在tcv托卡马克中用中性束加热的一般性研究外文翻译.docx

在tcv托卡马克中用中性束加热的一般性研究外文翻译.docx

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在tcv托卡马克中用中性束加热的一般性研究外文翻译

英文原文

AscopingstudyoftheapplicationofneutralbeamheatingontheTCVtokamak

AlexanderN.Karpushova,∗,BasilP.Duvala,RenéChavana,EmilianoFableb,Jean-MichelMayora,OlivierSautera,HenriWeisena

aEcolePolytechniqueFédéraledeLausanne（EPFL）,CentredeRecherchesenPhysiquedesPlasmas,AssociationEuratom-ConfédérationSuisse,

CH-1015Lausanne,Switzerland

bMax-Planck-InstitutfürPlasmaphysik,Euratom-IPPAssociation,Boltzmannstra遝2,D-85748Garching,Germany

Articleinfo

Articlehistory:

Availableonline17March2011

Keywords:

TCVtokamakNeutralbeamheating

Abstract

TheTCVtokamakcontributestothephysicsunderstandingoffusionplasmas,broadeningtheparameterrangeofreactorrelevantregimes,byinvestigationsbasedonanextensiveuseoftheexistingmainexperimentaltools:

flexibleshapingandhighpowerrealtime-controllableelectroncyclotronheating（ECH）andcurrentdrive（ECCD）systems.AproposedimplementationofdirectionheatingontheTCVbytheinstallationofaneutralbeaminjection（NBI）withatotalpowerofwouldpermitanextensionoftheaccessiblerangeofiontoelectrontemperatures（）towellbeyondunity,dependingontheNBI/ECHmixandtheplasmadensity.ANBIsystemwouldprovideTCVwithatoolforplasmastudyatreactorrelevantratios∼1andininvestigatingfastionandMHDphysicstogetherwiththeeffectsofplasmarotationandhighplasmaˇscenarios.ThefeasibilitystudiesforaNBIheatingonTCVpresentedinthispaperwereundertakentoconstructaspecificationfortheneutralbeaminjectorstogetherwithanexperimentalgeometryforpossibleoperationalscenarios.

1.Introduction

TCVisacompact（majorradius,minorradius,toroidalmagneticfield,plasmacurrentof）,highelongated（vesselelongation3）toroidalfusionexperimentalmachine.Highpower,real-timecontrollable,injectionofwavesatthesecond（X2,3MW）andthird（X3,1.5MW）harmonicsofelectroncyclotronfrequencyconstitutetheprimarymethodofheating（ECH）anddrivingnon-inductivecurrent（ECCD）intheplasmawithelectrondensities,electrontemperatures,iontemperatures.TheflexibleplasmashapingandpowerfulECHsystemareusedtocontributeinmanyareasoftokamakresearch[1].

HighpowerX2-ECH,forrelativelylowdensityTCVplasmas，doesnotallowoperationatreactorrelevantratiosofiontoelectrontemperatures,astheelectron-ionclassicalCoulombcollisionthermalequilibrationtimeissignificantlylongerthanthecharacteristicconfinementtimes.ImplementationofdirectionheatingattheMWpowerlevelwouldallowtheextensionoftobeyondunityandfillthegapbetweenpresentpredominantlyelectronheatedexperimentsandfusionreactor[2].Theiontoelectrontemperatureratioisofparticularinterestintheprojectionofthetransportmechanismsfromexistingexperimentstoburningplasma.Theratioplaysakeyroleinthetransitionbetweeniontemperaturegradient（ITG）andtrappedelectron（TEM）modedominatedturbulentenergytransportmechanisms.IncreasingreducestheionandelectronenergytransportasobservedinDIII-DH-modeexperiments[3].NBIheatingmaythereforeallowTCVplasmastoreachhigherˇvalues,closetotheideallimitorbeyondathighelongation.

Injectionoffastatombeams（NBI）intotokamakisapossibleandwellusedmethodofauxiliaryheating.Followingionizationandcharge-exchange,fastatomsofthebeamaretrappedasplasmaionsandtransportenergyandmomentummainlytobulkionsifthefastionenergyisbelowcriticalenergy（Ecrit∼20forhydrogenbeamanddeuteriumplasma,）[4].TheproposedNBIsystemwouldthusalsoprovideTCVwithatooltoinvestigatefastionandrelatedMHDphysics[5]aswellasplasmarotationcontrol[6]forwhichTCVisalreadywelldiagnosed.ThebehaviouroftoroidalrotationinthevicinityofanITBisofparticularinterestbecauseofitsinfluenceontriggeringand/orsustainingthebarrier.TargetplasmascouldincludeITER-likeH-modeshapestogetherwithadvancedshapes,recentlyaccessibleonlyinohmicregimes【7】。

2.ScenariosofNBIheatingexperiments

ExperimentalscenariosfortheNBIexperimentsontheTCVarestronglylinkedtolimitationsimposedbyECHandECCD.FortheeITBsandfullynon-inductivescenariosonTCV,theaccessibleplasmadensityislimitedbytheX2cut-offincurrentdriveandelectronheatingexperiments.Conversely,efficientX3depositionisobtainedforelectrondensityintherangeofand

TheASTRAcode[8]wasusedtosimulatetheplasmaresponsetoneutralbeamheatinginthegeometryoftheTCVtokamak.ThecodesolvesequationsforelectronandiontemperatureandplasmacurrentdensitywiththeprescribedelectrondensityprofileandtotalplasmacurrenttakenfromTCVexperiment.Theuseoftheneoclassicalionheatconductivity[9]givesthatismatchedtotheCXRS[10]measurement.Theexperimentalelectronheatconductivitywasnormalisedtoobtaintheenergyconfinementtimepredictedbypowerlawscalings[11]:

IPB98（y,2）forELMyH-modeandstandardpowerlawregressionforL-mode.TheECpowerdepositionprofilewascalculatedbytheTORAYray-tracingcode.

2.1.HighdensityELMyH-moderegime

ThetargetparametersformodellingweretakenfromOhmicandX3heated（Table1,No.1.0）stationaryELMyH-modephasesofTCVdischarge[12].About95%ofinjecteddeuteriumNBpowercanbeabsorbedbytheplasmafortangentiallyinjectedbeam.Thesimulationsshowthatcanbeachievedwith∼0.8MWofNBIand1.3MWX3-ECH（Figs.1and2）.Accesstoshouldbeattainableatincreased（）NBorreducedX2-ECHpower.Thefastioncharge-exchange（CX）lossesonbackgroundneutralsstronglydependonthefirstwallrecyclingconditions,thedensityofbackgroundatoms,obtainedfromEIRENEmodelling,reducestheNBheatingefficiencyby∼15%（No.1.4）,CXlossesonbeamneutralsareneglectable.

Athighplasmadensityandcurrent,neutralbeaminjectioncouldresultinanincreaseofthethermalfrom2.0（pure1.5MWX3-ECH）to2.6（2MWNBI）,andcouldevenreachtheidealMHDlimit（∼3）resultingfromthefastparticlecontribution.Fastionslowingdowntimesinsuchregimesareoftheorderof,i.e.shorterorcomparablewiththebulkplasmaenergyconfinementtime,so,perturbationoftheionenergyMaxwelliandistributionbyfastionsisexpectedtobesmall（asinafusionreactor）.

2.2.X2-ECandNBIheating

ModellingofNBheatinginlowdensityregimeswasperformedfor2MWX2-ECheatedL-modereferencedischarge（#31761,No.2.0）.IncreaseoftheNBdepositedpowerperplasmaionatlowdensityresultsin∼2timeslower（）thaninhighdensityregimeNBIpowerrequiredtoaccessof（scenarios2.1and2.2andFig.3）.Near-normalNBinjectioncannotbeconsideredhereduetohighershine-throughlosses,resultinginfirstwalloverheatoftheTCVcentralcolumn.ASTRAsimulationsconfirmearlierexperimentalandnumericalstudiesoffastionorbitlossesontheTCV[13].Atlowplasmacurrent,fastionorbitlossesareextremelyimportantandbecomesubstantialforcounter-IpNBinjection（Fig.4）;lossesincreaseathighionenergy（32%forD-NBand59%for,scenarios2.4and2.7）andforhigherNBatomicmass.

NBinjectionatlowplasmadensityandcurrentprovidesthepossibilitytostudythefastionandMHDphysics.Intheunfavourablescenario（like2.4）,thedeliveredbytheNBpowerleadstothecreationofastrongfastionpopulationwithastoredenergyoffewtenskJthat,atlowcurrent,significantlycontributestotheidealMHDˇlimit.Fastparticleinstabilitieswoulddominatetheplasmabehaviourundertheseconditions[5].

3.Neutralbeamsinjectionlayout

TCVwasnotoriginallydesignedforneutralbeamheatingalthoughseveralrelativelywidemachinemidplanelateralportswereimplementedforgeneraldiagnosticflexibility.Thelocationofmagneticfieldcoils,forwhichmodificationisnotfeasible,andtheexistingsupportstructuresaremajorproblemsforNBIplasmaaccess,inparticularforthetangentialinjectiondirection.AccessforNBinjectorsthrough15cmdiameterports

withnearnormalinjection（tangencyradius）andthroughasingleØ10cmaperturenear-tangentialinjectionportwiththeaxispassingneartheinnerwallathasbeenanalysedin[13].Shinethroughforisworkableatthehighdensities;NBusageatlowdensitiesis,however,severelylimitedbyexcessiveshine-throughandhighinnerwallpowerloads.Themaximalacceptablepowerloadof7.6MW/fora1sdurationleadstotemperatureriseofgraphiteinnerwalltiles[14]of1000Kcorrespondingtoshine-throughofthe1MWbeamwiththe15cmfoot-printsize.

Amodelofaneutralbeamwithgeometricfocussingandangulardivergence[15]wasperformedtocalculatethebeamtransmissionandpowerloadonthecriticalscrapersintheNBIduct.Theacceptable∼80%beampowertransmittedintothetokamakfor1MW,,1sbeamwith200mA/cm2extractioncurrentfromtheionopticalsystemlocatedatabout250cmfromtheTCVportisfeasibleonlywithlowbeamdivergence:

0.7/0.8。

forØ10/15cmductaperturesrespectively.ThetransmissionofthehighpowerNBthroughnarrowportsdemandshighcurrentdensity,lowdivergenceneutralbeaminjectoronlyreachable,atpresent,bylowercurrentdiagnosticneutralbeams.ToallaytheserequirementsonbeamdivergenceandcurrentdensityamodificationTCVvacuumvesseltocreatenewport（s）,specificallydesignedforNBHandfittedbetweenmagneticfieldcoils,isconsidered.TheavailablegapsbetweentoroidalandpoloidalmagneticfieldcoilsattheTCVmidplaneare22cminverticaland38cmintoroidaldirection.Thedesignofductwithinner

minimalapertureof20cm,wallthickness1cmand