Cryogenics

Cryogenics is the branch of physics and engineering that studies and utilizes materials at extremely low temperatures, typically below 120 kelvin (−153 °C). It involves production, storage, handling, and application of cryogenic fluids such as liquid nitrogen and liquid helium, and the design of devices that reach and maintain very low temperatures.

Key techniques include liquefaction of gases, cryogenic insulation, and refrigeration cycles. Equipment includes Dewar flasks for storage, cryostats for experiments, and cryocoolers for steady cooling. Common temperature scales: Kelvin; primary fluids: helium, hydrogen, neon; widely used liquid nitrogen at 77 K and liquid helium at 4.2 K. Advanced cooling can reach millikelvin ranges with dilution refrigerators.

History: The liquefaction of helium by Heike Kamerlingh Onnes in 1908 enabled the study of matter at low temperatures, followed by the discovery of superconductivity in 1911. Over the 20th century, researchers developed cryostats, vacuum insulation, and staged refrigeration cycles that made practical cryogenics possible.

Applications include medical imaging with MRI, fundamental physics experiments using superconducting magnets, particle accelerators, and spaceflight propulsion with cryogenic propellants. In industry, cryogenics enables materials processing, preservation of biological samples, and cryosurgery.

Safety and environmental considerations center on oxygen deficiency hazards in enclosed spaces, cryogenic burns, pressure risks in stored gases, material embrittlement, and the energy demands of cooling. Helium scarcity and supply security have prompted research into alternative coolants and recycling.