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1、Thecollisionlessnatureofhigh-temperatureplasmasT.M.O’NeilDepartmentofPhysics,UniversityofCaliforniaatSanDiego,LaJolla,California92093F.V.CoronitiDepartmentofPhysicsandAstronomy,UniversityofCalifornia,LosAngeles,LosAngeles,California90024Twophenomenathatillustratethecollisionlessnat
2、ureofhightemperatureplasmasareLandaudamping(or,moregenerally,theresonantwave-particleinteraction)andcollisionlessshockwaves.The®rsthalfofthispapertracesLandau'sideathroughtheyearsasitistestedexperimentally,extendednonlinearly,andapplied.Thesecondhalftracestheprogressinunderstanding
3、collisionlessshocksinspaceandastrophysicalplasmas.[S0034-6861(99)03002-0]I.INTRODUCTIONpv2]fp0g~k!5v~k!2U,(1)Animportantpropertythatdistinguisheshightem-2k]vzv~k!/kperatureplasmasfromnormal¯uids,evenfromcon-wherev(k)isthemodefrequencyandvpducting¯uidssuchasliquidmetals,isthatthepla
4、smas21/25(4pne/m),istheelectronplasmafrequency.Here,aretoa®rstapproximationcollisionless.Inalaboratoryeandmaretheelectronchargeandmassandnistheplasma,themean-free-pathbetweencollisionscanbedensity.Thefunctionf0(vz)5*dvxdvyF0(vx,vy,vz)ismuchlargerthanthedimensionsoftheplasma.Inspace
5、thedistributionofelectronvelocitiesparalleltothedi-andastrophysicalplasmas,themean-free-pathcaneasilyrectionofpropagation,whereF0(vx,vy,vz)isthedistri-exceedthedimensionsofthestructuresofinterest.Thebutionoverallthreevelocitycomponents.Thesubscriptcollisionlessnaturenecessitatesaki
6、netictreatmentandzeroindicatesthatthedistributionreferstotheunper-introducesavarietyofsubtlenewphenomena.Forex-turbedequilibriumstate,whichisassumedtobespa-ample,Landaudamping(orgrowth)resultsfromthetiallyhomogeneous.Langmuirwavesarespecialinthatresonantinteractionofawavewithfreest
7、reamingpar-theelectronsdominatethedynamics;moregenerally,ticles,aresonancethatwouldbespoiledbycollisionsinbothelectronsandionscontributetog(k).Clearly,theanormal¯uid.Also,thecollisionlessnaturechallengesdamping(orgrowth)isassociatedwithelectronsthatusto®ndnewdescriptionsforfamiliar
8、phenomena.Forsatisfytherel
