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| {{Other uses|Plasma (disambiguation){{!}}Plasma}}
| | Hello, I'm Jenifer, a 24 year old from Arndorf, Austria.<br>My hobbies include (but are not limited to) Radio-Controlled Car Racing, Gongoozling and watching Arrested Development.<br><br>Feel free to surf to my web-site; [http://v7.wazeo.de/index.php?mod=users&action=view&id=94084 Womens mountain bike sizing.] |
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| {{infobox
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| | title = Plasma
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| | data1 = [[File:Lightning3.jpg|200px]][[File:NeTube.jpg|200px]]
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| | data2 = [[File:Plasma-lamp 2.jpg|200px]][[File:Space Shuttle Atlantis in the sky on July 21, 2011, to its final landing.jpg|200px]]
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| | data3 =Top row: both [[lightning]] and [[electric spark]]s are everyday examples of phenomena made from plasma. [[Neon sign|Neon lights]] could more accurately be called "plasma lights", as the light comes from the plasma inside of them. Bottom row: A [[plasma globe]], illustrating some of the more complex phenomena of a plasma, including ''[[Plasma (physics)#Filamentation|filamentation]]''. The colors are a result of relaxation of electrons in excited states to lower energy states after they have recombined with ions. These processes emit light in a [[spectrum]] characteristic of the gas being excited. The second image is of a plasma trail from [[Space Shuttle Atlantis|Space Shuttle ''Atlantis'']] during re-entry into the [[earth's atmosphere|atmosphere]], as seen from the [[International Space Station]].
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| {{Continuum mechanics}}
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| '''Plasma''' (from [[Greek language|Greek]] πλάσμα, "anything formed"<ref>[http://www.perseus.tufts.edu/hopper/text?doc=Perseus%3Atext%3A1999.04.0057%3Aentry%3Dpla%2Fsma πλάσμα], Henry George Liddell, Robert Scott, ''A Greek-English Lexicon'', on Perseus</ref>) is one of [[State of matter#The Four Fundamental States|the four fundamental states of matter]] (the others being [[solid]], [[liquid]], and [[gas]]). It comprises the major component of the [[Sun]]. Heating a gas may [[ionization|ionize]] its molecules or atoms (reducing or increasing the number of [[electrons]] in them), thus turning it into a plasma, which contains [[charge (physics)|charge]]d particles: positive [[ions]] and negative electrons or ions.<ref>{{cite journal |last1=Luo |first1=Q-Z|last2=D'Angelo|first2=N|last3=Merlino|first3=R. L.| year=1998|title=Shock formation in a negative ion plasma|journal= |volume=5|issue=8|publisher=Department of Physics and Astronomy|url=http://www.physics.uiowa.edu/~rmerlino/nishocks.pdf|accessdate=2011-11-20}}</ref> Ionization can be induced by other means, such as strong electromagnetic field applied with a [[laser]] or [[microwave]] generator, and is accompanied by the dissociation of [[molecular bond]]s, if present.<ref name="Sturrock" /> Plasma can also be created by the application of an electric field on a gas, where the underlying process is the [[Townsend avalanche]].
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| The presence of a non-negligible number of [[charge carrier]]s makes the plasma [[electrical conductivity|electrically conductive]] so that it responds strongly to [[electromagnetic field]]s. Plasma, therefore, has properties quite unlike those of [[solid]]s, [[liquid]]s, or [[gas]]es and is considered a distinct [[state of matter]]. Like gas, plasma does not have a definite shape or a definite volume unless enclosed in a container; unlike gas, under the influence of a magnetic field, it may form structures such as filaments, beams and [[Double layer (plasma)|double layer]]s. Some common plasmas are found in [[star]]s and [[neon sign]]s. In the [[universe]], plasma is the most common [[state of matter]] for [[Baryonic matter|ordinary matter]], most of which is in the rarefied [[Outer space#Intergalactic|intergalactic plasma]] (particularly [[intracluster medium]]) and in stars. Much of the understanding of plasmas has come from the pursuit of controlled [[nuclear fusion]] and [[fusion power]], for which plasma physics provides the scientific basis.
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| ==Properties and parameters==
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| [[File:plasma fountain.gif|thumb|200px|right|Artist's rendition of the Earth's [[plasma fountain]], showing oxygen, helium, and hydrogen ions that gush into space from regions near the Earth's poles. The faint yellow area shown above the north pole represents gas lost from Earth into space; the green area is the [[aurora borealis]], where plasma energy pours back into the atmosphere.<ref>Plasma fountain [http://pwg.gsfc.nasa.gov/istp/news/9812/solar1.html Source], press release: [http://pwg.gsfc.nasa.gov/istp/news/9812/solarwind.html Solar Wind Squeezes Some of Earth's Atmosphere into Space]</ref>]]
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| ===Definition ===
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| Plasma is loosely described as an electrically neutral medium of positive and negative particles (i.e. the overall charge of a plasma is roughly zero). It is important to note that although they are unbound, these particles are not ‘free’. When the charges move they generate electrical currents with magnetic fields, and as a result, they are affected by each other’s fields. This governs their collective behavior with many degrees of freedom.<ref name="Sturrock">{{cite book |title=Plasma Physics: An Introduction to the Theory of Astrophysical, Geophysical & Laboratory Plasmas. |last=Sturrock |first=Peter A. |year=1994 |publisher=Cambridge University Press |isbn=978-0-521-44810-9}}</ref><ref>{{cite book |title=The Framework of Plasma Physics |author=Hazeltine, R.D.; Waelbroeck, F.L. |year=2004 |publisher=Westview Press. |isbn=978-0-7382-0047-7}}
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| </ref> A definition can have three criteria:<ref name="Hazeltine">{{cite book|author=Dendy, R. O. |title=Plasma Dynamics|url=http://books.google.com/?id=S1C6-4OBOeYC|publisher=Oxford University Press|year=1990|isbn=978-0-19-852041-2}}</ref><ref>{{cite book|author=Hastings, Daniel and Garrett, Henry |title=Spacecraft-Environment Interactions|isbn=978-0-521-47128-2|publisher=Cambridge University Press|year=2000}}</ref>
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| #'''The plasma approximation''': Charged particles must be close enough together that each particle influences many nearby charged particles, rather than just interacting with the closest particle (these collective effects are a distinguishing feature of a plasma). The plasma approximation is valid when the number of charge carriers within the sphere of influence (called the ''Debye sphere'' whose radius is the [[Debye length|Debye screening length]]) of a particular particle is higher than unity to provide collective behavior of the charged particles. The average number of particles in the Debye sphere is given by the [[plasma parameter]], "Λ" (the [[Greek alphabet|Greek]] letter [[Lambda]]).
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| #'''Bulk interactions''': The Debye screening length (defined above) is short compared to the physical size of the plasma. This criterion means that interactions in the bulk of the plasma are more important than those at its edges, where boundary effects may take place. When this criterion is satisfied, the plasma is quasineutral.
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| #'''Plasma frequency''': The electron plasma frequency (measuring [[plasma oscillation]]s of the electrons) is large compared to the electron-neutral collision frequency (measuring frequency of collisions between electrons and neutral particles). When this condition is valid, electrostatic interactions dominate over the processes of ordinary gas kinetics.
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| ===Ranges of parameters===
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| Plasma parameters can take on values varying by many [[orders of magnitude]], but the properties of plasmas with apparently disparate parameters may be very similar (see [[plasma scaling]]). The following chart considers only conventional atomic plasmas and not exotic phenomena like [[quark gluon plasma]]s:
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| [[File:Plasma scaling.svg|thumb|250px|'''Range of plasmas'''. Density increases upwards, temperature increases towards the right. The free electrons in a metal may be considered an electron plasma.<ref>{{cite journal|author=Peratt, A. L.|bibcode=1996Ap&SS.242...93P |title=Advances in Numerical Modeling of Astrophysical and Space Plasmas|year=1996|journal=Astrophysics and Space Science|volume=242|issue=1–2|pages=93–163|doi=10.1007/BF00645112}}</ref>]]
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| {| class="wikitable"
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| |+ Typical ranges of plasma parameters: orders of magnitude (OOM)
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| !Characteristic
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| !Terrestrial plasmas
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| !Cosmic plasmas
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| |'''Size'''<br>in meters
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| |10<sup>−6</sup> m (lab plasmas) to<br>10<sup>2</sup> m (lightning) (~8 [[Order of magnitude|OOM]])
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| |10<sup>−6</sup> m (spacecraft sheath) to<br>10<sup>25</sup> m (intergalactic nebula) (~31 OOM)
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| |'''Lifetime'''<br>in seconds
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| |10<sup>−12</sup> s (laser-produced plasma) to<br>10<sup>7</sup> s (fluorescent lights) (~19 OOM)
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| |10<sup>1</sup> s (solar flares) to<br>10<sup>17</sup> s (intergalactic plasma) (~16 OOM)
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| |-
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| |'''Density'''<br> in particles per<br>cubic meter
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| |10<sup>7</sup> m<sup>−3</sup> to<br>10<sup>32</sup> m<sup>−3</sup> (inertial confinement plasma)
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| |1 m<sup>−3</sup> (intergalactic medium) to<br>10<sup>30</sup> m<sup>−3</sup> (stellar core)
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| |-
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| |'''Temperature'''<br>in kelvin
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| |~0 K (crystalline non-neutral plasma<ref>See [http://sdphca.ucsd.edu/ The Nonneutral Plasma Group] at the University of California, San Diego</ref>) to<br>10<sup>8</sup> K (magnetic fusion plasma)
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| |10<sup>2</sup> K (aurora) to<br>10<sup>7</sup> K (solar core)
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| |-
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| |'''Magnetic fields'''<br>in teslas
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| |10<sup>−4</sup> T (lab plasma) to<br>10<sup>3</sup> T (pulsed-power plasma)
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| |10<sup>−12</sup> T (intergalactic medium) to<br>10<sup>11</sup> T (near neutron stars)
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| |}
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| ===Degree of ionization===
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| For plasma to exist, [[ionization]] is necessary. The term "plasma density" by itself usually refers to the "electron density", that is, the number of free electrons per unit volume. The [[degree of ionization]] of a plasma is the proportion of atoms that have lost or gained electrons, and is controlled mostly by the temperature. Even a partially ionized gas in which as little as 1% of the particles are ionized can have the characteristics of a plasma (i.e., response to magnetic fields and high [[electrical conductivity]]). The degree of ionization, ''α'', is defined as ''α'' = ''n''<sub>i</sub>/(''n''<sub>i</sub> + ''n''<sub>a</sub>) where ''n''<sub>i</sub> is the number density of ions and ''n''<sub>a</sub> is the number density of neutral atoms. The ''electron density'' is related to this by the average charge state <Z> of the ions through ''n''<sub>e</sub> = <Z> ''n''<sub>i</sub> where ''n''<sub>e</sub> is the number density of electrons.
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| ===Temperatures===
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| {{see also|Nonthermal plasma}}
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| Plasma temperature is commonly measured in [[kelvin]] or [[electronvolt]]s and is, informally, a measure of the thermal kinetic energy per particle. Very high temperatures are usually needed to sustain ionization, which is a defining feature of a plasma. The degree of plasma ionization is determined by the "electron temperature" relative to the [[ionization energy]] (and more weakly by the density), in a relationship called the [[Saha equation]]. At low temperatures, ions and electrons tend to recombine into bound states—atoms<ref name="Nicholson">{{cite book |title=Introduction to Plasma Theory |last=Nicholson |first= Dwight R. |year=1983 |publisher=John Wiley & Sons |isbn=978-0-471-09045-8}}</ref>—and the plasma will eventually become a gas.
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| In most cases the electrons are close enough to [[thermal equilibrium]] that their temperature is relatively well-defined, even when there is a significant deviation from a [[Maxwell–Boltzmann distribution|Maxwellian]] energy [[distribution function]], for example, due to [[UV radiation]], energetic particles, or strong [[electric fields]]. Because of the large difference in mass, the electrons come to thermodynamic equilibrium amongst themselves much faster than they come into equilibrium with the ions or neutral atoms. For this reason, the "ion temperature" may be very different from (usually lower than) the "[[electron temperature]]". This is especially common in weakly ionized technological plasmas, where the ions are often near the [[ambient temperature]].
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| ====Thermal vs. non-thermal plasmas====
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| Based on the relative temperatures of the electrons, ions and neutrals, plasmas are classified as "thermal" or "non-thermal". Thermal plasmas have electrons and the heavy particles at the same temperature, i.e., they are in thermal equilibrium with each other. Non-thermal plasmas on the other hand have the ions and neutrals at a much lower temperature (sometimes room temperature), whereas electrons are much "hotter" (T<sub>e</sub> >> T<sub>neutrals</sub>).
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| A plasma is sometimes referred to as being "hot" if it is nearly fully ionized, or "cold" if only a small fraction (for example 1%) of the gas molecules are ionized, but other definitions of the terms "hot plasma" and "cold plasma" are common. Even in a "cold" plasma, the electron temperature is still typically several thousand degrees Celsius. Plasmas utilized in "plasma technology" ("technological plasmas") are usually cold plasmas in the sense that only a small fraction of the gas molecules are ionized.
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| ===Potentials===
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| [[File:Lightning over Oradea Romania 3.jpg|thumb|300px|right|[[Lightning]]
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| is an example of plasma present at Earth's surface.
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| Typically, lightning discharges 30,000 amperes at up to 100 million volts, and emits light, radio waves, X-rays and even gamma rays.<ref>See [http://www.nasa.gov/vision/universe/solarsystem/rhessi_tgf.html Flashes in the Sky: Earth's Gamma-Ray Bursts Triggered by Lightning]</ref> Plasma temperatures in lightning can approach 28,000 kelvin and electron densities may exceed 10<sup>24</sup> m<sup>−3</sup>.]]
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| Since plasmas are very good [[electrical conductor]]s, electric potentials play an important role.
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| The potential as it exists on average in the space between charged particles, independent of the question of how it can be measured, is called the "plasma potential", or the "space potential". If an electrode is inserted into a plasma, its potential will generally lie considerably below the plasma potential due to what is termed a [[Debye sheath]]. The good electrical conductivity of plasmas makes their electric fields very small. This results in the important concept of "quasineutrality", which says the density of negative charges is approximately equal to the density of positive charges over large volumes of the plasma (''n''<sub>e</sub> = <Z>''n''<sub>i</sub>), but on the scale of the Debye length there can be charge imbalance. In the special case that ''[[Double layer (plasma)|double layers]]'' are formed, the charge separation can extend some tens of Debye lengths.
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| The magnitude of the potentials and electric fields must be determined by means other than simply finding the net [[charge density]]. A common example is to assume that the electrons satisfy the [[Boltzmann relation]]:
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| :<math>n_e \propto e^{e\Phi/k_BT_e}.</math>
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| Differentiating this relation provides a means to calculate the electric field from the density:
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| :<math>\vec{E} = (k_BT_e/e)(\nabla n_e/n_e).</math>
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| It is possible to produce a plasma that is not quasineutral. An electron beam, for example, has only negative charges. The density of a non-neutral plasma must generally be very low, or it must be very small, otherwise it will be dissipated by the repulsive [[electrostatic force]].
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| In [[astrophysical]] plasmas, [[electric field screening|Debye screening]] prevents [[electric field]]s from directly affecting the plasma over large distances, i.e., greater than the [[Debye length]]. However, the existence of charged particles causes the plasma to generate and can be affected by [[magnetic field]]s. This can and does cause extremely complex behavior, such as the generation of plasma double layers, an object that separates charge over a few tens of [[Debye length]]s. The dynamics of plasmas interacting with external and self-generated [[magnetic field]]s are studied in the [[academic discipline]] of [[magnetohydrodynamics]].
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| ===Magnetization===
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| Plasma with a magnetic field strong enough to influence the motion of the charged particles is said to be magnetized. A common quantitative criterion is that a particle on average completes at least one gyration around the magnetic field before making a collision, i.e., ω<sub>ce</sub>/ν<sub>coll</sub> > 1, where ω<sub>ce</sub> is the "electron gyrofrequency" and ν<sub>coll</sub> is the "electron collision rate". It is often the case that the electrons are magnetized while the ions are not. Magnetized plasmas are ''[[anisotropic]]'', meaning that their properties in the direction parallel to the magnetic field are different from those perpendicular to it. While electric fields in plasmas are usually small due to the high conductivity, the electric field associated with a plasma moving in a magnetic field is given by '''E''' = −'''v''' × '''B''' (where '''E''' is the electric field, '''v''' is the velocity, and '''B''' is the magnetic field), and is not affected by [[Debye shielding]].<ref>Richard Fitzpatrick, ''Introduction to Plasma Physics'', [http://farside.ph.utexas.edu/teaching/plasma/lectures/node10.html Magnetized plasmas]</ref>
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| ===Comparison of plasma and gas phases===
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| Plasma is often called the ''fourth state of matter'' after solid, liquids and gases.<ref>Yaffa Eliezer, Shalom Eliezer, ''The Fourth State of Matter: An Introduction to the Physics of Plasma'', Publisher: Adam Hilger, 1989, ISBN 978-0-85274-164-1, 226 pages, page 5</ref><ref>{{cite book|author=Bittencourt, J.A.|title=Fundamentals of Plasma Physics|publisher=Springer|year=2004|isbn=9780387209753|page=1|url=http://books.google.com/books?id=qCA64ys-5bUC&pg=PA1}}</ref> It is distinct from these and other lower-energy [[states of matter]]. Although it is closely related to the gas phase in that it also has no definite form or volume, it differs in a number of ways, including the following:
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| {| class="wikitable"
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| ! Property !! Gas !! Plasma
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| ! [[Electrical resistivity and conductivity|Electrical conductivity]]
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| | '''Very low''': Air is an excellent insulator until it breaks down into plasma at electric field strengths above 30 kilovolts per centimeter.<ref>{{cite web|url=http://hypertextbook.com/facts/2000/AliceHong.shtml|title=Dielectric Strength of Air|year=2000|first=Alice|last=Hong|work=The Physics Factbook}}</ref>
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| | '''Usually very high''': For many purposes, the conductivity of a plasma may be treated as infinite.
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| ! Independently acting species
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| | '''One''': All gas particles behave in a similar way, influenced by [[gravity]] and by [[collision]]s with one another.
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| | '''Two or three''': [[Electron]]s, [[ion]]s, [[proton]]s and [[neutron]]s can be distinguished by the sign and value of their [[electric charge|charge]] so that they behave independently in many circumstances, with different bulk velocities and temperatures, allowing phenomena such as new types of [[waves in plasma|waves]] and [[Instability|instabilities]].
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| ! Velocity distribution
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| | '''[[Maxwell–Boltzmann distribution|Maxwellian]]''': Collisions usually lead to a Maxwellian velocity distribution of all gas particles, with very few relatively fast particles.
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| | '''Often non-Maxwellian''': Collisional interactions are often weak in hot plasmas and external forcing can drive the plasma far from local equilibrium and lead to a significant population of unusually fast particles.
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| ! Interactions
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| | '''Binary''': Two-particle collisions are the rule, three-body collisions extremely rare.
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| | '''Collective''': Waves, or organized motion of plasma, are very important because the particles can interact at long ranges through the electric and magnetic forces.
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| |}
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| ==Common plasmas==
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| {{further|Astrophysical plasma|Interstellar medium|Intergalactic space}}
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| Plasmas are by far the most common [[Phase (matter)|phase of ordinary matter]] in the universe, both by mass and by volume.<ref>It is often stated that more than 99% of the material in the visible universe is plasma. See, for example, {{cite book|author=Gurnett, D. A. and Bhattacharjee, A. |title=Introduction to Plasma Physics: With Space and Laboratory Applications|year=2005|url=http://books.google.com/?id=VcueZlunrbcC&pg=PA2|page=2|isbn=978-0-521-36483-6|publisher=Cambridge University Press|location=Cambridge, UK}} and {{cite book|author=Scherer, K; Fichtner, H and Heber, B |title=Space Weather: The Physics Behind a Slogan|year=2005|url=http://books.google.com/?id=irHgIUtLi0gC&pg=PA138|page=138|isbn=978-3-540-22907-0|publisher=Springer|location=Berlin}}. Essentially, all of the visible light from space comes from stars, which are plasmas with a temperature such that they radiate strongly at visible wavelengths. Most of the ordinary (or [[baryon]]ic) matter in the universe, however, is found in the [[Outer space#Intergalactic|intergalactic medium]], which is also a plasma, but much hotter, so that it radiates primarily as X-rays. The current scientific consensus is that about 96% of the total energy density in the universe is not plasma or any other form of ordinary matter, but a combination of [[cold dark matter]] and [[dark energy]].</ref> Our Sun, and all [[star]]s, are made of plasma, much of [[Interstellar medium|interstellar space]] is filled with a plasma, albeit a very sparse one, and [[Outer space#Intergalactic|intergalactic space]] too. In our solar system, [[interplanetary space]] is filled with the plasma of the [[Solar Wind]] that extends from the Sun out to the [[Heliopause (astronomy)#Heliopause|heliopause]]. Even [[black holes]], which are not directly visible, are fuelled by accreting ionising matter (i.e. plasma),<ref>Mészáros, Péter (2010) ''The High Energy Universe: Ultra-High Energy Events in Astrophysics and Cosmology'', Publisher Cambridge University Press, ISBN 978-0-521-51700-3, [http://books.google.com/books?id=NXvE_zQX5kAC&lpg=PA99&dq=%22Black%20hole%22%20plasma%20acreting&pg=PA99 p. 99].</ref> and they are associated with astrophysical jets of luminous ejected plasma,<ref>Raine, Derek J. and Thomas, Edwin George (2010) ''Black Holes: An Introduction'', Publisher: Imperial College Press, ISBN 978-1-84816-382-9, [http://books.google.com/books?id=O3puAMw5U3UC&lpg=PA160 p. 160]</ref> such as [[Messier 87#Jet|M87's jet]] that extends 5,000 light-years.<ref>Nemiroff, Robert and Bonnell, Jerry (11 December 2004) [http://apod.nasa.gov/apod/ap041211.html Astronomy Picture of the Day], nasa.gov</ref>
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| Dust and small grains within a plasma will also pick up a net negative charge, so that they in turn may act like a very heavy negative ion component of the plasma (see [[dusty plasma]]s).
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| The current consensus is that about 96% of the total energy density in the universe is not plasma or any other form of ordinary matter, but a combination of [[cold dark matter]] and [[dark energy]]. In our Solar System, however, the density of ordinary matter is much higher than average and much higher than that of either dark matter or dark energy. The planet [[Jupiter]] accounts for most of the ''non''-plasma, only about 0.1% of the mass and 10<sup>−15</sup>% of the volume within the orbit of [[Pluto]].
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| {{clear}}
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| {| class="wikitable"
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| |+ Common forms of plasma
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| ! style="width: auto;"|Artificially produced
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| ! style="width: auto;"|[[Earth|Terrestrial]] plasmas
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| ! style="width: auto;"|Space and [[Astrophysics|astrophysical]] plasmas
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| |- style="vertical-align: top;"
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| *Those found in [[plasma displays]], including TVs
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| *Inside [[fluorescent lamp]]s (low energy lighting), [[neon sign]]s<ref>[http://ippex.pppl.gov/fusion/glossary.html IPPEX Glossary of Fusion Terms]. Ippex.pppl.gov. Retrieved on 2011-11-19.</ref>
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| *Rocket exhaust and [[ion thruster]]s
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| *The area in front of a [[spacecraft]]'s [[heat shield]] during re-entry into the [[earth's atmosphere|atmosphere]]
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| *Inside a corona discharge [[ozone]] generator
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| *[[Fusion energy]] research
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| *The [[electric arc]] in an [[arc lamp]], an arc [[welding|welder]] or [[plasma torch]]
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| *Plasma ball (sometimes called a plasma sphere or [[plasma globe]])
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| *Arcs produced by [[Tesla coil]]s (resonant air core transformer or disruptor coil that produces arcs similar to lightning, but with [[alternating current]] rather than [[static electricity]])
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| *Plasmas used in [[semiconductor device fabrication]] including [[reactive-ion etching]], [[sputtering]], [[Plasma cleaning|surface cleaning]] and [[plasma-enhanced chemical vapor deposition]]
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| *[[Laser]]-produced plasmas (LPP), found when high power lasers interact with materials.
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| *[[Inductively coupled plasma]]s (ICP), formed typically in [[argon]] gas for optical emission [[spectroscopy]] or [[mass spectrometry]]
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| *Magnetically induced plasmas (MIP), typically produced using microwaves as a resonant coupling method
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| *[[Static electricity|Static electric sparks]]
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| *[[Lightning]]
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| *[[St. Elmo's fire]]
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| *[[Upper-atmospheric lightning]] (e.g. Blue jets, Blue starters, Gigantic jets, ELVES)
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| *[[Sprite (lightning)|Sprites]]
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| *The [[ionosphere]]
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| *The [[plasmasphere]]
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| *The [[Aurora (astronomy)|polar aurorae]]
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| *Some [[flame]]s<ref>"[http://www.plasmacoalition.org/plasma_writeups/flame.pdf Plasma and Flames – The Burning Question]", from the Coalition for Plasma Science, retrieved 8 November 2012</ref><ref>von Engel, A. and Cozens, J.R. (1976) "Flame Plasma" in ''Advances in electronics and electron physics'', L. L. Marton (ed.), Academic Press, ISBN 978-0-12-014520-1, [http://books.google.com/books?id=0Mndi2cCMuUC&lpg=PA99 p. 99]</ref>
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| *The [[polar wind]], a plasma fountain
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| *The [[Sun]] and other [[star]]s<br />(plasmas heated by [[nuclear fusion]])
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| *The [[solar wind]]
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| *The [[interplanetary medium]]<br />(space between planets)
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| *The [[interstellar medium]]<br />(space between star systems)
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| *The [[Outer space#Intergalactic|Intergalactic medium]]<br />(space between galaxies)
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| *The [[Io (moon)|Io]]-[[Jupiter]] [[flux tube]]
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| *[[Accretion disc]]s
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| *Interstellar [[nebula]]e
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| *[[Comet tail|Cometary ion tail]]
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| |}
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| ==Complex plasma phenomena==
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| Although the underlying equations governing plasmas are relatively simple, plasma behavior is extraordinarily varied and subtle: the emergence of unexpected behavior from a simple model is a typical feature of a [[complex system]]. Such systems lie in some sense on the boundary between ordered and disordered behavior and cannot typically be described either by simple, smooth, mathematical functions, or by pure randomness. The spontaneous formation of interesting spatial features on a wide range of length scales is one manifestation of plasma complexity. The features are interesting, for example, because they are very sharp, spatially intermittent (the distance between features is much larger than the features themselves), or have a [[fractal]] form. Many of these features were first studied in the laboratory, and have subsequently been recognized throughout the universe. Examples of complexity and complex structures in plasmas include:
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| ===Filamentation===
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| Striations or string-like structures,<ref>{{cite journal|author=Dickel, J. R.|bibcode=1990BAAS...22..832D |title=The Filaments in Supernova Remnants: Sheets, Strings, Ribbons, or?|year=1990|journal=Bulletin of the American Astronomical Society|volume= 22|page=832}}</ref> also known as [[birkeland current]]s, are seen in many plasmas, like the [[plasma globe|plasma ball]], the [[Aurora (astronomy)|aurora]],<ref>{{cite doi|10.1029/2002GL016362}}</ref> [[lightning]],<ref>{{cite doi|10.1029/2005JA011350}}</ref> [[electric arc]]s, [[solar flares]],<ref>{{cite journal|author=Doherty, Lowell R.|doi=10.1086/148107|title=Filamentary Structure in Solar Prominences|year=1965|journal=The Astrophysical Journal|volume=141|page=251|last2=Menzel|first2=Donald H.|bibcode=1965ApJ...141..251D}}</ref> and [[supernova remnant]]s.<ref>[http://web.archive.org/web/20091005084515/http://seds.lpl.arizona.edu/messier/more/m001_hst.html Hubble views the Crab Nebula M1: The Crab Nebula Filaments]. The University of Arizona</ref> They are sometimes associated with larger current densities, and the interaction with the magnetic field can form a [[magnetic rope]] structure.<ref>{{cite doi|10.1016/S0275-1062(02)00095-4}}</ref> High power microwave breakdown at atmospheric pressure also leads to the formation of filamentary structures.<ref name="mwbrkdwn">{{cite doi|10.1103/PhysRevLett.104.015002}}</ref> (See also [[Plasma pinch]])
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| Filamentation also refers to the self-focusing of a high power laser pulse. At high powers, the nonlinear part of the index of refraction becomes important and causes a higher index of refraction in the center of the laser beam, where the laser is brighter than at the edges, causing a feedback that focuses the laser even more. The tighter focused laser has a higher peak brightness (irradiance) that forms a plasma. The plasma has an index of refraction lower than one, and causes a defocusing of the laser beam. The interplay of the focusing index of refraction, and the defocusing plasma makes the formation of a long filament of plasma that can be [[micrometer (unit)|micrometers]] to kilometers in length.<ref>{{cite journal|author=Chin, S. L. |url=http://icpr.snu.ac.kr/resource/wop.pdf/J01/2006/049/S01/J012006049S010281.pdf|journal=Journal of the Korean Physical Society|volume=49|year=2006|page=281|title=Some Fundamental Concepts of Femtosecond Laser Filamentation}}</ref> One interesting aspect of the filamentation generated plasma is the relatively low ion density due to defocusing effects of the ionized electrons.<ref>{{cite doi|10.1016/S0030-4018(00)00903-2}}</ref> (See also [[Filament propagation]])
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| ===Shocks or double layers===
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| Plasma properties change rapidly (within a few [[Debye length]]s) across a two-dimensional sheet in the presence of a (moving) shock or (stationary) [[Double layer (plasma)|double layer]]. Double layers involve localized charge separation, which causes a large potential difference across the layer, but does not generate an electric field outside the layer. Double layers separate adjacent plasma regions with different physical characteristics, and are often found in current carrying plasmas. They accelerate both ions and electrons.
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| ===Electric fields and circuits===
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| Quasineutrality of a plasma requires that plasma currents close on themselves in electric circuits. Such circuits follow [[Kirchhoff's circuit laws]] and possess a [[Electrical resistance|resistance]] and [[inductance]]. These circuits must generally be treated as a strongly coupled system, with the behavior in each plasma region dependent on the entire circuit. It is this strong coupling between system elements, together with nonlinearity, which may lead to complex behavior. Electrical circuits in plasmas store inductive (magnetic) energy, and should the circuit be disrupted, for example, by a plasma instability, the inductive energy will be released as plasma heating and acceleration. This is a common explanation for the heating that takes place in the [[solar corona]]. Electric currents, and in particular, magnetic-field-aligned electric currents (which are sometimes generically referred to as "[[Birkeland current]]s"), are also observed in the Earth's aurora, and in plasma filaments.
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| ===Cellular structure===
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| Narrow sheets with sharp gradients may separate regions with different properties such as magnetization, density and temperature, resulting in cell-like regions. Examples include the [[magnetosphere]], [[heliosphere]], and [[heliospheric current sheet]]. [[Hannes Alfvén]] wrote: "From the cosmological point of view, the most important new space research discovery is probably the cellular structure of space. As has been seen in every region of space accessible to in situ measurements, there are a number of 'cell walls', sheets of electric currents, which divide space into compartments with different magnetization, temperature, density, etc."<ref>{{cite book|author=Alfvén, Hannes |title=Cosmic Plasma|year=1981|chapter=section VI.13.1. Cellular Structure of Space|isbn=978-90-277-1151-9|publisher=Dordrecht}}</ref>
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| ===Critical ionization velocity===
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| The [[critical ionization velocity]] is the relative velocity between an ionized plasma and a neutral gas, above which a runaway ionization process takes place. The critical ionization process is a quite general mechanism for the conversion of the kinetic energy of a rapidly streaming gas into ionization and plasma thermal energy. Critical phenomena in general are typical of complex systems, and may lead to sharp spatial or temporal features.
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| ===Ultracold plasma===
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| Ultracold plasmas are created in a [[magneto-optical trap]] (MOT) by trapping and cooling neutral [[atoms]], to temperatures of 1 [[millikelvin|mK]] or lower, and then using another [[laser]] to [[ionize]] the atoms by giving each of the outermost electrons just enough energy to escape the electrical attraction of its parent ion.
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| One advantage of ultracold plasmas are their well characterized and tunable initial conditions, including their size and electron temperature. By adjusting the wavelength of the ionizing laser, the kinetic energy of the liberated electrons can be tuned as low as 0.1 K, a limit set by the frequency bandwidth of the laser pulse. The ions inherit the millikelvin temperatures of the neutral atoms, but are quickly heated through a process known as disorder induced heating (DIH). This type of non-equilibrium ultracold plasma evolves rapidly, and displays many other interesting phenomena.<ref>{{cite book|url=http://books.google.com/?id=rHo6IbakG2kC&pg=PA190|pages=190–193|title=Plasma science: advancing knowledge in the national interest|author=National Research Council (U.S.). Plasma 2010 Committee|publisher=National Academies Press|year=2007|isbn=978-0-309-10943-7}}</ref>
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| One of the metastable states of a strongly nonideal plasma is [[Rydberg matter]], which forms upon condensation of excited atoms.
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| ===[[Non-neutral plasmas|Non-neutral plasma]]===
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| The strength and range of the electric force and the good conductivity of plasmas usually ensure that the densities of positive and negative charges in any sizeable region are equal ("quasineutrality"). A plasma with a significant excess of charge density, or, in the extreme case, is composed of a single species, is called a [[Non-neutral plasmas|non-neutral plasma]]. In such a plasma, electric fields play a dominant role. Examples are charged [[particle beam]]s, an electron cloud in a [[Penning trap]] and positron plasmas.<ref>{{cite doi|10.1063/1.870693}}</ref>
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| ===Dusty plasma and grain plasma===
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| A [[dusty plasma]] contains tiny charged particles of dust (typically found in space). The dust particles acquire high charges and interact with each other. A plasma that contains larger particles is called grain plasma. Under laboratory conditions, dusty plasmas are also called ''complex plasmas''.<ref>{{cite journal |last=Morfill |first=G. E. |title= Complex plasmas: An interdisciplinary research field |journal=Review of Modern Physics |volume=81 |year=2009 |pages=1353–1404 |doi=10.1103/RevModPhys.81.1353|bibcode = 2009RvMP...81.1353M |first2=Alexei |issue=4 }}</ref>
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| ===Impermeable plasma===
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| Impermeable plasma is a type of thermal plasma which acts like an impermeable solid with respect to gas or cold plasma and can be physically pushed. Interaction of cold gas and thermal plasma was briefly studied by a group led by [[Hannes Alfvén]] in 1960s and 1970s for its possible applications in insulation of [[Nuclear fusion|fusion]] plasma from the reactor walls.<ref>{{cite journal |last1=Alfvén |first1=H. |last2=Smårs |first2=E.|title= Gas-Insulation of a Hot Plasma |journal=Nature |volume=188 |year=1960 |pages=801–802 |doi=10.1038/188801a0|bibcode = 1960Natur.188..801A |issue=4753 }}</ref> However later it was found that the external [[magnetic fields]] in this configuration could induce [[kink instabilities]] in the plasma and subsequently lead to an unexpectedly high heat loss to the walls.<ref>{{cite journal |last1=Braams |first1=C.M. |title= Stability of Plasma Confined by a Cold-Gas Blanket |journal=Physical Review Letters |volume=17 |issue=9 |year=1966 |pages=470–471 |doi=10.1103/PhysRevLett.17.470|bibcode = 1966PhRvL..17..470B }}</ref>
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| In 2013, a group of materials scientists reported that they have successfully generated stable impermeable plasma with no [[magnetic confinement]] using only an ultrahigh-pressure blanket of cold gas. While spectroscopic data on the characteristics of plasma were claimed to be difficult to obtain due to the high-pressure, the passive effect of plasma on [[Chemical synthesis|synthesis]] of different [[nanostructures]] clearly suggested the effective confinement. They also showed that upon maintaining the impermeability for a few tens of seconds, screening of [[ions]] at the plasma-gas interface could give rise to a strong secondary mode of heating (known as viscous heating) leading to different kinetics of reactions and formation of complex [[nanomaterials]].<ref>{{cite journal |last1=Yaghoubi |first1=A. |last2=Mélinon |first2=P.|title= Tunable synthesis and in situ growth of silicon-carbon mesostructures using impermeable plasma |journal=Scientific Reports |volume=3 |year=2013 |doi=10.1038/srep01083|bibcode = 2013NatSR...3E1083Y }}</ref>
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| ==Mathematical descriptions==
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| [[File:Magnetic rope.svg|thumb|The complex self-constricting magnetic field lines and current paths in a field-aligned [[Birkeland current]] that can develop in a plasma.<ref>See [http://history.nasa.gov/SP-345/ch15.htm#250 Evolution of the Solar System]'', 1976)''</ref>]]
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| {{main|Plasma modeling}}
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| To completely describe the state of a plasma, we would need to write down all the
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| particle locations and velocities and describe the electromagnetic field in the plasma region.
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| However, it is generally not practical or necessary to keep track of all the particles in a plasma.
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| Therefore, plasma physicists commonly use less detailed descriptions, of which
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| there are two main types:
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| ===Fluid model===
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| Fluid models describe plasmas in terms of smoothed quantities, like density and averaged velocity around each position (see [[Plasma parameters]]). One simple fluid model, [[magnetohydrodynamics]], treats the plasma as a single fluid governed by a combination of [[Maxwell's equations]] and the [[Navier–Stokes equations]]. A more general description is the [[two-fluid plasma]] picture, where the ions and electrons are described separately. Fluid models are often accurate when collisionality is sufficiently high to keep the plasma velocity distribution close to a [[Maxwell–Boltzmann distribution]]. Because fluid models usually describe the plasma in terms of a single flow at a certain temperature at each spatial location, they can neither capture velocity space structures like beams or [[Double layer (plasma)|double layer]]s, nor resolve wave-particle effects.
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| ===Kinetic model===
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| Kinetic models describe the particle velocity distribution function at each point in the plasma and therefore do not need to assume a [[Maxwell–Boltzmann distribution]]. A kinetic description is often necessary for collisionless plasmas. There are two common approaches to kinetic description of a plasma. One is based on representing the smoothed distribution function on a grid in velocity and position. The other, known as the [[particle-in-cell]] (PIC) technique, includes kinetic information by following the trajectories of a large number of individual particles. Kinetic models are generally more computationally intensive than fluid models. The [[Vlasov equation]] may be used to describe the dynamics of a system of charged particles interacting with an electromagnetic field.
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| In magnetized plasmas, a [[gyrokinetics|gyrokinetic]] approach can substantially reduce the computational expense of a fully kinetic simulation.
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| ==Artificial plasmas==
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| Most artificial plasmas are generated by the application of electric and/or magnetic fields. Plasma generated in a laboratory setting and for industrial use can be generally categorized by:
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| *The type of power source used to generate the plasma—DC, RF and microwave
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| *The pressure they operate at—vacuum pressure (< 10 mTorr or 1 Pa), moderate pressure (~ 1 Torr or 100 Pa), atmospheric pressure (760 Torr or 100 kPa)
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| *The degree of ionization within the plasma—fully, partially, or weakly ionized
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| *The temperature relationships within the plasma—thermal plasma (''T<sub>e</sub>'' = ''T''<sub>ion</sub> = ''T''<sub>gas</sub>), non-thermal or "cold" plasma (''T<sub>e</sub>'' >> ''T''<sub>ion</sub> = ''T''<sub>gas</sub>)
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| *The electrode configuration used to generate the plasma
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| *The magnetization of the particles within the plasma—magnetized (both ion and electrons are trapped in [[Gyroradius|Larmor orbits]] by the magnetic field), partially magnetized (the electrons but not the ions are trapped by the magnetic field), non-magnetized (the magnetic field is too weak to trap the particles in orbits but may generate [[Lorentz force]]s)
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| *The application.
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| ===Generation of artificial plasma===
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| [[File:Plasma jacobs ladder.jpg|thumb|alt=Artificial plasma produced in air by a Jacob's Ladder|Artificial plasma produced in air by a [[Spark gap#Visual entertainment|Jacob's Ladder]]]]
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| Just like the many uses of plasma, there are several means for its generation, however, one principle is common to all of them: there must be energy input to produce and sustain it.<ref name="Hippler" /> For this case, plasma is generated when an [[electric current|electrical current]] is applied across a [[dielectric gas]] or fluid (an electrically [[Electrical conductor|non-conducting]] material) as can be seen in the image below, which shows a [[discharge tube]] as a simple example ([[direct current|DC]] used for simplicity).
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| [[File:Simple representation of a discharge tube - plasma.png|Simple representation of a DC discharge tube.]]
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| [[File:Cascade-process-of-ionization.svg|thumb|Cascade process of ionization. Electrons are ‘e−’, neutral atoms ‘o’, and cations ‘+’.]]
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| [[Image:Electron avalanche.gif|thumbnail|left|300px|Avalanche effect between two electrodes. The original ionisation event liberates one electron, and each subsequent collision liberates a further electron, so two electrons emerge from each collision: the ionising electron and the liberated electron.]]
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| The [[potential difference]] and subsequent [[electric field]] pull the bound electrons (negative) toward the [[anode]] (positive electrode) while the [[cathode]] (negative electrode) pulls the nucleus.<ref name="Chen">{{cite book |title=Plasma Physics and Controlled Fusion |last=Chen |first=Francis F. |year=1984 |publisher=Plenum Press |isbn=978-0-306-41332-2}}</ref> As the [[voltage]] increases, the current stresses the material (by [[electric polarization]]) beyond its [[dielectric strength|dielectric limit]] (termed strength) into a stage of [[electrical breakdown]], marked by an [[electric spark]], where the material transforms from being an [[insulator (electrical)|insulator]] into a [[Electrical conductor|conductor]] (as it becomes increasingly [[ionized]]). The underlying process is the [[Townsend avalanche]], where collisions between electrons and neutral gas atoms create more ions and electrons (as can be seen in the figure on the right). The first impact of an electron on an atom results in one ion and two electrons. Therefore, the number of charged particles increases rapidly (in the millions) only “after about 20 successive sets of collisions”,<ref name="Leal-Quiros" /> mainly due to a small mean free path (average distance travelled between collisions).
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| ====Electric arc====
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| With ample current density and ionization, this forms a luminous [[electric arc]] (a continuous electric discharge similar to [[lightning]]) between the electrodes.{{#tag:ref|The material undergoes various ‘regimes’ or stages (e.g. saturation, breakdown, glow, transition and thermal arc) as the voltage is increased under the voltage-current relationship. The voltage rises to its maximum value in the saturation stage, and thereafter it undergoes fluctuations of the various stages; while the current progressively increases throughout.<ref name="Leal-Quiros">{{cite journal |author=Leal-Quirós, Edbertho |year=2004 |title=Plasma Processing of Municipal Solid Waste |journal= Brazilian Journal of Physics |volume=34 |issue=4B |page=1587 |bibcode = 2004BrJPh..34.1587L |doi=10.1590/S0103-97332004000800015}}</ref>|group="Note"}} [[Electrical resistance]] along the continuous electric arc creates [[heat]], which dissociates more gas molecules and ionizes the resulting atoms (where degree of ionization is determined by temperature), and as per the sequence: [[solid]]-[[liquid]]-[[gas]]-plasma, the gas is gradually turned into a thermal plasma.{{#tag:ref|Across literature, there appears to be no strict definition on where the boundary is between a gas and plasma. Nevertheless, it is enough to say that at 2000°C the gas molecules become atomized, and ionized at 3000°C and "in this state, [the] gas has a liquid like viscosity at atmospheric pressure and the free electric charges confer relatively high electrical conductivities that can approach those of metals.”<ref name="Gomez" />|group="Note"}} A thermal plasma is in [[thermal equilibrium]], which is to say that the temperature is relatively homogeneous throughout the heavy particles (i.e. atoms, molecules and ions) and electrons. This is so because when thermal plasmas are generated, [[electrical energy]] is given to electrons, which, due to their great mobility and large numbers, are able to disperse it rapidly and by [[elastic collision]] (without energy loss) to the heavy particles.<ref name="Gomez" /><ref group="Note">Note that non-thermal, or non-equilibrium plasmas are not as ionized and have lower energy densities, and thus the temperature is not dispersed evenly among the particles, where some heavy ones remain ‘cold’.</ref>
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| ===Examples of industrial/commercial plasma===
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| Because of their sizable temperature and density ranges, plasmas find applications in many fields of research, technology and industry. For example, in: industrial and extractive [[metallurgy]],<ref name="Gomez">{{cite doi|10.1016/j.jhazmat.2008.04.017}}</ref> surface treatments such as [[plasma spraying]] (coating), [[etching]] in microelectronics,<ref name="NRC">{{cite book |author= National Research Council |year=1991 |title=Plasma Processing of Materials : Scientific Opportunities and Technological Challenges. |publisher=National Academies Press |isbn= 978-0-309-04597-1}}</ref> metal cutting<ref name="Nemchinsky">{{cite doi|10.1088/0022-3727/39/22/R01}}</ref> and [[welding]]; as well as in everyday [[Vehicle emissions control|vehicle exhaust cleanup]] and [[Fluorescent lamp|fluorescent]]/[[Electroluminescence|luminescent]] lamps,<ref name="Hippler">{{cite book |editor=Hippler, R., Kersten, H., Schmidt, M., Schoenbach, K.M. |year=2008 |title=Low Temperature Plasmas: Fundamentals, Technologies, and Techniques |chapter=Plasma Sources |publisher=Wiley-VCH |edition=2 |isbn=978-3-527-40673-9}}</ref> while even playing a part in [[Scramjet|supersonic combustion engines]] for [[aerospace engineering]].<ref name="Peretich">{{cite journal |author=Peretich, M.A., O’Brien, W.F., Schetz, J.A. |year=2007 |title=Plasma torch power control for scramjet application |publisher=Virginia Space Grant Consortium |url=http://www.vsgc.odu.edu/src/SRC07/SRC07papers/Mark%20Peretich%20_%20PaperFinal%20Report.pdf |accessdate=12 April 2010}}</ref>
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| ====Low-pressure discharges====
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| *''[[Glow discharge]] plasmas'': non-thermal plasmas generated by the application of DC or low frequency RF (<100 kHz) electric field to the gap between two metal electrodes. Probably the most common plasma; this is the type of plasma generated within [[fluorescent light]] tubes.<ref>{{cite web |url=http://www-spof.gsfc.nasa.gov/Education/wfluor.html |title=The Fluorescent Lamp: A plasma you can use. |author= Stern, David P. |accessdate=2010-05-19}}</ref>
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| *''[[Capacitively coupled plasma]] (CCP)'': similar to glow discharge plasmas, but generated with high frequency RF electric fields, typically [[ISM band|13.56 MHz]]. These differ from glow discharges in that the sheaths are much less intense. These are widely used in the microfabrication and integrated circuit manufacturing industries for plasma etching and plasma enhanced chemical vapor deposition.<ref>{{cite journal |last1=Sobolewski |first1=M.A. |last2=Langan & Felker |first2=J.G. & B.S. |year=1997 |title=Electrical optimization of plasma-enhanced chemical vapor deposition chamber cleaning plasmas |publisher=Journal of Vacuum Science and Technology B |volume=16 |issue=1 |pages=173–182 |url=http://physics.nist.gov/MajResProj/rfcell/Publications/MAS_JVSTB16_1.pdf}}</ref>
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| *''[[Cascaded Arc Plasma Source]]'': a device to produce low temperature (~1eV) high density plasmas.
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| *''[[Inductively coupled plasma]] (ICP)'': similar to a CCP and with similar applications but the electrode consists of a coil wrapped around the chamber where plasma is formed.<ref>{{cite doi|10.1155/2010/164249}}</ref>
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| *''[[Wave heated plasma]]'': similar to CCP and ICP in that it is typically RF (or microwave). Examples include [[helicon discharge]] and [[electron cyclotron resonance]] (ECR).<ref>{{cite book|title=Plasma Chemistry|year=2008|publisher=Cambridge University Press|page=229|url=http://books.google.com/books?id=ZzmtGEHCC9MC&pg=PA229#v=onepage&q&f=false|isbn=9781139471732}}</ref>
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| ====Atmospheric pressure====
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| *''[[Arc discharge]]:'' this is a high power thermal discharge of very high temperature (~10,000 K). It can be generated using various power supplies. It is commonly used in [[Metallurgy|metallurgical]] processes. For example, it is used to smelt minerals containing Al<sub>2</sub>O<sub>3</sub> to produce [[aluminium]].
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| *''[[Corona discharge]]:'' this is a non-thermal discharge generated by the application of high voltage to sharp electrode tips. It is commonly used in [[ozone]] generators and particle precipitators.
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| *''[[Dielectric barrier discharge]] (DBD):'' this is a non-thermal discharge generated by the application of high voltages across small gaps wherein a non-conducting coating prevents the transition of the plasma discharge into an arc. It is often mislabeled 'Corona' discharge in industry and has similar application to corona discharges. It is also widely used in the web treatment of fabrics.<ref>{{cite doi|10.1163/156856106777657788}}</ref> The application of the discharge to synthetic fabrics and plastics functionalizes the surface and allows for paints, glues and similar materials to adhere.<ref>{{cite pmid|18930244}}</ref>
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| *''[[Capacitive discharge]]:'' this is a [[nonthermal plasma]] generated by the application of RF power (e.g., [[ISM band|13.56 MHz]]) to one powered electrode, with a grounded electrode held at a small separation distance on the order of 1 cm. Such discharges are commonly stabilized using a noble gas such as helium or argon.<ref>{{cite doi|10.1063/1.1323753}}</ref>
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| ==History==
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| Plasma was first identified in a [[Crookes tube]], and so described by [[Sir William Crookes]] in 1879 (he called it "radiant matter").<ref>Crookes presented a [[lecture]] to the [[British Association for the Advancement of Science]], in Sheffield, on Friday, 22 August 1879 [http://www.worldcatlibraries.org/wcpa/top3mset/5dcb9349d366f8ec.html] [http://www.tfcbooks.com/mall/more/315rm.htm]</ref> The nature of the Crookes tube "[[cathode ray]]" matter was subsequently identified by British physicist [[J. J. Thomson|Sir J.J. Thomson]] in 1897.<ref>Announced in his evening lecture to the [[Royal Institution]] on Friday, 30th April 1897, and published in {{cite journal|journal=[[Philosophical Magazine]]|volume=44|page=293|title=J. J. Thomson (1856-1940)|url=http://web.lemoyne.edu/~GIUNTA/thomson1897.html|year=1897}}</ref> The term "plasma" was coined by [[Irving Langmuir]] in 1928,<ref name="langmuir1928">{{cite doi|10.1073/pnas.14.8.627}}</ref> perhaps because the glowing discharge molds itself to the shape of the Crooks tube ([[Greek language|Gr.]] πλάσμα – a thing moulded or formed).<ref>{{cite book|author=Brown, Sanborn C.|chapter=Chapter 1: A Short History of Gaseous Electronics|editor=HIRSH, Merle N. e OSKAM, H. J.|title=Gaseous Electronics|volume=1|publisher=Academic Press|year=1978|isbn=978-0-12-349701-7}}</ref> Langmuir described his observations as:
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| <blockquote>Except near the electrodes, where there are ''sheaths'' containing very few electrons, the ionized gas contains ions and electrons in about equal numbers so that the resultant space charge is very small. We shall use the name ''plasma'' to describe this region containing balanced charges of ions and electrons.<ref name="langmuir1928" /></blockquote>
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| ==Fields of active research==
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| [[File:HallThruster 2.jpg|thumb|[[Hall effect thruster]]. The electric field in a plasma [[Double layer (plasma)|double layer]] is so effective at accelerating ions that electric fields are used in [[ion drive]]s.]]
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| <!--This list needs organization and pruning!-->
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| This is just a partial list of topics. See [[list of plasma (physics) articles]]. A more complete and organized list can be found on the web site Plasma science and technology.<ref>Web site for [http://www.plasmas.com/topics.htm Plasma science and technology]</ref>
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| <table><tr valign=top><td>
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| *Plasma theory
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| **[[Plasma equilibria and stability]]
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| **Plasma interactions with waves and beams
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| **[[Guiding center]]
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| **[[Adiabatic invariant]]
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| **[[Debye sheath]]
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| **[[Coulomb collision]]
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| *Plasmas in nature
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| **The Earth's [[ionosphere]]
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| **[[Aurora (astronomy)|Northern and southern (polar) lights]]
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| **Space plasmas, e.g. Earth's [[plasmasphere]] (an inner portion of the [[magnetosphere]] dense with plasma)
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| **[[Astrophysical plasma]]
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| **[[Interplanetary medium]]
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| *Industrial plasmas
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| **[[Plasma chemistry]]
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| **[[Plasma processing]]
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| **[[Plasma spray]]
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| **[[Plasma display]]
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| **[[Plasma source]]s
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| **[[Dusty plasma]]s
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| </td><td>
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| *[[Plasma diagnostics]]
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| **[[Thomson scattering]]
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| **[[Langmuir probe]]
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| **[[Spectroscopy]]
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| **[[Interferometry]]
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| **[[Ionospheric heater|Ionospheric heating]]
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| **[[Incoherent scatter]] radar
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| *Plasma applications
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| **[[Fusion power]]
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| ***[[Magnetic fusion energy]] (MFE) — [[tokamak]], [[stellarator]], [[reversed field pinch]], [[magnetic mirror]], [[dense plasma focus]]
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| ***[[Inertial fusion energy]] (IFE) (also Inertial confinement fusion — ICF)
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| ***[[Plasma-based weaponry]]
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| **[[Ion implantation]]
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| **[[Ion thruster]]
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| **[[MAGPIE]] (short for ''Mega Ampere Generator for Plasma Implosion Experiments'')
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| **[[Plasma ashing]]
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| **Food processing ([[nonthermal plasma]], aka "cold plasma")
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| **[[Plasma arc waste disposal]], convert waste into reusable material with plasma.
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| **[[Plasma acceleration]]
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| **[[Plasma medicine]] (e. g. Dentistry<ref name="tws44">{{cite news
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| | title = High-tech dentistry – "St Elmo's frier" – Using a plasma torch to clean your teeth
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| | publisher = The Economist print edition
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| | date = Jun 17, 2009
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| | url = http://www.economist.com/displaystory.cfm?story_id=13794903&fsrc=rss
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| | accessdate = 2009-09-07
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| }}</ref>)
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| **[[Plasma window]]
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| </table>
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| | |
| <gallery>
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| File:Wispy 'Plasma Dancer' on the limb of the Sun.ogv|Solar plasma
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| File:Plasma Spraying Process.jpg|Plasma spraying
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| </gallery>
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| | |
| ==See also==
| |
| {{portal|Physics}}
| |
| {{div col|colwidth=30em}}
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| *[[Plasma torch]]
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| *[[Ambipolar diffusion]]
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| *[[Hannes Alfvén Prize]]
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| *[[Plasma channel]]
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| *[[Plasma parameters]]
| |
| *[[Plasma nitriding]]
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| *[[Magnetohydrodynamics|Magnetohydrodynamics (MHD)]]
| |
| *[[Electric field screening]]
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| *[[List of plasma physicists]]
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| *[[List of plasma (physics) articles]]
| |
| *[[List of publications in physics#Plasma physics|Important publications in plasma physics]]
| |
| *[[IEEE Nuclear and Plasma Sciences Society]]
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| *[[Quark–gluon plasma|Quark-gluon plasma]]
| |
| *[[Nikola Tesla]]
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| *[[Total electron content]]
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| {{div col end}}
| |
| | |
| ==Notes==
| |
| <references group="Note" />
| |
| | |
| ==References==
| |
| {{reflist|colwidth=30em}}
| |
| | |
| ==External links==
| |
| {{Sister project links | wikt=plasma | commons=Category:Plasma physics | b=Wikijunior:The Elements/Plasma | q=no | s=Special:Search/Plasma physics | v=Plasma | d=Q10251 | n=Special:Search/Plasma physics}}
| |
| *[http://www.freebookcentre.net/Physics/Plasma-Physics-Books.html Free plasma physics books and notes]
| |
| *[http://fusedweb.pppl.gov/CPEP/Chart_Pages/5.Plasma4StateMatter.html Plasmas: the Fourth State of Matter]
| |
| *[http://www.plasmas.org/ Plasma Science and Technology]
| |
| *[http://plasma-gate.weizmann.ac.il/directories/plasma-on-the-internet/ Plasma on the Internet] – a list of plasma related links.
| |
| *Introduction to Plasma Physics: [http://farside.ph.utexas.edu/teaching/plasma/lectures/lectures.html Graduate course given by Richard Fitzpatrick]|[http://silas.psfc.mit.edu/introplasma/index.html M.I.T. Introduction by I.H.Hutchinson]
| |
| *[http://starfire.ne.uiuc.edu/ Plasma Material Interaction]
| |
| *[http://c3po.barnesos.net/homepage/lpl/grapeplasma/ How to make a glowing ball of plasma in your microwave with a grape]|[http://stewdio.org/plasma/ More (Video)]
| |
| *[http://video.google.com/videoplay?docid=6732382807079775486&hl=en How to make plasma in your microwave with only one match (video)]
| |
| *[http://comphys.narod.ru OpenPIC3D – 3D Hybrid Particle-In-Cell simulation of plasma dynamics]
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| *[http://plasma-gate.weizmann.ac.il/pf/ Plasma Formulary Interactive]
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| | |
| {{State of matter}}
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| {{Nuclear Technology}}
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| | |
| {{good article}}
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| | |
| [[Category:Astrophysics]]
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| [[Category:Concepts in physics]]
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| [[Category:Electrical conductors]]
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| [[Category:Phases of matter|*Plasma]]
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| [[Category:Plasma physics|*]]
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| | |
| {{Link GA|ar}}
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