Q-machine
Encyclopedia
A Q-machine is a device that is used in experimental plasma physics.
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 ionisation of atoms of alkali metals
that have low ionisation potentials. The hot plate is made of a
metal that have a large work function 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 or 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
is used instead of an alkaline metal due to its
excellent spectroscopic properties.
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
and at
the University of Iowa
in the USA, at Tohoku University
in Sendai
in Japan, and at the University of Innsbruck in Austria.
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 ionisation of atoms of alkali metals
that have low ionisation potentials. The hot plate is made of a
metal that have a large work function 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 or 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
Barium is a chemical element with the symbol Ba and atomic number 56. It is the fifth element in Group 2, a soft silvery metallic alkaline earth metal. Barium is never found in nature in its pure form due to its reactivity with air. Its oxide is historically known as baryta but it reacts with...
is used instead of an alkaline metal due to its
excellent spectroscopic properties.
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
West Virginia University is a public research university in Morgantown, West Virginia, USA. Other campuses include: West Virginia University at Parkersburg in Parkersburg; West Virginia University Institute of Technology in Montgomery; Potomac State College of West Virginia University in Keyser;...
and at
the University of Iowa
University of Iowa
The University of Iowa is a public state-supported research university located in Iowa City, Iowa, United States. It is the oldest public university in the state. The university is organized into eleven colleges granting undergraduate, graduate, and professional degrees...
in the USA, at Tohoku University
Tohoku University
, abbreviated to , located in the city of Sendai, Miyagi Prefecture in the Tōhoku Region, Japan, is a Japanese national university. It is the third oldest Imperial University in Japan and is a member of the National Seven Universities...
in Sendai
in Japan, and at the University of Innsbruck in Austria.