Effects of working fluid on performance of 4.5 K JT cooler

Abstract

NASA is considering a “probe” class mission with a far-infrared imaging and spectroscopy space telescope. A critical technology need for this mission is an efficient, high capacity, low-temperature cryocooler with low exported vibrations to enable its cryogenic instruments to achieve exquisite sensitivity and low internal noise to observe far distant faint cosmic sources. This paper discusses the design of a 4.5 K hybrid cooler consisting of a pulse tube precooler and a JT stage. The JT stage uses 3He as its working fluid to achieve a low cooling temperature of 4.5 K. The cooler will build on the JWST MIRI spare flight cooler, using existing TRL 9 component and subsystem hardware technologies. The paper will discuss the cooler configuration, thermodynamic design, predicted performance, and sensitivity to operating conditions. The impact of pressure drops and thermal ineffectiveness in the JT stage recuperators are discussed and compared to those in the MIRI cooler. Finally, test results for MIRI Development Model (DM) compressor with 4He are presented. Test data include compressor volumetric flow rates and power inputs at different pressure ratios and piston stroke lengths. The DM compressor test results and flight compressor test data collected during MIRI spare flight cooler acceptance testing both indicate that the 4.5 K cooler will be able to meet the cooling requirement of 48 mW at 4.5 K and 230 mW at 18 K with a significant margin.