Stroth_Transport in Toroidal Plasmas.pdf

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1、9TransportinToroidalPlasmasU.StrothInstitutf¨urExperimentelleundAngewandtePhysik,Christian-Albrechts-Univ.zuKiel,Olshausenstr.40,24098Kiel,Germanystroth@physik.uni-kiel.deAbstract.Tounderstandthemechanismsdeterminingconfinementofenergyandparticlesintoroidalplasmas,isoneofthemostpro

2、minentandambiguousobjec-tivesoffusionresearch.Thereisawidespectrumofdifferentphysicalprocessesinvolvedinplasmatransport,rangingfromthecomplexityofparticletrajectoriesinthree-dimensionalmagneticconfigurationsoverkineticeffectsrelatedtothepar-ticledistributionfunctionstothewidefieldofpl

3、asmaturbulence.Thischapteraimstogiveanoverviewandanintuitiveunderstandingofthevariousapproaches.Thestartingpointofthischapterisaplasmaconfinedinatoroidalmagneticfieldasproducedbytokamakorstellaratorexperiments(seealsoChap.7inPartII).Theplasmapressureisassumedtobelowenoughinordertogu

4、ar-anteeMHDstability(seeChap.4inPartI).Hencethezeroth-orderplasmaflowisdirectedtangentiallytothemagneticfluxsurfacesandtheradialcom-ponentofitvanishes.Suchaplasmaisneverthelessnotperfectlyconfined.Inordertomaintainconstantplasmaconditions,continuousheatingandpar-ticlerefuellingofthep

5、lasmaisrequired.Ifrefuellingandheatingcease,theplasmatemperatureanddensitydecayexponentially.Thecharacteristictimeconstantsofthedecayaretheparticleandenergyconfinementtimes.Particleandenergylossesarecausedbytransportduetotwodifferenttypesofprocesses,whichbothgobeyondthephysicsofline

6、aridealMHD.Resistivityorcollisionsbetweenparticlesinthepresenceofgradientsinthethermodynamicvariablesleadtodistortionsinthedistributionfunctions.Thiscausescollisionaltransportwhichisthebasicleveloftransportalwayspresentinaplasma.Inmanycases,collisionaltransportisonlyofminorimporta

7、nceforparticleandenergyconfinement.Sinceitneedsnottobeambipolar,however,itdeterminestheplasmapotentialandtheradialelectricfield.Thesecondandforconfinementtimesmoreimportantcomponentistheturbulentorsocalledanomaloustransport.AnintroductiontoturbulenceisgiveninChap.8inPartII.Itisdriven

8、byfluctuationsintheplasmaparameter