Plasma: erinevus redaktsioonide vahel
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{{Koolitöö|14. novembril 2011|kool=TÜ loodus- ja tehnoloogiateaduskond}}
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:''Sõna teiste tähenduste kohta vaata [[Plasma (täpsustus)]].''
[[File:Plasma-lamp 2.jpg|thumb|right| [[Plasmakera]] on illustratsiooniks mõnedele keerulisematele plasmanähtustele, nagu filamentatsioon<!--[[Current filament|filamentation]]-->. Nähtav [[kiirgus]] on põhjustatud neutraalsete [[aatom]]ite ja [[ioon]]ide põrkumisel [[elektron]]idega tekkinud ergastuste relaksatsioonist. Neis protsessides kiiratava valguse [[spekter]] on igal aatomil ja ioonil spetsiifiline ning selle spektri mõõtmine võimaldab kindlaks määrata, millistest [[Keemiline_element|elementidest]] plasma koosneb.]]
[[Füüsika]]s ja [[keemia]]s tähendab '''plasma''' [[agregaatolek]]ut, mis sarnaneb [[gaas]]ile, kuid kus teatud hulk osakesi on [[ionisatsioon|ioniseeritud]]. Ionisatsiooni toimumiseks on osakesele vaja anda [[energia]]hulk, mis on suurem antud osakese [[ionisatsioonienergia]]st. Ioniseerimata gaasi ja kergelt ioniseeritud gaasi käitumise määravad valdavalt gaasi osakeste binaarsed (kahe osakese vahelised) põrked. Kui gaasi [[ionisatsiooniaste]] on piisavalt kõrge, hakkavad selle käitumist olulisel määral mõjutama [[elektrodünaamika|elektrodünaamilised]] ja [[magnethüdrodünaamika|magnethüdrodünaamilised]] efektid. Teatud piirist loetakse sellist aine olekut plasmaks.
Plasmal leidub [[tahkis]]te, [[vedelik]]e ja [[gaas]]idega võrreldes võrdlemisi erinevaid omadusi, mistõttu loetakse teda eraldiseisvaks [[agregaatolek]]uks (aine neljandaks olekuks). Erinevalt gaasilisest olekust võib plasma [[magnetväli|magnetvälja]] olemasolul moodustada struktuure, nagu näiteks [[filament|filamendid]], joad ja [[topeltkiht|topeltkihid]]. Plasma on [[universum]]is [[barüonaine|tavaaine]] kõige levinumaks agregaatolekuks, millest enamik eksisteerib hõreda [[galaktikatevaheline keskkond|galaktikatevahelise plasmana]] <!--(particularly [[intracluster medium]])--> ja tähtedes.
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===Plasma definitsioon===
Sageli defineeritakse plasmat kui ioniseeritud gaasi, mis on peaaegu elektriliselt neutraalne (laeng on võrdne nulliga või väga väike) ja mis koosneb märkimisväärsel hulgal elektriliselt laetud osakestest, mis on suutelised muutma kogu süsteemi elektrilisi omadusi ja käitumist.<ref name="Fridman">{{cite book|author=A. Fridman|title=Plasma Chemistry|url=http://books.google.com/books?id=ZzmtGEHCC9MC|publisher=Cambridge University Press|year=2008|isbn=0521847353}}</ref>
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" /> Mitterangelt kirjeldatakse plasmat kui keskkonda, mis koosneb positiivselt ([[ioon]]id) ja negatiivselt ([[elektron]]id) laetud osakestest, millede summaarne laeng on ligikaudu võrdne nulliga. On oluline ära märkida, et need osakesed </ref> Plasmat defineeritakse ka järgnevate kriteeriumite abil (kui aine olek vastab nendele kriteeriumitele, on tegemist plasmaga):<ref name="Hazeltine">{{cite book|author=R. O. Dendy|title=Plasma Dynamics|url=http://books.google.com/?id=S1C6-4OBOeYC|publisher=Oxford University Press|year=1990|isbn=0198520417}}</ref><ref>{{cite book|author=Daniel Hastings, Henry Garrett|title=Spacecraft-Environment Interactions|isbn=0521471281|publisher=Cambridge University Press|year=2000}}</ref>
#'''Plasmalähendus''': Laetud osakesed peavad olema teineteisele küllalt
#'''Põhiosa interaktsioonid''': Debye varjestuse kaugus (defineeritud ülal) on plasma
#'''Plasmasagedus''': Elektronide
===Plasma füüsikaliste parameetrite ulatus===
Plasma parameetrid võivad omada väärtusi mitmete suurusjärkude ulatuses, kuid vaatamata sellele on suurusjärkudes erinevate parameetritega plasmade käitumine sarnane.<!--(see [[plasma scaling]])-->. Järgnev tabel käsitleb klassikalisi atomaarseid plasmasid ning jätab välja eksootilisemad kvantplasmad, nagu [[kvark-gluuon plasma]]d:
[[File:Plasma scaling.svg|thumb|250px|'''Plasmade ulatused'''. Elektronide kontsentratsioon kasvab vertikaalsuunas alt üles, temperatuur kasvab horisontaalsuunas vasakult paremale. Vabu elektrone metallis võib lugeda elektronplasmaks.<ref>{{cite journal|author=Peratt, A. L.|bibcode=1996Ap&SS.242...93P |title=Advances in Numerical Modeling of Astrophysical and Space Plasmas|year=1966|journal=Astrophysics and Space Science|volume=242|issue=1–2|pages=93–163|doi=10.1007/BF00645112}}</ref>]]
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===Ionisatsiooniaste===
===Temperatuurid===
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Plasma temperatuuri mõõdetakse enamasti [[kelvin]]ites või [[elektronvolt]]ides ning on – mitteformaalselt – soojusliku kineetilise energia mõõduks osakese kohta. Ionisatsiooni alal hoidmiseks on tavaliselt vaja väga kõrgeid temperatuure, mis on üheks plasmat eristavaks omaduseks. Plasma ionisatsiooniaste on määratud "elektrontemperatuuri" ja [[ionisatsioonienergia]] suhtega (ning nõrgemalt tihedusega). Seda seost nimetatakse [[Saha võrrand]]iks. Madalatel temperatuuridel kipuvad ioonid ja elektronid rekombineeruma aatomiteks<ref name="Nicholson">{{cite book |title=Introduction to Plasma Theory |last=Nicholson |first= Dwight R. |year=1983 |publisher=John Wiley & Sons |isbn=047109045X}}</ref> ja plasma muutub pikapeale gaasiks.
Enamikel juhtudel on elektronid küllalt ligidal [[soojuslik tasakaal|soojuslikule tasakaalule]], nii et nende temperatuur on küllalt hästi defineeritud, isegi kui eksisteerib oluline kõrvalekalle [[Maxwell–Boltzmanni jaotus|Maxwelli]] energia [[jaotusfunktsioon]]ist,
Sõltuvalt elektronide, ioonide ja neutraalsete osakeste tempuuride
Plasmat nimetatakse mõnikord "kuumaks", kui ta on peaaegu täielikult ioniseeritud, või "külmaks", kui vaid väike murdosa (näiteks 1%) gaasi molekulidest on ioniseeritud, kuid leidub ka teisi levinud definitsioone. Isegi "külmas" plasmas on elektronide temperatuur siiski mitu tuhat Celsiuse kraadi. Tehnilistes rakendustes kasutatavad plasmad on tavaliselt "külmad" eelmainitud tähenduses.
===Potentsiaalid===
[[File:Lightning over Oradea Romania 3.jpg|thumb|300px|right|[[Lightning]]
is an example of plasma present at Earth's surface.
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>.]]
Since plasmas are very good conductors, electric potentials play an important role.
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.
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]]":
:<math>n_e \propto e^{e\Phi/k_BT_e}</math>.
Differentiating this relation provides a means to calculate the electric field from the density:
:<math>\vec{E} = (k_BT_e/e)(\nabla n_e/n_e)</math>.
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]].
In [[
===
===Comparison of plasma and gas phases===
Plasma is often called the ''fourth state of matter''. It is distinct from other lower-energy [[states of matter]]; most commonly [[solid]], [[liquid]], and [[gas]]. 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:
{| class="wikitable"
|-
!
|-
! [[Electrical resistivity and conductivity|Electrical conductivity]]
| '''
| '''Usually very high''': For many purposes, the conductivity of a plasma may be treated as infinite.
|-
! Independently acting species
| '''One''': All gas particles behave in a similar way, influenced by [[gravity]] and by [[collision]]s with one another.
| '''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]].
|-
! Velocity distribution
| '''[[Maxwell–Boltzmann distribution|Maxwellian]]''': Collisions usually lead to a Maxwellian velocity distribution of all gas particles, with very few relatively fast particles.
| '''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.
|-
! Interactions
| '''Binary''': Two-particle collisions are the rule, three-body collisions extremely rare.
| '''Collective''': Waves, or organized motion of plasma, are very important because the particles can interact at long ranges through the electric and magnetic forces.
|}
==Levinud plasmad==
[[File:ISS Crew Views STS-135 Landing.jpg|thumb|right|[[Kosmosesüstik Atlantis|Kosmosesüstik ''Atlantis'']]e poolt [[Maa atmosfäär]]i taassisenemisel jäetud plasmajälg, nagu seda võis näha [[rahvusvaheline kosmosejaam|rahvusvahelisest kosmosejaamast]] (ISS).]]
<!--{{see|Astrophysical plasma|Interstellar medium|Intergalactic space}}-->
Plasma on vaieldamatult kõige levinum [[agregaatolek]] universumis, nii massi kui ka ruumala poolest.<ref>
{| class="wikitable"
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==Complex plasma phenomena==
[[File:Main tycho remnant full.jpg|right|right|thumb|300px|The [[Supernova remnant|remnant]] of "[[SN 1572|Tycho's Supernova]]", a huge ball of expanding plasma. The outer shell shown in blue is X-ray emission by high-speed electrons.]]
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:
===Filamentation===
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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=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="
===Examples of industrial/commercial plasma===
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==History==
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:
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</table>
==
{{portal|Physics}}
{{Commons category|Plasma physics}}
*[[Ambipolar diffusion]]
*[[Hannes Alfvén Prize]]
*[[Plasma channel]]
*[[Plasma parameters]]
*[[Plasma nitriding]]
*[[Magnetohydrodynamics|Magnetohydrodynamics (MHD)]]
*[[Electric field screening]]
*[[List of plasma physicists]]
*[[list of publications in physics#Plasma physics|Important publications in plasma physics]]
*[[IEEE Nuclear and Plasma Sciences Society]]
*[[Quark–gluon plasma|Quark-gluon plasma]]
*[[Nikola Tesla]]
==Märkused==
<references group="
==Viited==
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