Apd Cryogenics, Inc.

Intermagnetics General Corporation

Michael Boiarski

Ralph C Longsworth

Boris V Yudin

Ajay N Khatri

Dennis H Hill

F Scott Murray

Leo Blecher

Philip A Jonas

Anthony L Owoc

Lawrence A Klusmier

An integral combination of expansion valve and evaporator in a cryostat using a single support member. The valve includes two flow orifices, one orifice being used primarily for steady-state operation and the other orifice being used only during cool-down. An actuator having a high coefficient of thermal expansion moves a needle positioned in the cool-down orifice such that a large orifice flow area at the start of cool-down is automatically and continuously reduced as the actuator temperature decreases as refrigerant is throttled through the orifice. Within a range of approximately 30 K from the desired steady-state evaporator temperature, the needle completely blocks the cool-down orifice. Then, refrigerant flows through the steady-state orifice which has a remotely adjustable needle. In the final stage of cool-down, the refrigerant system is entirely controlled by the steady-state orifice and its associated needle. In other embodiments, the steady-state orifice and adjusting needle, are replaced with a fixed restrictor, such as a capillary tube, that is positioned in parallel with the cool-down orifice and needle. The fixed restrictor is sized to satisfy the desired steady-state operating conditions.

Closed cycle cryogenic refrigeration system with automatic variable flow

A MRI cryostat, which contains a superconducting magnet operating in a bath of liquid helium, reduces the boil-off rate of helium by intercepting most of the heat in-leakage by means of a throttle cycle (TC) refrigerator operating at a low side temperature of about 90K. The main heat exchanger for the throttle cycle refrigerator is located within or immediately adjacent to the cryostat housing and delivers cold liquid to a cold heat exchanger that is in thermal contact with an outer radiation shield, support struts, neck tube and electrical leads inside the cryostat. Heat is intercepted by the outer shield from essentially all paths between a 300K ambient and a 4K load temperature, which temperature results from liquid helium boil-off to atmosphere. A second, inner radiation shield at 35K is cooled by gaseous helium that boils from the liquid helium bath. There are no moving parts of the refrigeration system in the cryostat. Thus, vibration, noise and disturbance of the magnetic field are reduced. The refrigerator installation is small and low in cost; power consumption is reduced relative to the prior art.

MRI cryostat cooled by open and closed cycle refrigeration systems

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Moscow, Russia

Michael Boiarski