A Three-Stage Stirling Pulse Tube Cryocooler Approaching 4 K

Abstract

It is a great challenge for a Stirling Pulse tube cryocooler (PTC) to reach liquid-helium temperature, where there are promising applications such as superconducting digital electronics, midinfrared instrument, heterodyne detectors. Lockheed Martin first achieved a temperature below 4 K with a four-stage configuration with He-3 as working fluid. A single-stage Stirling PTC precooled by a self-made two-stage GM-type PTC has been constructed and tested to explore the loss mechanism of 4 K PTC working at high frequency at Zhejiang University. Temperature as low as 4.2 K has been successfully obtained with He-4 as working fluid by the end of 2008. In this paper, we report a newly-designed three-stage PTC, which aims to reach 4 K. The 4 K cooler is a thermalcoupled type, whose mass flows are easier t ocontrol and whose energy flows are more readily monitored. It will be working with He-4 instead of He-3. The first and second stages have been finished. A bottom temperature of 35 K and 9 W at 77 K with 300 We input has been achieved in the first stage. The bottom temperature of second stage is as low as 20.6 K, and the cooling power is measured as 1.0 W at 28.6 K. The test results are in good agreement with the model for both stages. The first and second stage is designed to couple with the a stage, which is expected to reach below 5.0 K at 30 Hz.