Performance Investigations of a 4 to 10 K Long‐Life Mechanical Cryocooler

We believe that the quickest way of obtaining a reliable space cooler in the range of 4 to 10 K is to combine a Stirling mechanical cooler with a Joule‐Thomson (J‐T) cooler. In this approach we perform the bulk of the cooling with the Stirling cooler and use the J‐T cooler for the small amount of cooling required at the lowest temperatures. The recuperative J‐T stage can reach low temperatures more easily because it does not have the regenerator limitations shared by Stirling and Pulse Tube mechanical coolers. We present our system concept in detail and discuss its merits.To demonstrate the capabilities of a hybrid cooler, we built a breadboard version consisting of a precooler, a J‐T circulating compressor, and a cold head. With it we achieved closed‐cycle refrigeration rates of 35 mW at 6 K and 10 mW at 3.7 K. For simplicity we used a commercial Gifford McMahon (GM) refrigerator as our precooler and focused on building the J‐T compressor and passive cold head. The J‐T compressor was an Oxford‐style line...