fit within a standard fan-cooled equipment rack enclosure. To-date, the pulse tube coldhead, pulse tube compressor, Joule-Thomson expansion stage, and Joule-Thomson counterflow heat exchangers have been developed, and performance tests show that design goals have been met. Substituting helium-3 for helium-4 should result in temperatures approaching 1 K. Future work includes development of the Joule-Thomson compressor, drive and control electronics, and further optimization of the pulse tube and Joule-Thomson coldheads.