Variable flow cryostat with dual orifice

Claim 1

A cryostat of the type wherein a working fluid is expanded through an orifice associated with the cold end of a heat exchanger used to cool the working fluid before expansion through the orifice to produce an inventory of liquefied working fluid adjacent the orifice, the improvement comprising: first means contained within said cryostat to initiate fluid flow through said orifice at a high rate to provide initial rapid cool-down of said cryostat; said first means interrupting fluid flow after cool-down and remaining inoperative until working fluid source pressure decays to a value approximately one-half the initial value at room temperature and above; second means associated with said heat exchanger to permit continuous flow of working fluid through said heat exchanger and continuous production of liquefied working fluid; whereby said cryostat operates with continuous minimum fluid flow to maintain maximum heat transfer between said liquefied working fluid and an object being cooled by said cryostat.