A circulating loop for transporting refrigeration to a remote location is connected serially between a Gifford-McMahon (GM) or GM type Pulse Tube cold head and the compressor. Either high pressure gas from the compressor can flow through the remote heat station before returning to the cold head or low pressure gas can flow from the cold head to the remote heat station before returning to the compressor. A first fraction of gas, which may include all of the gas at ambient temperature, enters a counter-flow heat exchanger, is cooled by the cold head, flows to the remote load, and then returns to ambient temperature as it flows through the counter-flow heat exchanger. The high or low pressure line may have a circulation control valve that diverts a second fraction of gas to flow directly between the cold head and compressor. A controller adjusts the circulation control valve to optimize the cooling of the load.

A circulating loop for transporting refrigeration to a remote location is connected serially between a Gifford-McMahon (GM) or GM type Pulse Tube cold head and the compressor. Either high pressure gas from the compressor can flow through the remote heat station before returning to the cold head or low pressure gas can flow from the cold head to the remote heat station before returning to the compressor. A first fraction of gas, which may include all of the gas at ambient temperature, enters a counter-flow heat exchanger, is cooled by the cold head, flows to the remote load, and then returns to ambient temperature as it flows through the counter-flow heat exchanger. The high or low pressure line may have a circulation control valve that diverts a second fraction of gas to flow directly between the cold head and compressor. A controller adjusts the circulation control valve to optimize the cooling of the load.

A cryogenic cooling system is provided comprising: a cooled plate (2) thermally coupled to a cryogenic refrigerator (9), a heat switch assembly and a target assembly (5). The target assembly (5) comprises a target refrigerator (12) configured to obtain a lower base temperature than the cryogenic refrigerator (9). The heat switch assembly (18) comprises one or more gas gap heat switches, the heat switch assembly (18) having a first end thermally coupled to the cooled plate (2) and a second end thermally coupled to the target assembly (5). A sorption pump (22) is provided for controlling the thermal conductivity across the heat switch assembly (18) in accordance with the temperature of the sorption pump (22) The sorption pump (22) is thermally coupled to the cryogenic refrigerator (9), by a thermal link (46) extending from the cooled plate (2) to the heat switch assembly (18). The sorption pump (22) is arranged at a position along the thermal link (46) between the heat switch assembly 18 and the cooled plate (2).

A cryogenic cooling system is provided comprising: a cooled plate (2) thermally coupled to a cryogenic refrigerator (9), a heat switch assembly and a target assembly (5). The target assembly (5) comprises a target refrigerator (12) configured to obtain a lower base temperature than the cryogenic refrigerator (9). The heat switch assembly (18) comprises one or more gas gap heat switches, the heat switch assembly (18) having a first end thermally coupled to the cooled plate (2) and a second end thermally coupled to the target assembly (5). A sorption pump (22) is provided for controlling the thermal conductivity across the heat switch assembly (18) in accordance with the temperature of the sorption pump (22) The sorption pump (22) is thermally coupled to the cryogenic refrigerator (9), by a thermal link (46) extending from the cooled plate (2) to the heat switch assembly (18). The sorption pump (22) is arranged at a position along the thermal link (46) between the heat switch assembly 18 and the cooled plate (2).

A cryogenic cooling system is provided comprising a primary insert (118) and a demountable secondary insert (128). The primary insert (118) comprises a plurality of primary plates (111, 112), each primary plate having a primary contact surface, and one or more primary connecting members (117) arranged so as to connect the plurality of primary plates (111, 112). The demountable secondary insert (128) comprises a plurality of secondary plates (121, 122), each secondary plate having a secondary contact surface, and one or more secondary connecting members (127) arranged so as to connect the plurality of secondary plates (121, 122) such that the secondary insert (128) is self-supporting. One or more adjustment members are configured such that, when the secondary insert (128) is mounted to the primary insert (118), the adjustment members cause the primary and secondary contact surfaces of the respective primary (111, 112) and secondary plates (121, 122) to be brought into conductive thermal contact.

A cryogenic cooling system is provided comprising a primary insert (118) and a demountable secondary insert (128). The primary insert (118) comprises a plurality of primary plates (111, 112), each primary plate having a primary contact surface, and one or more primary connecting members (117) arranged so as to connect the plurality of primary plates (111, 112). The demountable secondary insert (128) comprises a plurality of secondary plates (121, 122), each secondary plate having a secondary contact surface, and one or more secondary connecting members (127) arranged so as to connect the plurality of secondary plates (121, 122) such that the secondary insert (128) is self-supporting. One or more adjustment members are configured such that, when the secondary insert (128) is mounted to the primary insert (118), the adjustment members cause the primary and secondary contact surfaces of the respective primary (111, 112) and secondary plates (121, 122) to be brought into conductive thermal contact.

In a gamma free-piston Stirling cooler driven by linear electric motors, a motor operating frequency for consuming minimum electric power is detected and a different motor operating frequency that delivers maximum thermal cooling power is detected. The frequencies are detected by varying the operating frequency in small steps while sensing (1) the motor power input to maintain a steady temperature or (2) the thermal cooling power of the Stirling cooler. A mode detection routine detects whether the appropriate freezer operation is the electric power minimization mode or the thermal cooling power maximization mode based upon the current thermal conditions in the freezer. When the freezer is sufficiently cold, the pistons of the Stirling cooler are driven at the minimum electric power consumption frequency. When the temperature is, or is likely to become, too warm, the pistons of the Stirling cooler are driven at the maximum thermal cooling power frequency.

In a gamma free-piston Stirling cooler driven by linear electric motors, a motor operating frequency for consuming minimum electric power is detected and a different motor operating frequency that delivers maximum thermal cooling power is detected. The frequencies are detected by varying the operating frequency in small steps while sensing (1) the motor power input to maintain a steady temperature or (2) the thermal cooling power of the Stirling cooler. A mode detection routine detects whether the appropriate freezer operation is the electric power minimization mode or the thermal cooling power maximization mode based upon the current thermal conditions in the freezer. When the freezer is sufficiently cold, the pistons of the Stirling cooler are driven at the minimum electric power consumption frequency. When the temperature is, or is likely to become, too warm, the pistons of the Stirling cooler are driven at the maximum thermal cooling power frequency.

The object of this invention is to increase the life of the displacer and stem seals of the reciprocating displacer of a Gifford McMahon (GM) cryogenic expander. The seal comprises a ring that is relatively long and thin and uses the pressure difference across the seal, acting behind the ring, as the primary force to bring the ring into contact with the cylinder and stem walls. The pressure difference across the seal ring pushes the ring to one end of the groove, and the friction force pushes the ring in the same direction while it is moving. The sealing force is distributed over a larger area compared with a conventional backed “O” ring thus reducing the wear rate and increasing the seal life.

The object of this invention is to increase the life of the displacer and stem seals of the reciprocating displacer of a Gifford McMahon (GM) cryogenic expander. The seal comprises a ring that is relatively long and thin and uses the pressure difference across the seal, acting behind the ring, as the primary force to bring the ring into contact with the cylinder and stem walls. The pressure difference across the seal ring pushes the ring to one end of the groove, and the friction force pushes the ring in the same direction while it is moving. The sealing force is distributed over a larger area compared with a conventional backed “O” ring thus reducing the wear rate and increasing the seal life.