This invention relates to devices that provide low-temperature cooling, and, more particularly, to a solid state refrigerating device utilizing superconducting transitions to achieve cooling.
Many types of devices are operated at very low temperatures, such as, for example, 100K or less. In some cases, low temperature operation is required because physical or chemical processes of interest occur only at low temperature or are more pronounced at low temperature, and in other cases because some types of electrical-thermal noise are reduced at low temperature. An approach to cool the device to low temperature is therefore required as a basic part of such a system.
Cooling to low temperature becomes more difficult as the required temperature is reduced toward absolute zero. The simplest and most convenient approach to cooling a device to a low operating temperature is to immerse it in a liquid gas whose boiling point is at or above the desired operating temperature. This immersion ensures that the temperature of the device will not exceed the boiling point of the liquefied gas. Liquid nitrogen, having a normal boiling point of 77.4K, is readily available at a modest cost. Other liquid gases required to achieve lower temperatures, such as liquid neon and liquid helium having normal boiling points of 27.2K and 4.2K, respectively, are available but much more expensive.
While an immersion approach is preferred for laboratory and other stationary cooling requirements, the cooling of small devices in mobile apparatus, or other situations that make the use of liquid coolants difficult, requires another approach. For example, it may not be possible to provide liquefied gas to a device operated in a remote site, or in space. Also, it may be inconvenient or impossible to periodically service devices stored for long periods of time before use with liquefied gas.
Various approaches have been developed to keep apparatus cold without using liquefied gas as an immersion coolant. For example, gas expansion coolers expand compressed gas through an orifice, thereby cooling the gas and resulting in absorption of heat from a cooling load. Several types of thermoelectric devices can also be used for cooling. Such thermoelectric refrigerating devices are convenient, because only electrical power is required to achieve cooling and electrical power is available nearly everywhere. Thermoelectric devices are typically used in a stand alone cooler, heat sinked to ambient environment.
There is a continuing need for refrigerating devices that can cool to low temperature with a high cooling power. The present invention fulfills this need, and further provides related advantages.