Buffer gas

Abuffer gasis an inert or nonflammablegas.In theEarth's atmosphere,nitrogenacts as a buffer gas. A buffer gas addspressureto a system and controls the speed ofcombustionwith anyoxygenpresent. Anyinert gassuch ashelium,neon,orargonwill serve as a buffer gas.

A buffer gas usually consists of atomicallyinert gasessuch ashelium,argon,ornitrogen.Krypton,neon,andxenonare also used, primarily for lighting.In most scenarios, buffer gases are used in conjunction with othermoleculesfor the main purpose of causing collisions with the other co-existing molecules.

Buffer gases are commonly used in many applications fromhigh pressure discharge lampsto reduce line width ofmicrowavetransitions inalkali atoms.

Uses

Lighting

Influorescent lamps,mercuryis used as the primaryionfrom whichlightis 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 theelectrodesin the fluorescent lamp. Generally speaking, the longest lasting lamps are those with the heaviestnoble gasesas buffer gases.

Industrial

Buffer gases are also commonly used incompressorsused inpower plantsfor supplying gas togas turbines.The buffer gas fills the spaces betweensealsin 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.In this case the buffer gas acts in a way much like oil does in an automotive engine'sbearings.

Buffer gas cooling

Buffer gas loading techniques have been developed for use in cooling charged orparamagneticatoms 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 (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 thePenning trapor thePaul trap.If the particles are electrically neutral, but paramagnetic, then the trap can be amagnetic trap(as helium is diamagnetic), such as theanti-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.

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 throughelastic collisionswith 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 twoisotopesof helium (³He and⁴He), the rarer³He is sometimes used over⁴He as it provides significantly higher vapor pressures and buffer gas density at sub-kelvin temperatures.

External links

• Buffer Gas Cooling
• Buffer Gas on Mars
• Buffer Gas Cooling of Diatomic Molecules
• Buffer Gas on Microwave Transition