Cryogenics

Cryogenics is the science and technology of producing and studying very low temperatures, including methods for liquefying gases and handling cryogenic materials.

Joule–Thomson effect: A gas changes temperature when it expands through a restriction without exchanging heat with its surroundings. This effect enables gas-expansion stages in many refrigeration and liquefaction cycles.
Absolute zero: The lowest possible thermodynamic temperature, defined as zero kelvins. Cryogenic temperatures approach this limit but cannot attain it through finite processes.
Magnetic resonance imaging: A medical imaging technique that uses nuclear magnetic resonance in strong magnetic fields. Many MRI magnets are superconducting and cooled with liquid helium or cryocoolers.
Refrigeration: The removal of heat from a space or substance to lower or maintain its temperature. Cryogenics extends refrigeration to temperatures where gas liquefaction and unusual material behavior matter.
Hydrogen embrittlement: Loss of ductility or fracture resistance in a material caused by hydrogen entering its structure. Cryogenic hydrogen systems must manage material damage as well as extreme cold and leakage.
Linde cycle: A gas-liquefaction process that cools compressed gas through heat exchange and Joule–Thomson expansion. It shows how regenerative cooling can turn compressed air into liquid.
Kelvin: The SI base unit of thermodynamic temperature, with its zero at absolute zero. Cryogenic temperatures are conventionally stated on the kelvin scale.
Superconducting magnet: An electromagnet whose coils use superconductors to carry current with negligible electrical resistance. Cryogenic cooling keeps its conductor below the superconducting transition temperature.
Cryotherapy: The medical or wellness use of cold exposure to affect the body. Cryotherapy applies cold; cryogenics studies and produces low temperatures as a technical discipline.
Cryogenic insulation: Materials and structures designed to limit heat transfer into very cold equipment. Reducing heat leaks remains central to lowering cryogen consumption and operating costs.

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