A cryogenerator is a device that produces low temperatures at or near the temperature of liquid helium. Cryogenerators are often used to cool infrared sensors, superconducting devices, and other equipment that requires precise temperature control at cryogenic temperatures. There are a few main types of cryogenerators.
Stirling Cryocooler
One of the most common cryogenerator technologies is the Stirling cryogenerator. A Stirling cryogenerator uses the Stirling thermal cycle to transfer heat from a cold end to a warm end of the cryogenerator. This is done using a working gas that is transported between the cold and warm ends. During the compression phase of the Stirling cycle, the gas is compressed and the temperature increases, transferring heat to the warm end. The gas is then expanded, cooling the cold end below ambient temperature.
Stirling cryogenerators offer high reliability, durability, and multi-stage configurations to achieve very low temperatures. They are relatively inexpensive to manufacture and operate compared to other technologies. Some common applications of Stirling cryogenerators include cooling infrared detectors, superconducting magnets, and other electronic devices requiring cryogenic temperature control. Stirling cryogenerators can reliably cool to temperatures as low as 20 K.
Gifford-McMahon Cryogenerators
Another common type of Cryocooler is the Gifford-McMahon cryogenerator. Like Stirling cryogenerators, Gifford-McMahon cryogenerators use a gas working medium that undergoes compression and expansion phases. However, instead of using an oscillating mechanical mechanism, Gifford-McMahon cryogenerators utilize a reciprocating displacer and compressor to move the working gas between the cold end and warm end.
During operation, the cold working gas in the cold end is displaced into the warm region by the displacer. The gas is then compressed, raising its temperature and rejecting heat to the warm end heat exchanger. The compressed, warm gas is then expanded, absorbing heat from the cold end heat exchanger and cooling it to cryogenic temperatures. Gifford-McMahon cryogenerators can reach temperatures as low as 20 K and find applications in cooling infrared detectors, superconducting devices, and semiconductor devices.
Pulse Tube Cryogenerators
Another type of cryogenerator gaining popularity is the pulse tube cryogenerator. Pulse tube cryogenerators use the principles of pulse tube refrigeration to transport heat from the cold end to the warm end. In a pulse tube cryogenerator, a driver oscillates a gas at one end of a tube, creating a pressure wave that propagates to the other end.
The pressure wave does work on the gas, leading to compression and expansion phases. Placing appropriate heat exchangers and buffers at the cold and warm ends then allows heat to be pumped from the cold end to the warm end through the pressure wave cycling of the working gas. Pulse tube cryogenerators have no moving parts at the cold end, offering improved reliability. They can achieve temperatures as low as 10 K and have applications such as infrared detector cooling.
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