Development of a Moving Magnet Linear Motor Pressure Wave Generator for a Pulse Tube Refrigerator

Abstract

A pressure wave generator (PWG) is the most critical component of a high frequency pulse tube cooler which is finding increased use in aerospace and ground applications, including the telecommunication sector. High efficiency, compactness, low weight, high reliability and low vibration are some of the most challenging attributes in its design. This paper describes the developmental studies of a moving magnet linear motor PWG of 2 cc swept volume with a dual opposed piston configuration. The generative and restoring force characteristics of the magnetic circuit have been evaluated using a force measurement set up. Spiral arm flexures have been designed using FEM, fabricated and qualified by test. The linear motors alone are tested under resonant conditions without gas spring forces to estimate the iron losses of the motors. The influences of coil wire cross-section and number of coil turns on the performance of the PWG have been studied experimentally. The paper describes the significant effect of compressor flow discharge line cross section on the efficiency of the system. The performances of the PWG at different gas fill pressures and operating frequencies have been investigated. With an input power of 35.2 W, the PWG has produced a shaft power of 26.8 W and an acoustic power of 18.7 W.