Advanced Compressor for Long-Life Cryocoolers

Abstract

This paper describes work performed to demonstrate the potential advantages (high reliability, low weight, long life) of a hermetically sealed diaphragm-type compressor that separates the gas cycle from the drive system and uses a moving-magnetic-type motor. To accomplish this objective, a “proof of concept” compressor was designed, built, and tested. The original intent was to use the compressor to drive a 30 K, 0.5-W orifice-pulse-tube cryocooler requiring 250 W of pressure-volume (PV) power. The compressor was developed to address these requirements and optimize the overall cryocooler performance by minimizing electrical input power and compressor weight. The proof-of-concept compressor differed from a flight-type design in that it used O-ring-type seals instead of welded hermetic closures and was made of bar stock construction. All other significant components were consistent with a space-flight hardware design. A pulse-tube simulator was used to load the compressor, allowing it to produce the desired pressure amplitude, phase angle, and PV power when operated at design stroke and frequency. With the compressor operating between 0.5 and 1.2% of design frequency, stroke, mean pressure, pressure amplitude, and phase angle, the PV power and estimated efficiency exceeded design values by approximately 4%, thus demonstrating the performance advantages of a diaphragm-type compressor.