A cold station thermal switch at the end of a cold finger in cooperation h the detector on an inner dewar wherein the thermal switch opens at the cool down cryogenic temperature to prevent vibrations from the cooler system from being transmitted to the detector. The thermal switch has an outer bellows fitted around the end of the last stage of the cooler which extends close to but not in contact with the detector and an inner bellows having a metallic bumper on the end thereof in contact with the detector until cool down to the operating cryogenic temperature at which time contraction of the inner bellows disconnects the metallic bumper from the detector.

A chemisorption refrigeration system includes dual containers containing a material such as silver which is alternately heated and cooled to chemically desorb and reabsorb oxygen gas. The gas is desorbed at high temperature and pressure and is pre-cooled and then passed through a Joule-Thomson valve where it is expanded and partially liquefied to provide cooling at 60.degree.-100.degree. K. The liquefied oxygen is then boiled and returned to a cooled container where it is reabsorbed. By alternately heating and cooling the containers, a continuous source of high pressure high temperature oxygen can be provided.

The electrical connector in accordance with the present invention may be used for signal transmission/reception between a card and a circuit of a machine concerned, for example. The electrical connector has a frame to which attached are a rear structure having a card inserting/pulling port and a connector body having a contact group. Also attached to the frame are a longitudinally movable slider and a shaft having a swing fulcrum. The slider has engagement pawls adapted to be engaged with a card, and the shaft has an operating knob having a card holding portion. When the slider advances with the insertion of a card, the shaft is swung so that the operating knob is pushed out and the holding portion comes in contact with the rear end surface of the card, thereby to prevent the card from being erroneously pulled out.

A dual refrigeration system for cooling a sink device is described, which automatically thermally couples the cold refrigerator to the sink device while thermally isolating the warm refrigerator from the sink device. The system includes two gas gap heat switches that each thermally couples one of the refrigerators to the sink device, and a pair of sorption pumps that are coupled through tubes to the heat switches. When the first refrigerator (18) is operated and therfore cold, the first pump (50) which is thermally coupled thereto is also cooled and adsorbs gas to withdraw it from the second heat switch (44), to thereby thermally isolate the sink device (12) from the warm second refrigerator (26). With the second refrigerator being warm, the second pump (52) is also warm and desorbs gas, so the gas lies in the first switch (38), to close that switch and therefore thermally couple the cold first refrigerator (18) to the sink device. Thus, the heat switches are automatically switched according to the temperature of the corresponding refrigerator.

A refrigerator having a pressurizing device, a coldness generating device for generating coldness by expanding a portion of operating fluid which has been pressurized by the pressurizing device and a fluid passage through which the operating fluid is, via a device to be cooled, again circulated to the pressurizing device after the residual portion of the operating fluid has been cooled by the coldness generating device. A regenerator type heat exchanger is disposed in the fluid passage through which the operating fluid passes, and a switch device switches the flow of the operating fluid in the fluid passage to the reverse direction at a predetermined time period.