Precision Temperature Control of Stirling-Cycle Cryocoolers

Abstract

Linear-drive Stirling-cycle cryocoolers designed with non contacting parts are ideal for long-life cryogenic cooling applications. These cryocoolers are light weight, have an almost unbounded operational life, and require no expensive ground handling equipment or procedures. One of the challenges in applying these refrigerators to sensitive instruments is precision temperature control. Developing a closed loop temperature control system for a Stirling-cycle cryocooler has been a recent project at the Lockheed Research & Development Division.

This paper describes the analysis, development, and laboratory testing of a closed loop control system that maintains temperature over a range of 50 to 80 K to ±0.01 K. The control loop uses position, velocity, and integrated error information to achieve excellent short-term and long-term temperature stability by modulating the length of the compressor stroke. The resulting control system is compatible with adaptive vibration cancellation techniques. The control algorithm is implemented on a personal computer using a 386 processor, but it is simple enough to run as one of many tasks on a less powerful microprocessor.