Development of a Light Weight Linear Drive Cryocooler for Cryogenically Cooled Solid State Laser Systems

Abstract

This paper describes the development and testing of a free piston, linear drive cryocooler designed to meet specific requirements for a light weight, airborne, cryogenically cooled semiconductor laser system. The function of the laser and how the cryocooler is used in the laser will be described.

The basic cryocooler is an in-line configuration which was initially developed to support high temperature super conductor (HTS) device cooling. Because of its relatively high capacity (8 Watts at 65 K) and high degree of modularity, this unit was selected as the baseline for the significant weight reduction process which was required to meet laser system weight constraints. The cryocooler employs a moving iron linear drive motor and flexurally supported moving components to eliminate wear as potential cause for performance degradation.

The weight reduction process started with a 60 pound cooler and reduced the weight to 30 pounds without changing its performance significantly. A second phase of this program is currently ongoing to reduce the weight to 20 pounds. Finite element analysis was used to optimize the weight and strength.

A description of the cryocooler operating requirements along with mechanical details of the gas compressor, cold head, heat rejection system, and supporting electronics is provided. Issues concerning the hardware changes required in the weight reduction program and their impact on cooler operating characteristics are discussed. A comparison between the performance of the In-Line cooler and the light weight version is presented.