英文原文AscopingstudyoftheapplicationofneutralbeamheatingontheTCVtokamakAlexanderN.Karpushova,?,BasilP.Duvala,RenéChavana,EmilianoFableb,Jean-MichelMayora,OlivierSautera,HenriWeisenaaEcolePolytechniqueFédéraledeLausanne(EPFL),CentredeRecherchesenPhysiquedesPlasmas,AssociationEuratom-ConfédérationSuisse,CH-1015Lausanne,SwitzerlandbMax-Planck-InstitutfürPlasmaphysik,Euratom-IPPAssociation,Boltzmannstra遝2,D-85748Garching,GermanyArticleinfoArticlehistory:Availableonline17March2011Keywords:TCVtokamakNeutralbeamheatingAbstractTheTCVtokamakcontributestothephysicsunderstandingoffusionplasmas,broadeningtheparameterrangeofreactorrelevantregimes,byinvestigationsbasedonanextensiveuseoftheexistingmainexperimentaltools:flexibleshapingandhighpowerrealtime-controllableelectroncyclotronheating(ECH)andcurrentdrive(ECCD)systems.AproposedimplementationofdirectionheatingontheTCVbytheinstallationofaneutralbeaminjection(NBI)withatotalpowerofwouldpermitanextensionoftheaccessiblerangeofiontoelectrontemperatures()towellbeyondunity,dependingontheNBI/ECHmixandtheplasmadensity.ANBIsystemwouldprovideTCVwithatoolforplasmastudyatreactorrelevantratios～1andininvestigatingfastionandMHDphysicstogetherwiththeeffectsofplasmarotationandhighplasmaˇscenarios.ThefeasibilitystudiesforaNBIheatingonTCVpresentedinthispaperwereundertakentoconstructaspecificationfortheneutralbeaminjectorstogetherwithanexperimentalgeometryforpossibleoperationalscenarios.1.IntroductionTCVisacompact(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.ScenariosofNBIheatingexperimentsExperimentalscenariosfortheNBIexperimentsontheTCVarestronglylinkedtolimitationsimposedbyECHandECCD.FortheeITBsandfullynon-inductivescenariosonTCV,theaccessibleplasmadensityislimitedbytheX2cut-offincurrentdriveandelectronheatingexperiments.Conversely,efficientX3depositionisobtainedforelectrondensityintherangeofandTheASTRAcode[8]wasusedtosimulatetheplasmaresponsetoneutralbeamheatinginthegeometryoftheTCVtokamak.ThecodesolvesequationsforelectronandiontemperatureandplasmacurrentdensitywiththeprescribedelectrondensityprofileandtotalplasmacurrenttakenfromTCVexperiment.Theuseoftheneoclassicalionheatconductivity[9]givesthatismatchedtotheCXRS[10]measurement.Theexperimentalelectronheatconductivitywasnormalisedtoobtaintheenergyconfinementtimepredictedbypowerlawscalings[11]:IPB98(y,2)forELMyH-modeandstandardpowerlawregressionforL-mode.TheECpowerdepositionprofilewascalculatedbytheTORAYray-tracingcode.2.1.HighdensityELMyH-moderegimeThetargetparametersformodellingweretakenfromOhmicandX3heated(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-ECandNBIheatingModellingofNBheatinginlowdensityregimeswasperformedfor2MWX2-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.NeutralbeamsinjectionlayoutTCVwasnotoriginallydesignedforneutralbeamheatingalthoughseveralrelativelywidemachinemidplanelateralportswereimplementedforgeneraldiagnosticflexibility.Thelocationofmagneticfieldcoils,forwhichmodificationisnotfeasible,andtheexistingsupportstructuresaremajorproblemsforNBIplasmaaccess,inparticularforthetangentialinjectiondirection.AccessforNBinjectorsthrough15cmdiameterportswithnearnormalinjection(tangencyradius)andthroughasingle?10cmaperturenear-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。for?10/15cmductaperturesrespectively.ThetransmissionofthehighpowerNBthroughnarrowportsdemandshighcurrentdensity,lowdivergenceneutralbeaminjectoronlyreachable,atpresent,bylowercurrentdiagnosticneutralbeams.ToallaytheserequirementsonbeamdivergenceandcurrentdensityamodificationTCVvacuumvesseltocreatenewport(s),specificallydesignedforNBHandfittedbetweenmagneticfieldcoils,isconsidered.TheavailablegapsbetweentoroidalandpoloidalmagneticfieldcoilsattheTCVmidplaneare22cminverticaland38cmintoroidaldirection.Thedesignofductwithinnerminimalapertureof20cm,wallthickness1cmand3cmgapstotoroidalfieldcoils,beamaxistangencyradiusof74cm(Fig.5)wasfoundtobefeasibleandpermitstotransmit>90%oftheNBpowertotheplasmafor1MW,deuteriumbeamwithdivergence(reachableforheatingbeams).TherelationbetweenandbeamductaperturehorizontalsizeforchosenductwallthicknessandgapstotoroidalcoilsisshowninFig.6.Toreducebeamblockingbydesorbedgasinthenarrowestpartofthebeamduct(closetothetokamakentrance),differentialductpumpingisrequired.ThisgeometrycouldpermittwoNBinjectors(aiminginco-andcounter-currentdirections)onthesameport.Withproperpoweradjustment,onecouldobtainscenarioswithbalancedmomentumtransfertotheplasma.4.ConclusionInstallationof1MW,,deuterium,tangential(basicreference)neutralbeaminjectorwouldsignificantlyincreasetheexperimentalcapabilityoftheTCVtokamakbyextendingtheoperationaldomainathigherratioandplasmapressureandwideningH-modeoperationaldomain(especiallyathighdensity).1MWofinjectedpowerissufficienttoaccess,takingintoaccount20%CXfastionlossesonbackgroundneutrals.Twobalancedco-andcounter-Iporientatedinjectorswithtotalpowerof2MWwouldpermittheinvestigationoftheeffectsofNBinducedplasmarotation,toreachvratio≥2andstudyfastionbehaviorandMHDphysicsinscenariossuchasstationaryELMfreeH-modesandfullynon-inductiveelectroninternaltransportbarriers.Loweringthebeamenergyresultsinadecreaseoftheon-axisionheatingpowerdensitybybroadeningtheNBdepositionprofile.Athigherbeamenergies,fastionorbitlossesstronglyreducetheheatingefficiency,especiallyforcounter-beamalignment(Figs.2and4).Foragiveninjectionenergyandtargetplasmaparameters,thefractionofNBpowerdeliveredtobulkionsishigherandshine-troughlossesarelowerfordeuteriumbeamthanforhydrogen(Fig.4).Duetounacceptableshine-throughpowerloadonthecentralcolumn,onlydouble-pathtangentialNBinjectionisacceptableforintermediateandlowplasmadensities(<4×1019m?3,fordeuteriumbeam).ThecapabilityoftheNBIoperationtousehydrogenionsisessential(1)foron-axisionheatingathigh()plasmadensityand(2)toreduceorbitlossesofcounter-injectedfastionsatlow(plasmacurrent.Adjustablebeamenergyof15–30andlikelyawiderrangeshouldsatisfytheconceptofTCVaveryflexibletokamakandpermitstoadjustbeampowerbysimultaneouschangeofbeamenergyandioncurrent(maintainingoptimalperveance,relationshipbetweenbeamenergyandcurrent).AcknowledgmentsThisworkwassupportedinpartbytheSwissNationalScienceFoundation.TheauthorsaregratefultoProf.A.A.Ivanov,Prof.V.I.DavydenkoandDr.T.D.Akhmetovforusefuldiscussionsanddevelopingoftheneutral-beampropagationcode[15].翻譯在TCV托卡馬克中用中性束加熱的一般性研究摘要：TCV托卡馬克以現有的實驗工具（可形變高功率實時可控的電子回旋共振加熱裝置（ECH）和電流驅動系統（ECCD）為基礎進行大量研究，對聚變等離子體的物理解釋和擴展聚變堆相對溫度的范圍有貢獻。用總功率為的的中性束注入裝置（NBI），預期可實現在TCV中對離子進行直接加熱，使得依賴于NBI/ECH和等離子體密度的離子與電子溫度之比的范圍擴大到（）超過單位值。NBI系統將為TCV對的聚變堆內等離子體的研究和快子MHD物理結合等離子體旋轉效應高β值的研究提供有力工具。本文對TCV中NBI加熱的可行性研究，是通過建立專門的中性束注入系統和適用于可操縱情況的實驗幾何尺寸進行的。關鍵詞：TCV托卡馬克，中性束加熱（NBH）1.序總TCV是一種結構緊湊（主半徑，次半徑，環狀磁場，等離子體電流），高度拉伸（管拉伸率為3）的環狀聚變實驗裝置。高功率實時可控，注入波在第二（X2，3MW）和第三（X3,1.5MW）電子回旋諧振頻率構成主要的加熱方式（ECH）。在等離子體中進行非感應電流驅動（ECCD）等離子體的電子密度為,電子溫度為，離子溫度，可形變等離子體和高功率ECH系統被用于托卡馬克許多方面的研究。高功率X2-ECH對于相對密度低的TCV等離子體，將不容許在離子電子溫度比的情況下操作，因為電子離子的經典庫倫碰撞熱平衡時間比特征約束時間長得多。在功率為MW量級的情況下對離子進行直接加熱，可使增大超過單位值，從而填補了目前占主導地位的電子加熱實驗和聚變堆之間的差距。離子與電子溫度之比在從現有實驗到聚變等離子的輸運機制的研究計劃中起特別重要的作用。在離子溫度梯度（ITG）和束縛電子模式（TEM）之間的轉變起關鍵作用，決定了紊流能量的輸運機制。在DIIF-DH-模式實驗中當增加可觀察到離子和電子能量輸運的減小。因此NBI加熱容許TCV等離子體的β值更高，接近理想極限，甚至在高拉伸率裝置中可超過理想極限。將高速原子束注入托卡馬克裝置是一種可能的好的輔助加熱方法。但是如果快離子能量低于臨界值（對于氫原子束和氘等離子體Ecrit,）能量和動量輸運主要由大量離子完成，將出現電離、電荷交換、快原子束被束縛等現象。預期的NBI系統只要旋轉等離子體控制TCV已被很好的診斷，也將為TCV提供研究快離子和研究相關的MHD物理提供工具。其中ITB附近的環狀旋轉行為尤為重要，因為它將影響觸發或持續勢壘。目標等離子體能夠包括類ITERH模式形狀和目前只在歐姆范圍內接近的先進形狀。2.NBI加熱實驗的相關情況TCV托卡馬克裝置中的實驗參數與ECH和ECCD的受迫極限有很大關系。對于TCV中的elTBs和完全非感應情況，可得到的等離子體密度被X2的電流驅動系統和電子加熱裝置所限制,與此相反，X3的有效電子密度要求在的范圍內，要求電子溫度。ASTRA被用來模擬在TCV的幾何尺寸條件下，等離子體對中性束加熱行為的反應。這一程序通過求解，在實驗中已得到的電子密度和總等離子體電流的條件下，離子和電子的溫度以及等離子體電流密度。發現利用新古典離子加熱電導率（）得到的值與CXRS的測量值相符。實驗電子加熱電導率（）被規范后可以得到可由得到能量約束時間（IPB98（y,2）ELMyH模）。ECH的能量沉積由TORay射線跟蹤軟件計算得到。2.1高密度ELMyH模式范圍模型的目標參數是通過歐姆加熱和X3加熱釋放的定態ELMyH-模式、對于切向入射的能量為的氘中性束約有95%被等離子體吸收。模擬表明用0.8MW中性束注入（NBI）和1.3MW的X3-ECH可得到，通過增大中性束的功率（）或減小X2-ECH的功率，使也能達到。中性束背景情況下快離子電荷交換損失（CX）與第一層循環條件，背景原子密度。通過ECRENE模型得到，將使中性束加熱效率減小將近15%,中性束電荷交換損失率＜2%,可忽略不計。2.2X2-EC和中性束加熱低密度中性束加熱模型，增加中性束能量沉積功率使得低密度等離子體中的離子比高密度中的低2倍。NBI系統的功率要求接近由于更高的（）的shine-through損失，將導致TCV中心圓柱第一層被過度加熱，故在此不能將中性束認為是近似正常中性束注入。ASTRA模擬值與更早的TCV中快離子損失的實驗數值相符合。在低等離子體電流情況下，快離子的軌道損失是極其重要的，而且使NB注入變得。能量損失隨中性束原子質量的增加及離子能量的增高而增加。低密度等離子體和低等離子體電流的中性束注入，為快離子和MHD物理的研究提供了可能。當不合適的參數（如2.4）由MD傳遞的()功率導致產生了能量為幾十千焦的大量快離子，