Abstract: Disclosed are two-stage inter-phasing pulse tube refrigerators with and without shared buffer volumes.

Abstract: In an oil-lubricated helium compressor unit, the adsorber can retain all of the oil that might be transferred from the compressor to the adsorber before the system shuts down. No oil is ever transferred or transferable to, for example, the expander in a GM type refrigeration system connected to the unit. The compressor itself will shut down because of a protective switch or seize for lack of oil before any oil carries outside the compressor unit. The unit and the connected refrigeration system can run for more than a selected design life before the compressor shuts down because the limit of oil in the adsorber has been reached. The adsorber can retain as much oil as might leave the compressor over the life of the system plus a safety margin of at least 25%. The adsorber need not be serviced or replaced for the life of the system.

Abstract: In an oil-lubricated helium compressor unit, the adsorber can retain all of the oil that might be transferred from the compressor to the adsorber before the system shuts down. No oil is ever transferred or transferable to, for example, the expander in a GM type refrigeration system connected to the unit. The compressor itself will shut down because of a protective switch or seize for lack of oil before any oil carries outside the compressor unit. The unit and the connected refrigeration system can run for more than a selected design life before the compressor shuts down because the limit of oil in the adsorber has been reached. The adsorber can retain as much oil as might leave the compressor over the life of the system plus a safety margin of at least 25%. The adsorber need not be serviced or replaced for the life of the system.

Abstract: In an oil-lubricated helium compressor unit, the adsorber can retain all of the oil that might be transferred from the compressor to the adsorber before the system shuts down. No oil is ever transferred or transferable to, for example, the expander in a GM type refrigeration system connected to the unit. The compressor itself will shut down because of a protective switch or seize for lack of oil before any oil carries outside the compressor unit. The unit and the connected refrigeration system can run for more than a selected design life before the compressor shuts down because the limit of oil in the adsorber has been reached. The adsorber can retain as much oil as might leave the compressor over the life of the system plus a safety margin of at least 25%. The adsorber need not be serviced or replaced for the life of the system.

Abstract: Several layers of fine mesh screen are diffusion bonded together to form a rigid disc or plate that is self supporting and is a flow smoother at the ends of a pulse tube expander. Layers range from fine screens on the surface facing the pulse tube to coarser screens that provide structural support without significantly adding to pressure drop across the screen assembly. The flow smoother is typically used in series with a heat exchanger at the warm end that rejects heat to ambient from the gas of the pulse tube and a heat exchanger at the cold end that receives heat from the load being cooled.

Abstract: A GM type displacer has an elastomer “O” ring at the warm end to absorb impact energy when the displacer reaches the bottom of the stroke before it would hit the cylinder end cap. When the displacer reaches the top of its stroke, before the displacer would hit the internal mechanism of the expander, another elastomer “O” ring absorbs the kinetic energy of the displacer. Both absorbers are at or near ambient temperature.

Abstract: Mixed refrigerants provide refrigeration at cryogenic temperatures with throttling cycles operating with a one-stage compressor. The refrigerants include noncondensable gases such as helium, neon, or hydrogen to increase the overall cooling capacity of a refrigeration system at the same refrigeration temperature which is attainable without such noncondensable gases. More refrigeration can be produced with existing systems at temperatures above the normal boiling point of nitrogen or argon by adding, for example, helium, than for refrigerant blends without helium. By increasing the return pressure value of the refrigeration cycle in relation to the molar percent of helium present in the refrigerant, a constant refrigeration temperature may be maintained which exhibits greater stability than prior systems operating at the same temperature without helium enrichment.

Abstract: A Group I gas cryopumping system includes a compressor throttle cycle refrigerator using mixed refrigerants. Cold refrigerant flows through a cryopumping surface located in a vacuum chamber, whereon vapor freezes. The refrigerant then passes through a heat exchanger in cross flow with refrigerant from the compressor. Refrigerant flow entering and leaving the heat exchanger is in uninsulated lines at substantially room temperature. All exposed cold lines are eliminated. The throttle device and cold cryopumping surface are an integral unit that connects directly to the flow paths of the heat exchanger without intermediate lines. The compressor/aftercooler unit may be located at any convenient distance from the heat exchanger and cryopumping surface, and the heat exchanger is located immediately adjacent to the pumping surface in a separate housing outside the vacuum chamber. The heat exchanger housing may share or be isolated from the vacuum of the vacuum chamber.

Abstract: A cryogenic cold head in a canister is partially surrounded by an isolation mass. An open portion of the mass permits access for connection of a vapor compression refrigeration unit to the cold head, which is highly conductive. Straps of braided copper suspend the isolation mass from the cold head. The isolation mass and straps have a fundamental frequency that is below the first harmonic frequency at the cold head as caused by the refrigeration unit. A temperature differential between the cold head and a device-mounting interface on the isolation mass is preferably less than 2.5K per watt of heat transferred. The device to be cooled is mounted directly to the isolation mass when the mass of the device is insignificant relative to the isolation mass. For further vibration isolation, the device is separated from the isolation mass by another braided strap.

Abstract: 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.

Abstract: 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.

Abstract: A closed cycle cryogenic refrigerating system with a fixed restrictor operates with a compressor inlet pressure in a range of 0.1 Mpa to 0.4 Mpa and compressor discharge pressure in a range of 1.5 Mpa and 2.5 Mpa. A basic cryogenic refrigerant mixture is used to which is added approximately 3% to 25% of helium, hydrogen and/or neon. A ratio of refrigerant density at the inlet of the fixed restrictor between steady-state operation and operation at the beginning of cool-down is in an approximate range of 7 to 17. Relatively rapid cool-down is achieved and evaporator temperature is maintained in an approximate range of 70K to 120K.

Abstract: Apparatus and methods for cooling a superconducting magnet by circulating a pressurized helium gas through a convective cooling loop by natural convection, and apparatus and methods have been provided for quickly and effectively cooling a warm superconducting magnet down to operating temperature.

Abstract: In a cryostat, an isothermal boundary is proximate a large plurality of devices that are being cooled. The barrier is slightly colder than the devices so that heat flux therebetween is very small. The devices are in good thermal contact with a cold plate, which is made of a high thermal conductivity material. A single heater and a temperature sensor control the temperature of the cold plate as heat flows from the cold plate to the isothermal boundary. By limiting heat flow from the cold plate, temperature gradients throughout the temperature controlled region are very small. All of the devices to be cooled are very close to the same temperature. The isothermal boundary is maintained at the desired temperature by a flow of cryogenic refrigerant and a temperature sensor on the isothermal boundary provides inputs to a controller of refrigerant flow. The cryostat is constructed to minimize the amount of energy required from the heater to maintain the temperatures, and to minimize refrigerant flow.

Abstract: In the cryo-probe, refrigerant is furnished from a high pressure, room temperature supply. Insulation of the refrigerant lines is unnecessary. Refrigerant flows through a pre-cooling heat exchanger in the probe and through a restrictor wherein the pressure drops. In accordance with the Joule-Thompson effect, the refrigerant expands and becomes cold and liquid is applied in the region of the cryo-tip to provide rapid cooling thereof. Expanded refrigerant gas at low pressure reverses direction and flows back from the cold tip in counterflow arrangement through the aforementioned heat exchanger to give a pre-cooling effect to the refrigerant incoming from the external supply. A second tube for conveying warm-up gas is located in the probe and extends to the cold tip. After cryosurgery is complete, the high pressure flow is stopped and warm gas is delivered to the tip in the probe at reduced pressure through the second tube from the same refrigerant supply as is used for cooling.

Abstract: Apparatus and methods for low pressure cooling of superconducting magnets, for example, on a magnetic levitated train, through a separate circulation loop from a sealed, unvented thermal reservoir to provide a lightweight cooling system. In a second embodiment, forced flow cooling is directed to the superconducting magnets and shields through a separate circulation loop from a sealed thermal reservoir to further reduce the weight of the cooling system.

Abstract: A device for cryogenic refrigerating of an object below the triple point temperature of the cryogen. The device includes a housing in which is placed a porous plug. A liquid cryogen is supplied to one side of the plug at a pressure greater than the triple point of the cryogen. A pressure below the triple point is maintained on the other side of the porous plug. The cryogen flows through the plug and forms a solid on the supply side of the plug. The solid cryogen provides cooling by sublimation on a continuous basis to a cold station thermally coupled to the plug.

Abstract: A closed cycle refrigerating system for cryogenic temperatures using a single stage compressor with a refrigerant comprising a gas mixture. The refrigerating system includes a heat exchanger having a throttling orifice which is arranged to provide refrigeration, and a single stage oil lubricated compressor for compressing the refrigerant. The compressor is typically of the rolling piston type. The refrigerant is a mixture of at least one cryogenic gas having a normal boiling point below 120 degrees K and at least two other gases having normal boiling point temperatures below 300 degrees different from each other and from said one gas. There is also included means for cooling the compressed refrigerant and for circulating the cooled refrigerant to the heat exchanger and its throttling orifice and then back to the compressor. The system does not require any cascaded heat exchangers or intermediate phase separators.

Abstract: A cryostat in which a venting conduit is connected to a reservoir of the cryostat but no venting of cryogen within the reservoir can occur while fluid is flowing under pressure within the heat exchanger of the cryostat.

Abstract: A method and apparatus for cooling and filling a cryogen reservoir with liquid cryogen from the gas/liquid discharge of a heat exchanger. The cryogen reservoir has a cryogen liquid retaining material and a temperature sensing means remote from the heat exchanger. The gas/liquid discharge is located in a region within the reservoir proximate to the temperature sensing means. At least a portion of the discharge is passed through the liquid retaining material to be absorbed, thereby.