Bimaterial demand flow cryostat

Claim 1

In a demand flow cryostat wherein (1) a refrigerant is supplied through an elongated heat exchanger having a warm end and a cold end disposed in a container, (2) the refrigerant is expanded through a Joule-Thompson expansion orifice at the cold end of the heat exchanger to produce an inventory of liquid in the container proximate the cold tip of the cryostat, and (3) a valve member for controlling refrigerant flow through the orifice is disposed adjacent to the orifice and is movable relative to the orifice to effect a throttling movement between the orifice and the valve member with reduction in temperature, whereby flow of refrigerant through the orifice is controlled as a function of the temperature, the improvement which comprises separate mounting means for the orifice and for the valve member disposed and affixed relative to each other so as to provide relative movement therebetween, each of the mounting means operably cooperating with its respective control element and being movable in response to the expansion and contraction of the control elements, and the control elements being composed of different materials whose mean cryogenic linear coefficients of expansion differ by at least about 1×10 -5 /° K.