Precooling system for a Joule - Thomson cryogenerator: design and experimental results

In order to construct a cryogenerator that applies the Joule-Thomson expansion process to obtain 0.5 W at 4.2 K, a prerefrigerating system for the helium gas entering the Joule-Thomson valve is needed. This system can be realized by means of a two-stage Gifford-McMahon cryogenerator. The paper indicates some preliminary measurements carried out with the prototype of the prerefrigerating device, as well as some measurements of thermal regenerator effectiveness carried out with a similar, though smaller-sized, device. It outlines the projects of the counterflow and isothermal heat exchangers of the precooling system, and describes the thermal switch connecting the Joule-Thomson stage to the Gifford-McMahon cryogenerator.