Modeling, development, and experimental validation of a Joule–Thompson superfluid refrigerator using a pulse tube cryocooler

• We present a comprehensive model, design, and construction of our 1 K refrigeration system.
• Our system is economically viable: using existing pulse tube cryocoolers to liquefy and subcool He from room temperature.
• Our system attained a base temperature of 1.39 K and it provides a cooling power of 150 mW at 1.65 K.
• Various parameters in the design model can be adjusted for optimal performance.

An economical method of refrigeration to temperatures near 1 K is introduced in this work. Unlike traditional methods, our refrigeration system does not rely on the use of a helium bath; helium enters a Dewar at room temperature and pre-cools, condenses, and sub-cools to temperatures slightly lower than the normal boiling point of helium during its heat exchange with various components that are connected to a Cryomech pulse tube cryocooler (PT-410). A fixed Joule–Thompson restriction valve is used to create a large pressure difference between the incoming high-pressure helium line and the vacuum pumped space of the 1 K pot causing the helium temperature to drop to its corresponding saturation condition in the pot upon an isenthalpic expansion across the valve. This is a comprehensive report on the performance of a Joule–Thompson superfluid refrigerator; we will discuss our model, techniques in the experimental setup, and present our data for this type refrigerator. This refrigerator reached an ultimate low temperature of 1.39 K with no applied heat load and provided 150 mW of cooling power at 1.65 K.