Editing Buffer gas (section)

== Uses ==

=== Lighting ===
In [[fluorescent lamp]]s, [[Mercury (element)|mercury]] is used as the primary [[ion]] from which [[light]] 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 the [[electrode]]s in the fluorescent lamp.  Generally speaking, the longest lasting lamps are those with the heaviest [[noble gas]]es as buffer gases.{{Citation needed|date=April 2024}}

=== Industrial ===
Buffer gases are also commonly used in [[Gas compressor|compressors]] used in [[power plants]] for supplying gas to [[gas turbines]].  The buffer gas fills the spaces between [[seal (mechanical)|seal]]s in the compressor.  This space is usually about 2 micrometres wide.{{Citation needed|date=April 2024}}  The gas must be completely dry and free of any [[contaminants]].  Contaminants can potentially lodge in the space between the seal and cause metal to metal contact in the compressor, leading to compressor failure.{{Citation needed|date=April 2024}}  In this case the buffer gas acts in a way much like oil does in an automotive engine's [[Bearing (mechanical)|bearings]].

=== Buffer gas cooling ===
Buffer gas loading techniques have been developed for use in cooling charged or [[Paramagnetism|paramagnetic]] atoms and molecules at ultra-cold temperatures. The buffer gas most commonly used in this sort of application is helium.

Suppose we have some very cold helium gas as cryogenic buffer gas, then any cloud of particles floating within that buffer gas would exchange energy with the buffer gas, until it reaches the same temperature ([[Thermalisation|thermalized]]). The problem is that the cloud of particles would diffuse away.

In buffer gas cooling, the cloud of particles we want to cool down is caught in a trap that lets the helium atom pass through. If the particles are electrically charged, then the trap can be the [[Penning trap]] or the [[Quadrupole ion trap|Paul trap]]. If the particles are electrically neutral, but paramagnetic, then the trap can be a [[Magnetic trap (atoms)|magnetic trap]] (as helium is diamagnetic), such as the [[Helmholtz coil|anti-Helmholtz pair]]. Paramagnetic atoms are low-field-seeking while diamagnetic atoms are high-field-seeking, so in a magnetic trap, there is a central region where the magnetic field is zero, rising in all directions. Paramagnetic atoms would be trapped in that zero-field region while the diamagnetic atoms would be repelled away.<ref>{{Cite journal |last=Raizen |first=Mark G. |date=2009-06-12 |title=Comprehensive Control of Atomic Motion |url=https://www.science.org/doi/10.1126/science.1171506 |journal=Science |language=en |volume=324 |issue=5933 |pages=1403–1406 |doi=10.1126/science.1171506 |pmid=19520950 |bibcode=2009Sci...324.1403R |issn=0036-8075|url-access=subscription }}</ref><ref>{{Cite journal |last1=Weinstein |first1=Jonathan D. |last2=deCarvalho |first2=Robert |last3=Guillet |first3=Thierry |last4=Friedrich |first4=Bretislav |last5=Doyle |first5=John M. |date=September 1998 |title=Magnetic trapping of calcium monohydride molecules at millikelvin temperatures |url=https://www.nature.com/articles/25949 |journal=Nature |language=en |volume=395 |issue=6698 |pages=148–150 |doi=10.1038/25949 |bibcode=1998Natur.395..148W |issn=1476-4687|url-access=subscription }}</ref><ref>{{Cite journal |last1=Segev |first1=Yair |last2=Pitzer |first2=Martin |last3=Karpov |first3=Michael |last4=Akerman |first4=Nitzan |last5=Narevicius |first5=Julia |last6=Narevicius |first6=Edvardas |date=August 2019 |title=Collisions between cold molecules in a superconducting magnetic trap |url=https://www.nature.com/articles/s41586-019-1446-2 |journal=Nature |language=en |volume=572 |issue=7768 |pages=189–193 |doi=10.1038/s41586-019-1446-2 |pmid=31391561 |arxiv=1902.04549 |bibcode=2019Natur.572..189S |issn=1476-4687}}</ref>

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.  If there are enough collisions between the buffer gas and the other molecules of interest before the molecules hit the walls of the chamber and are gone, the buffer gas will sufficiently cool the atoms.  Of the two [[isotopes]] of helium (<sup>3</sup>He and <sup>4</sup>He), the rarer <sup>3</sup>He is sometimes used over <sup>4</sup>He as it provides significantly higher vapor pressures and buffer gas density at sub-kelvin temperatures.

{{Citation needed|date=April 2024}}