Design and Test of a 70 K Pulse Tube Cryocooler

Abstract

Fuji Electric has designed, fabricated and tested a 70 K pulse tube cryocooler. The cryocooler was designed for commercial use to provide 2 to 3 W at 70 K. The basic concept of this cryocooler is compactness, low cost, high reliability and high performance. A compressor is a key part for providing a compact cryocooler. The compressor is composed of dual-opposed-pistons that move with a coil. A new concept for supporting the moving units with flexure bearings enables a smaller size in the axial direction. The reduction or integration of parts significantly diminishes the cost of the compressor. The pulse tube part of the cryocooler is implemented in an in-line configuration in order to provide high cooling performance. Dimensions of the pulse tube, regenerator geometry and phase shifter are optimized by experimental methods. In addition, the cooling performance has been enhanced by optimization of the compressor. Application of these technologies enables the pulse tube cryocooler to provide a cooling capacity of 2.5 W at 70 K with 100 W electrical input. Reliability is one of the most important requirements, and component reliability tests, which include mechanical fatigue of the flexure bearings and contamination of the helium working gas, were conducted. The lifetime of the cryocooler is expected to be more than 50,000 hours.