Advances in Cryogenic Engineering

Abstract

The Oxford Cryocooler incorporates a linear drive compressor operating close to resonance. All dynamic seals are non- contacting clearance seals maintained by mounting the piston and displacer on mechanical suspension systems with infinite fatigue life. The displacer is pneumatically driven but controlled by a miniature linear motor. The cooler is therefore non-wearing and performance can be maintained even in adverse environments by servo control of piston and displacer strokes and relative phase. The cooler was originally intended for spaceflight applications but has since been developed for military applications and there are lower cost versions for civil commercial applications. Many different coolers have been developed. Split and integral, single- and two-stage coolers have been produced with operating temperatures between 30 K and 200 K, refrigeration powers between 50 mW and several watts and capable of operating in ambient temperatures from -40°C to 70°C. A current project aims to extend the refrigeration power to 500 watts at 80 K. Experimental optimization techniques have been devised for rapid development of high efficiency coolers. Recently there has been considerable progress in the design, manufacture and assembly methods for linear motors, clearance seals and mechanical suspension systems.