- Buffer gas
A buffer gas is an inert or nonflammable
gas . In theEarth's atmosphere ,nitrogen acts as a buffer gas. A buffer gas addspressure to a system and controls the speed ofcombustion with anyoxygen present. Anyinert gas such ashelium ,neon , orargon will serve as a buffer gas.Uses
Buffer gases are commonly used in many applications from high pressure discharge lamps to reduce line width of
microwave transitions in alkali atoms. A buffer gas usually consists of atomicallyinert gases such ashelium ,argon , andnitrogen which are the primary gases used.Krypton ,neon , andxenon are also used, primarily for lighting. In most scenarios, buffer gases are used in conjunction with othermolecules for the main purpose of causing collisions with the other co-existing molecules.In
fluorescent lamp s, mercury is used as the primaryion from whichlight is emitted. Krypton is the buffer gas used in conjunction with the mercury which is used to moderate the momentum of collisions of mercury ions in order to reduce the damage done to theelectrodes in the fluorescent lamp. Generally speaking, the longest lasting lamps are those with the heaviestnoble gases as buffer gases.Buffer gas loading techniques have been developed for use in cooling paramagnetic atoms and molecules at ultra-cold temperatures. The buffer gas most commonly used in this sort of application is helium. Buffer gas cooling can be used on just about any molecule, as long as the molecule is capable of surviving multiple collisions with low energy helium atoms, which most molecules are capable of doing. Buffer gas cooling is allowing the molecules of interest to be cooled through
elastic collision s with a cold buffer gas inside a chamber (see Figure (a)). If there are enough collisions between the buffer gas and the other molecules of interest before the molecules hit the walls of thechamber and are gone, the buffer gas will sufficiently cool the atoms. There are twoisotopes of helium which are used over He, which are 3He and 4He, that have significantly higher vapor pressures at low temperature which in turn provides the required density of a buffer gas for this procedure.Buffer gases are also commonly used in compressors used in
power plants for supplying gas togas turbines . The buffer gas fills the spaces between seals in the compressor. This space is usually about 2 micrometres wide. The gas must be completely dry and free of anycontaminants . Contaminants can potentially lodge in the space between the seal and cause metal to metal contact in the compressor, leading to compressor failure (above right). In this case the buffer gas acts in a way much like oil does in an automotive engine’sbearings .External links
* [http://cfa-www.harvard.edu/~rkrems/PUBLIC/pra2002b.pdf#search='buffer%20gas' Buffer Gas Cooling]
* [http://ares.ame.arizona.edu/publications/cospar-98.pdf Buffer Gas on Mars]
* [http://www.physics.harvard.edu/Thesespdfs/Egorov.pdf#search='buffer%20gas' Buffer Gas Cooling of Diatomic Molecules]
* [http://tf.nist.gov/ofm/smallclock/buffergas.htm Buffer Gas on Microwave Transition]
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