|
| title=Theory and Modeling of Self-Organization and Propagation of Filamentary Plasma Arrays in Microwave Breakdown at Atmospheric Pressure|year=2010|journal=[[Physical Review Letters]]|volume=104|issue=1|page=015002|doi= 10.1103/PhysRevLett.104.015002|bibcode=2010PhRvL.104a5002B
}}</ref> <!--(Vaata ka [[pintš]])-->
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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=S. L. Chin|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>
-->
===Löögid ja kaksikkihid===
===Tolmune plasma ja teraline plasma===
[[Tolmune plasma]] (ingl. ''dusty plasma'') sisaldab endas pisikesi laetud (tavaliselt kosmoses leiduvaid) tolmukübemeid, mis käituvad nagu plasma. Suurematest osakestest koosnevat plasmat nimetatakse ''teraliseks plasmaks'' (ingl. ''grain plasma'').
==Mathematical descriptions==
[[File:Magnetic rope.png|thumb|256px|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>]]
{{main|Plasma modeling}}
To completely describe the state of a plasma, we would need to write down all the
particle locations and velocities and describe the electromagnetic field in the plasma region.
However, it is generally not practical or necessary to keep track of all the particles in a plasma.
Therefore, plasma physicists commonly use less detailed descriptions, of which
there are two main types:
===Fluid model===
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.
===Kinetic model===
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.
In magnetized plasmas, a [[gyrokinetics|gyrokinetic]] approach can substantially reduce the computational expense of a fully kinetic simulation.
==Artificial plasmas==
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:
*The type of power source used to generate the plasma—DC, RF and microwave
*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)
*The degree of ionization within the plasma—fully, partially, or weakly ionized
*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>)
*The electrode configuration used to generate the plasma
*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)
*The application
===Generation of artificial plasma===
[[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]]]]
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).
[[File:Simple representation of a discharge tube - plasma.png|Simple representation of a DC discharge tube.]]
[[File:Cascade process of ionization.png|thumb|Cascade process of ionization. Electrons are ‘e−’, neutral atoms ‘o’, and cations ‘+’.]]
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=0306413329}}</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]]). This is a stage of avalanching ionization, 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).
With ample current density and ionization, this forms a luminous [[electric arc]] (essentially [[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}}</ref>|group="nb"}} [[Electrical resistance]] along the continuous electric arc creates [[heat]], which ionizes more gas molecules (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="nb"}} 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="nb">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>
===Examples of industrial/commercial plasma===
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 journal |doi=10.1016/j.jhazmat.2008.04.017 |author=Gomez, E., Rani, D.A., Cheeseman, C.R., Deegan, D., Wise, M., Boccaccini, A.R. |year=2009 |title=Thermal plasma technology for the treatment of wastes: A critical review |journal=Journal of Hazardous Materials |volume=161 |issue=2–3 |pages=614–626 |pmid=18499345}}</ref> surface treatments such as [[thermal 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= 0309045975}}</ref> metal cutting<ref name="Nemchinsky">{{cite journal |doi=10.1088/0022-3727/39/22/R01 |author=Nemchinsky, V.A., Severance, W.S. |year=2006 |title=What we know and what we do not know about plasma arc cutting |journal=J. Phys. D: Appl. Phys. |volume=39 |issue=22 |pages=R423–R438 |bibcode = 2006JPhD...39R.423N}}</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=3527406735}}</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>
====Low-pressure discharges====
*''[[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=Dr. David P. Stern |accessdate=2010-05-19}}</ref>
*''[[Capacitively coupled plasma]] (CCP)'': similar to glow discharge plasmas, but generated with high frequency RF electric fields, typically 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=J. Vac. Sci. Technol. B |volume=16 |issue=1 |pages=173–182 |url=http://physics.nist.gov/MajResProj/rfcell/Publications/MAS_JVSTB16_1.pdf}}</ref>
*''[[Inductively coupled plasma]] (ICP)'': similar to a CCP and with similar applications but the electrode consists of a coil wrapped around the discharge volume that inductively excites the plasma.{{Citation needed|date=August 2008}}
*''[[Wave heated plasma]]'': similar to CCP and ICP in that it is typically RF (or microwave), but is heated by both electrostatic and electromagnetic means. Examples are [[helicon discharge]], [[electron cyclotron resonance]] (ECR), and [[ion cyclotron resonance]] (ICR). These typically require a coaxial magnetic field for wave propagation.{{Citation needed|date=August 2008}}
====Atmospheric pressure====
*''[[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 melt rocks containing Al<sub>2</sub>O<sub>3</sub> to produce [[aluminium]].
*''[[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.
*''[[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 journal|author=F. Leroux et al. |title=Atmospheric air plasma treatments of polyester textile structures|journal=Journal of Adhesion Science and Technology|volume=20|issue=9|pages=939–957|year=2006|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 journal|author=F. Leroux et al.|doi=10.1016/j.jcis.2008.09.062|title=Polypropylene film chemical and physical modifications by dielectric barrier discharge plasma treatment at atmospheric pressure|year=2008|journal=Journal of Colloid and Interface Science|volume=328|page=412|pmid=18930244|issue=2}}</ref>
*''[[Capacitive discharge]]:'' this is a [[nonthermal plasma]] generated by the application of RF power (e.g., 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 journal|author=J. Park et al.|doi=10.1063/1.1323753|title=Discharge phenomena of an atmospheric pressure radio-frequency capacitive plasma source|year=2001|journal=Journal of Applied Physics|volume=89|issue=1|page=20|bibcode = 2001JAP....89...20P}}</ref>
==History==
Sõna '''plasma''' tuleneb kreekakeelsest sõnast ''plásma'', verb ''plássein'', mis tähendab "vormima" või "kujutama".<ref>http://dictionary.reference.com/browse/plasma</ref> Termini '''plasma''' võttis esmakordselt kasutusele [[Irving Langmuir]] 1928, sest tema loodud mitmekomponendiline kõrgelt ioniseeritud gaas meenutas talle [[vereplasma]]t.<ref name="Fridman" />
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|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 journal|author=I. Langmuir|doi=10.1073/pnas.14.8.627|title=Oscillations in ionized gases|journal=Proc. Nat. Acad. Sci. U.S.|volume=14|issue=8|page=628|year=1928|bibcode = 1928PNAS...14..627L}}</ref> perhaps because the glowing discharge molds itself to the shape of the Crooks tube ([[Greek language|Gr.]] πλάσμα – "to mold").<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|local=Nova Yorque|publisher=Academic Press|year=1978|ISBN=0-12-349701-9}}</ref> Langmuir described his observations as:
<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>
==Fields of active research==
[[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.]]
<!--This list needs organization and pruning!-->
This is just a partial list of topics. 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>
<table><tr valign=top><td>
*Plasma theory
**[[Plasma equilibria and stability]]
**Plasma interactions with waves and beams
**[[Guiding center]]
**[[Adiabatic invariant]]
**[[Debye sheath]]
**[[Coulomb collision]]
*Plasmas in nature
**The Earth's [[ionosphere]]
**[[Aurora (astronomy)|Northern and southern (polar) lights]]
**Space plasmas, e.g. Earth's [[plasmasphere]] (an inner portion of the [[magnetosphere]] dense with plasma)
**[[Astrophysical plasma]], [[Interplanetary medium]]
*Industrial plasmas
**[[Plasma chemistry]]
**[[Plasma processing]]
**[[Plasma spray]]
**[[Plasma display]]
</td><td>
*[[Plasma source]]s
*[[Dusty plasma]]s
*[[Plasma diagnostics]]
**[[Thomson scattering]]
**[[Langmuir probe]]
**[[Spectroscopy]]
**[[Interferometry]]
**[[Ionospheric heater|Ionospheric heating]]
**[[Incoherent scatter]] radar
*Plasma applications
**[[Fusion power]]
***[[Magnetic fusion energy]] (MFE) — [[tokamak]], [[stellarator]], [[reversed field pinch]], [[magnetic mirror]], [[dense plasma focus]]
***[[Inertial fusion energy]] (IFE) (also Inertial confinement fusion — ICF)
***[[Plasma-based weaponry]]
**[[Ion implantation]]
**[[Ion thruster]]
**[[MAGPIE]] (short for ''Mega Ampere Generator for Plasma Implosion Experiments'')
**[[Plasma ashing]]
**Food processing ([[nonthermal plasma]], aka "cold plasma")
**[[Plasma arc waste disposal]], convert waste into reusable material with plasma.
**[[Plasma acceleration]]
**[[Plasma medicine]] (e. g. Dentistry <ref name=tws44>{{cite news
| author =
| title = High-tech dentistry – "St Elmo's frier" – Using a plasma torch to clean your teeth
| publisher = The Economist print edition
| date = Jun 17th 2009
| url = http://www.economist.com/displaystory.cfm?story_id=13794903&fsrc=rss
| accessdate = 2009-09-07
}}</ref>)
**[[Plasma window]]
</table>
==Vaata ka==
| 