The GTLT cryocooler, a low temperature variant of CryoTel® GT

Abstract

The CryoTel® GT is an integral Stirling cryocooler with 16 W of lift capacity at 77 K with a nominal input power of 240 W. The GT has been a Sunpower legacy product since it was brought to commercialization in 2005. The contact-free operation of the moving components by using Sunpower’s gas bearings technology results in a long lifetime of the cooler, achieving an MTTF of over 200,000 hrs. Typical no-load temperature of GT is around 36 K. Sunpower used an advanced regenerator to improve the performance and was able to provide cooling lift below 35 K. Although the advanced regenerator effectively improved the cooler performance, overall cryocooler cost went up substantially due to the costly special processes and materials for the regenerator. Looking for a cost-effective alternative, Sunpower applied optimization techniques and developed a regenerator design improving its performance at lower temperature. To reduce the conduction loss of the cold finger, an alternative material for stainless steel was selected. Its material cost is a little higher than stainless and the thermal conductivity is between titanium and stainless. It is weldable into the transition using the same methods and geometry as the current stainless cold finger which is a huge benefit. Sunpower built 6 units and achieved an average no-load temperature of 26.5 K, about 9 K colder no-load temperature than standard GT, at the same input power. This low temperature variant of GT is named as GTLT and we are moving to add the GTLT as a commercial product.