A Q-machine is a device that is used in experimental

plasma physics Plasma ()πλάσμα
, Henry George Liddell, R ...

. The name Q-machine stems from the original intention of creating a quiescent plasma that is free from the fluctuations that are present in plasmas created in electric discharges. The Q-machine was first described in a publication by Rynn and D'Angelo. The Q-machine plasma is created at a plate that has been heated to about 2000 K and hence is called the hot plate. Electrons are emitted by the hot plate through thermionic emission, and ions are created through contact ionization of atoms of

alkali metals The alkali metals consist of the chemical elements lithium (Li), sodium (Na), potassium (K),The symbols Na and K for sodium and potassium are derived from their Latin names, ''natrium'' and ''kalium''; these are still the origins of the names ...

that have low ionisation potentials. The hot plate is made of a metal that has a large

work function In solid-state physics, the work function (sometimes spelt workfunction) is the minimum thermodynamic work (i.e., energy) needed to remove an electron from a solid to a point in the vacuum immediately outside the solid surface. Here "immediately" ...

and can withstand high temperatures, e.g. tungsten or rhenium. The alkali metal is boiled in an oven that is designed to direct a beam of alkaline metal vapour onto the hot plate. A high value of the hot plate work function and a low ionisation potential of the metal makes for a low potential barrier for an electron in the alkaline metal to overcome, thus making the ionisation process more efficient. Sometimes

barium Barium is a chemical element with the symbol Ba and atomic number 56. It is the fifth element in group 2 and is a soft, silvery alkaline earth metal. Because of its high chemical reactivity, barium is never found in nature as a free element. Th ...

is used instead of an alkaline metal due to its excellent spectroscopic properties. The fractional ionization of a Q-machine plasma can approach unity, which can be orders of magnitude greater than that predicted by the

Saha ionization equation In physics, the Saha ionization equation is an expression that relates the ionization state of a gas in thermal equilibrium to the temperature and pressure. The equation is a result of combining ideas of quantum mechanics and statistical mechanics ...

. The temperature of the Q-machine plasma is close to the temperature of the hot plate, and the ion and electron temperatures are similar. Although this temperature (about 2000 K) is high compared to room temperature, it is much lower than electron temperatures that are usually found in discharge plasma. The low temperature makes it possible to create a plasma column that is several ion gyro radii across. Since the alkaline metals are solids at room temperature they will stick to the walls of the machine on impact, and therefore the neutral pressure can be kept so low that for all practical purposes the plasma is fully ionised. Plasma research that has been performed using Q-machines includes current driven ion cyclotron waves, Kelvin-Helmholtz waves, and electron phase space holes. Today, Q-machines can be found at

West Virginia University West Virginia University (WVU) is a public land-grant research university with its main campus in Morgantown, West Virginia. Its other campuses are those of the West Virginia University Institute of Technology in Beckley, Potomac State College ...

and at the

University of Iowa The University of Iowa (UI, U of I, UIowa, or simply Iowa) is a public university, public research university in Iowa City, Iowa, United States. Founded in 1847, it is the oldest and largest university in the state. The University of Iowa is org ...

in the USA, at

Tohoku University , or is a Japanese national university located in Sendai, Miyagi in the Tōhoku Region, Japan. It is informally referred to as . Established in 1907, it was the third Imperial University in Japan and among the first three Designated National ...

in Sendai in Japan, and at the

University of Innsbruck The University of Innsbruck (german: Leopold-Franzens-Universität Innsbruck; la, Universitas Leopoldino Franciscea) is a public research university in Innsbruck, the capital of the Austrian federal state of Tyrol, founded on October 15, 1669. ...

in Austria.

References

{{Reflist Plasma physics

See also

References