Compact 10K Hybrid Cryocooler

Long life mechanical cryocoolers for space applications have matured during the last decade, and 77 K and 35 K coolers are now available. However, 10 K equivalents are not available because fundamental regenerator performance limitations are being reached making them relatively power inefficient. There are technical ways around these regenerator limitations. For example, Joule Thomson (JT) coolers do not suffer this particular limitation because they use uni-directional DC flow and counterflow heat exchangers. However, they require substantial precooling and a practical cooler for a 10 K application requires both a JT cooling system with a Stirling/Pulse tube precooler. At present, these are the most practical way of reaching 10 K. Current realizations of hybrid coolers are the bulky combination of two separate coolers, the precooler and the JT cooling loop The JT and Stirling compressors are similar except the JT compressor uses valves to rectify the AC pressure wave and produce the DC flow for the expansion. Our approach is to drive the remote JT cold head using a valve set at the Stirling precooler cold tip, essentially creating a cold compressor. This will result in the elimination of a large amount of hardware including the JT compressor.