30 – 50 K Single Stage Pulse Tube Refrigerator for HTS Applications

Abstract

The need for reliable cryocoolers for High Temperature Superconducting (HTS) applications ranging from 30 to 50 K has become apparent in the past several years. Many cryocooler designs are under development, including GM, Stirling, and pulse tube. Pulse tube refrigerators have attracted extensive interest in recent years due to their high potential for reliability and simplicity. This paper describes the development program of a 30 – 50 K single stage pulse tube refrigerator for use in a HTS system at American Superconductor Co. Initial tests indicate that the cooler can reach a minimum temperature below 20 K and has a cooling capacity of 20 watts at 30 K, and 60 watts at 50 K, with an input power of 6 kW. Systematic investigation of the effects of valve timing, operating frequency and compressor input power on the cooler performance is presented in the paper. Additionally, the stability issue of the pulse tube refrigerator is addressed. The progress towards development of a successful 30 – 50 K pulse tube and its potential and limitations are also discussed.