等离子体基本知识

第一章等离子体内容基本概念气体分子运动理论等离子体参数等离子体形成方法1.基本概念1.1物质的几种基本状态Solids:MattersconsistingofmoleculesandatomswithveryhighlevelsofarrangementMobilityofatomsandmoleculesisverylimited.Liquids:Mattersconsistingofatomsormoleculeswithclosedarrangements,TheremayexistcrystallinearrangementsofparticlesinsmallcomplexeswithinarangeofnmCharacterizedwitheasinessofmobility.Gases:Systemsofatomsormoleculesbehavingasfreeentities.Themattersinthegaseousphaseatthenormalconditionsarecalledgases.Othermatterspassingintothegaseousphasebyincreasingtemperatureorpressuredroparecalledvapors.Plasma:Aphysicalsystemconsistingofneutrals,molecules,atoms,excitedparticles,ions,electronsandelectromagneticradiation.等离子体是物质第四态固体冰液体水气体水汽等离子体电离气体温度00C1000C100000C电离气体是一种常见的等离子体放电是使气体转变成等离子体的一种常见形式等离子体电离气体普通气体等离子体放电1.2粒子的种类Moleculethesmallestunitofmatterthatcanexistbyitselfandretainallitschemicalproperties.Inamoleculeagroupofatomsareheldtogetherbychemicalforces.AtompreviouslyunderstoodasindivisiblepieceofmatterfirstpostulatedbytheGreeks,butknowntobecomposedofnucleuscircledbyelectrons.Nucleusaheavypositivelychargedcenteroftheatom,composedofprotonsandneutrons.Morethan100typesofnuclearparticlehavebeendiscovereduptonow.Electronasmallnegativelychargedparticlethatnormallycirclesthenucleusofanatom.Protonmassivepositivelychargedparticlethatisthenucleusofthehydrogenatom.Neutronaparticleofapproximatelythesamemassasproton,butuncharged.Outsidethenucleusaneutroncannotexistalone;Itisunstableandwilldecayintoprotonandanelectron.Ionanatomormoleculethatbylossorgainofoneormoreelectronshasacquiredanetcharge.Lossofelectronsresultsinapositiveion,gainofelectronresultsinanegativeion.2.气体分子运动理论2.1MaxwelliandistributionRandomvelocityofelectronorgasmoleculesisdescribedbyMaxwelliandistributionwhenthesystemisatthermalequilibrium.2.2DefinitionofVelocities:Mostprobablevelocity(最可几速率）Averagevelocity:Rootmeansquare(rms)velocity(均方根速率）KineticenergyofamolecularGasH2HeH2ON2O2ArCOCO2HgVelocity(m/s)16931208565454425380454362170Meanvelocitiesofsomegasat16℃231VmnPn——thenumberdensityv——rootmeansquarevelocityofthemolecularm——molecularmassMixture:P=P1+P2+P3+P4+……2.3PressureDefinition:Effectofcollisionsbetweenthemolecularandthewall2.4Meanfreepath(平均自由程）SchematicofthemotionofthemolecularPdkT22)(1053cmPT=25℃Molecular:Ion:2i24eElectron:BecauseoflargespeedBecauseoflargespeedandsmalldiameterMeanfreepathatdifferentpressuresThisarrivalrateR,orFluxF,RorF=nv/4Themoleculardensityn,n=p/kTThemeanspeedofthemolecules，v=(8kT/m)1/22.5ArrivalrateofatomsataSurface2.6Themonolayerarrivaltime，IfN0isthenumberofatomsinamonolayer(theMLunit)thenR=N0DegreeofVacuumPressure(Torr)GasDensity,ρ(moleculesm-3)MeanFreePath(m)Time/ML,tML(s)Atmospheric7602x10257x10-810-9Low13x10225x10-510-6Medium10-33x10195x10-210-3High10-63x1016501UltraHigh10-103x10125x105104CollisionFreeConditions:P~10-6TorrMaintainaCleanSurface:P~10-10Torr3.等离子体Collision：ReactionCrossSection3.1等离子体形成过程ExcitationandIonizationExcitationandionizationbyanelectronimpact：Excitationandionizationbyanioncollision：Excitationandionizationbyaneutralparticlecollision：Excitationandionizationbyradiation：RecombinationIon-ElectronRecombination：A++eA*+hvIon–IonRecombination：A++B-AB+hvAttachmentanddetachment：M(g)+eM-(g)3.2.1Themeankineticenergy32122kTmvrsvrsisrootmeansquarevelocitym-massoftheparticleT-absolutetemperaturekisBoltzmannconstant.3.2等离子体参数3.2.2TemperatureofplasmaTheelectrontemperatureTe,TheiontemperatureTi,ThegastemperatureTg.3.2.3PlasmaDensityPlasmaisacollectionofparticlesconsistingofelectrons,ionsandexcitedparticlesElectrondensityofne,isknownastheplasmadensity.nnnnnnnininie121......在等离子体中引入带负电荷的薄层，经过一定的时间……..德拜(Debye)屏蔽3.2.4Debyelength－在等离子体中引入带负电荷的薄层，经过一定的时间，等离子体中的电子、离子将移动，屏蔽电场——德拜屏蔽德拜(Debye)屏蔽－屏蔽层厚度：德拜长度D特征响应时间：p＝D/vT＝1/wp2/10DeenTe当Te=4V和ne=1010cm-3时，德拜长度=0.14mm在等离子体内部，正、负电荷数几乎相等——准中性neni3.2.5准电中性3.2.6等离子体振荡在无外加驱动场的条件下，一个平板形等离子体会发生振荡2/1002mnepewxeeEdtdm2200exenE密度(cm-3)温度(度)太阳核心磁约束聚变霓虹灯北极光火焰闪电日冕氢弹星际空间荧光气体液体固体人类居住环境惯性聚变星云太阳风3.2.7等离子体参数空间宇宙中90％物质处于等离子体态地球上，人造的等离子体也越来越多地出现在我们的周围。•日常生活中：日光灯、电弧、等离子体显示屏、臭氧发生器•典型的工业应用：等离子体刻蚀、镀膜、表面改性、喷涂、烧结、冶炼、加热、有害物处理•高技术应用：托卡马克、惯性约束聚变、氢弹、高功率微波器件、离子源、强流束、飞行器鞘套与尾迹3.2.8等离子体分类冷等离子体Te≠Ti,Ta热等离子体Te＝Ti,Ta电弧、碘钨灯极光、日光灯电子温度100000C1eV聚变、太阳核心高温等离子体低温等离子体3.2.9低温等离子体的分类Coldplasma：plasmainastateofthermalnon-equilibriumiscalledcoldplasmaThelackofthermalequilibriumbetweentheelectrontemperatureandgastemperature.TheelectrontemperatureTemaybeafewtenthousandsKwhilethegastemperaturecanachievearound1000K.Generatedbyadirectcurrent(dc)glowdischarge.ahighfrequencyormicrowavedischargeatlowpressure.ThermalPlasma:TheplasmaisinthermalequilibriumTheenergydistributionsofelectrons(characterizedbyTe)andgasmolecules(characterizedbyTg)arenearlythesameGeneratedbyarcdischarge3.3等离子体基本条件空间尺度要求：等离子体尺度远大于德拜长度DL时间尺度要求：等离子体碰撞时间、存在时间远大于特征响应时间p集合体要求：在德拜球中粒子数足够多，具有统计意义ND＝ne(4D3/3)14.低温冷等离子体形成方法真空条件下直流辉光放电真空条件下的射频辉光放电真空条件下的微波等离子体电晕放电大气等离子体炬大气条件下的介质层放电4.1放电特性曲线pd(cm.Torr)0.11101001