A Multi-Stage Hybrid 10 Kelvin Cooler

Future Department of Defense space-based systems will require long-life, active cryocoolers capable of achieving sub-10 K load temperatures. Currently, the available cryocooler technology at these temperatures is too massive and inefficient. In many cases, reliability is low and vibration high. During the proposed, Phase II project we will fabricate and test an innovative cooling system that directly interfaces a recuperative, reverse-Brayton low temperature stage with a regenerative, pulse-tube upper stage. This hybrid, multi-stage cryocooler has the potential to be an efficient and compact device capable of meeting the cryogenic cooling needs of the Air Force. The system offers additional benefits related to easy thermal, electrical, and mechanical integration, high reliability, and low vibration. During the Phase I project, we developed a detailed thermodynamic model of the proposed cryocooler and validated some aspects of that model against experimental data. Another result of the Phase I project was the development and demonstration of an efficient and practical rectifying interface, required to convert the oscillatory pulse-tube flow into a continuous flow appropriate for the recuperative stage. The key component in the interface, the check-valves, demonstrated flow and dynamic characteristics appropriate for the hybrid cooler. The implementation of the interface system did not have a substantially negative effect on the performance of the pulse-tube stage. This interface represented a key technical challenge for the hybrid cryocooler.