Cryogenic refrigeration system with dual circuit heat exchanger

Claim 1

A cryostat refrigeration system comprising: a mandrel with temperature sensing means disposed therein, said temperature sensing means having electrical conduit means extending outwardly of said mandrel for connection to a temperature indicating means; a dual circuit heat exchanger disposed around said mandrel; said heat exchanger comprising a first tube with a first end to be connected to a source of high pressure gas and a second end containing a Joule-Thompson orifice having a plurality of fins disposed thereon generally perpendicular to the axis of the first tube, a second tube smaller in diameter than said first tube and disposed within said first tube, said second tube having an inlet end connected to a source of high pressure gas and an exit end projecting beyond the end of said first tube containing the expansion orifice said projection being of a length to create a pressure drop of the high pressure gas in the projecting end of said second tube thereby achieving refrigeration; means for introducing high pressure gas into each of said tubes; whereby when operating said second tube promotes rapid cooldown of the system under an initial high rate of gas flow and after low temperature is indicated by the thermocouple the level of refrigeration can be maintained by throttling back the flow in the second tube substantially while maintaining a lesser flow in the first tube.