Performance of a Two-Stage Pulse Tube Cryocooler for Space Applications

Abstract

Lockheed Martin has developed a two-stage pulse tube cryocooler under contract to the Air Force Phillips Laboratory. The cooler is an intermediate bypass design in an in-line configuration. At a reject temperature of 295 K, the cooler simultaneously produced 0.6 W at 56 K and 0.32 W at 35 K. With no heat load on either stage, the cold stage reached 23 K and the intermediate stage reached 48 K. This cooler was driven by a 10.9 cm³ swept volume flexure bearing compressor, developed by Lockheed Martin for low-cost cryocooler applications. We also observed evidence of dc mass flow through the intermediate capillary and speculate that this resulted in some loss in second-stage cooling power. We observed unstable behavior of the second-stage temperature which we also attribute to dc flow.

We evaluated an etched foil regenerator. While analysis suggested significant improvement with this technology, tests in both pulse tubes and Stirling-cycle coolers showed poorer performance compared to the conventional screen regenerators.

As part of this contract we also evaluated linear flexures for reduction of lateral exported compressor vibration. In a direct comparison with spiral flexures in the same compressor, the linear flexures reduced the lateral vibrations by a factor of three to four for the higher harmonics.