Fusion Engineering and Design

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ContentslistsavailableatScienceDirect

Fusion

Engineering

and

Design

j ou rn a l h o m epa g e :w w w . e l s e v i e r . c o m / l o c a t e / f u s e n g d e s

Heating

&

current

drive

efficiencies,

TBR

and

RAMI

considerations

for

DEMO

T. Franke

a,b,∗

_,

_P.

_Agostinetti

c

_,

_K.

_Avramidis

d

_,

_A.

_Bader

b

_,

_Ch.

_Bachmann

a

_,

_W.

_Biel

e

_,

T. Bolzonella

c

_,

_S.

_Ciattaglia

a

_,

_M.

_Coleman

a

_,

_F.

_Cismondi

a

_,

_G.

_Granucci

f

_,

_G.

_Grossetti

g

_,

J. Jelonnek

d

_,

_I.

_Jenkins

h

_,

_M.

_Kalsey

h

_,

_R.

_Kembleton

h

_,

_N.

_Mantel

h

_,

_J.-M.

_Noterdaeme

b,k

_,

N. Rispoli

f

_,

_A.

_Simonin

i

_,

_P.

_Sonato

c

_,

_M.Q.

_Tran

j

_,

_P.

_Vincenzi

c

_,

_R.

_Wenninger

a,b

a_EUROfusion_Consortium,_{Boltzmannstr.}_2,_D-85748_Garching,_Germany

b_{Max-Planck-Institut}_für_{Plasmaphysik,}_{Boltzmannstr.}_2,_D-85748_Garching,_Germany

c_Consorzio_RFX_(CNR,_ENEA,_INFN,_Università_di_Padova,_Acciaierie_Venete_SpA)_Corso_Stati_Uniti₄_–_Padova,_Italy

d_IHM,_Karlsruhe_Institute_of_Technology_(KIT),_Kaiserstr._12,₇₆₁₃₁_Karlsruhe,_Germany

e_Institute_of_Energy-_and_Climate_Research,_{Forschungszentrum}_Jülich_GmbH,_Germany

f_Institute_of_Plasma_Physics_“P._{Caldirola”,}_National_Research_Council_of_Italy,_Milan,_Italy

g_IAM-AWP,_Karlsruhe_Institute_of_Technology_(KIT),_Kaiserstr._12,₇₆₁₃₁_Karlsruhe,_Germany

h_Culham_Centre_for_Fusion_Energy,_Culham_Science_Centre,_Abingdon,_Oxfordshire,_OX14₃₅₁₂₇_3DB,_United_Kingdom

i_CEA-IRFM,_F-13108_{Saint-Paul-Lez-Durance,}_France

j_SPC_Swiss_Plasma_Center_(SPC),_EPFL,_CH-1015_Lausanne,_Switzerland

k_Department_of_Applied_Physics,_University_Ghent,_Ghent,_Belgium

h

i

g

h

l

i

g

h

t

s

•_New_H&CD_concepts_with_high_wall-plug_efficiencies_are_under_{investigation}_for_DEMO. •_The_present_estimates_regarding_the_impact_on_the_TBR_of_the_H&CD_systems_are_promising. •AsinitialtargetthemaximumreductionoftheTBRduetotheintegrationofsystemsisTBR≤0.08.

•_RAMI_is_considered_from_the_beginning_and_proposals_were_made_how_to_increase_HCD_system_reliability. •_New_proposal_for_clusters_for_EC_and_modular_ion-sources_for_NB_are_made_to_improve_DEMO_reliability.

a

r

t

i

c

l

e

i

n

f

o

Articlehistory:

Received3October2016

Receivedinrevisedform31January2017

Accepted3February2017

Availableonline13February2017

Keywords: DEMO

heatingcurrentdrive

efficiency

Tritiumbreedingratio

RAMI

a

b

s

t

r

a

c

t

Theheating&currentdrive(H&CD)systemsinaDEMOnstrationfusionpowerplantareoneofthemajor energyconsumers.DuetoitshighdemandinelectricalenergytheH&CDefficiencyoptimizationisan importantgoalintheDEMOdevelopment.

TheH&CDpowerforDEMO,basedonphysicsscenariosforthedifferentplasmaphases,isneededfor plasmainitiationphases(incl.breakdown),currentramp-up,heatingtoH-mode,burncontrol,controlled currentramp-down,MHDcontrolandotherfunctions.Plasmacontrolwillneedsignificantinstalled H&CDpower,thoughnotcontinuouslyused.

Previously,intheDEMO12015baselinedefinitions,optimisticforecastedH&CDefficiencieshadbeen assumedinthecorrespondingsystemcode(i.e.PROCESS)module.Realizingthatthereisahigh uncer-taintyintheassumptionstheefficiencieshavebeenmodifiedandtheimpactontheDEMOpowerplant andbasictokamakconfigurationarediscussedinthisarticle.

AcomparisonofthevariousH&CDsystemsNBI(NeutralBeamInjection),ElectronCyclotron(EC),Ion Cyclotron(IC)intermsofimpactonTritiumBreedingRatio(TBR)duetovariousopeningsfortheH&CD frontendcomponentsinthebreedingblanket(BB)ispresented.

Forincreasingthereliabilityasmajorfeaturesthepowerpersystemunitandtheredundancyare identifiedleadingtoanewproposalforclustersforECandmodularion-sourcesforNB.

∗ Correspondingauthorat:EUROfusionConsortium,Boltzmannstr.2,D-85748

Garching,Germany.

E-mailaddress:[email protected](T.Franke).

http://dx.doi.org/10.1016/j.fusengdes.2017.02.007

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1. Introduction

EUROfusion is undertakinga fusion energy researchproject,

whichiscalledDEMO,aDEMOnstrationfusionpowerplant.DEMO

shalldeliverasfirstofitskind∼300–500MWofelectricalenergyto

thegrid.Thedesignhasstartedin2014andisinapre-conceptual

designstate.Duringthisphasetheteamsdevelopdifferentsystems

tounravelpossibledesignchoicesandtofindthebestsolutionsand

combinethemtoaDEMOwhichisTritiumself-sufficientandhighly

reliable.

AfuturefusionpowerplantDEMOisconsideredasasustainable

andmoreenvironmentalfriendlysolutioncomparedtoany

exist-ingconventionalpowerplanttechnology(e.g.fission,coal)inthe

worldandisindependentofnaturalfluctuations(likewind,solar).

Toheattheplasma,extendthepulsetimeandprovidevarious

controlfunctionsthreeH&CDsystemsaredevelopedfor

integra-tion inDEMO, namely:ElectronCyclotron (EC)System,Neutral

BeamInjection(NBI)SystemandIonCyclotronRangeofFrequency

(ICRF)System.TheWorkprogrammedoesnotincludeLowerHybrid

waves.TheDEMOH&CDmixshallbedefinedataboutendof2024,

inthemiddleoftheconceptualdesignphase.

ThepresentbaselineunderdevelopmentisDEMO1,apulsed

machine.Aspossiblealternativeasteady-statemachineDEMO2is

understudywithhigherandmoredemandingphysicsand

engi-neeringassumptions.

2. Heatingandcurrentdrive(H&CD)efficiencies

Theefficienciesarediscussedindetailine.g.[1]and[2].Both,

thecurrentdrive&coupling(physics)andwall-plug(systemsor

transmission)efficiencieshaveimpacttotheDEMOdesign,

espe-ciallyforasteady-statedevice,inwhichtheohmicplasmacurrent

needstobereplacedcompletelybyauxiliaryCDpower.

Tomoveclosertoamaturedesignitisproposedtousemore

realisticstate-of-the-artsystemsefficiencies(ITER-likevalues;EC

35%andforNB25%),thiswillleadwithanassumedmixof20MW

ECplus30MWNBIpowerduringflattoptoanaveragesystems

efficiencyof29%.Thisisareductionofabout10%toformer

assump-tions.Thesenumberswillbeupdatedbasedonnewandvalidated

findings andaminimumTechnical ReadinessLevel(TRL)ofthe

systems,ideallyhavingbeentestedinarelevantenvironment.

Forapulsedmachine(pulseduration>2h)anefficiency

reduc-tion − as recently studiedwith PROCESS Code − of either the

physicsor transmissionefficiency by 10%couldin principle be

compensatedbyincreasingthefusionpower/plasmavolumeand

hencethemajorradiusofthetokamakby∼0.1mbutwithnegative

consequencesontheoverallmachinecosts.

Thetargetoftheworkpackage(WP)H&CDistocarryout

inten-siveR&D onwall-plugefficienciesand conductstudies onhow

to improve physicsbased efficienciesin collaboration withthe

PowerPlantPhysics&Technology(PPPT)departmentof

EUROfu-sion(Table1,Fig.1).

ThetotalamountofinstalledH&CDpowerofDEMOismainly

drivenbythepowerneededfortheH-modeaccess(LH-threshold)

andthecontrolduringburnphase[3].Thisfieldofactivityisunder

preciseevaluation.

TheDEMOH-modeaccessduringtheplasmaramp-upwas

sim-ulatedwith‘METIS’,afasttokamaksimulator,andleadsinviewof

uncertaintiesto100–150MWinjpowerapplyingtheITPA-Martin

scaling[4].

AdditionalMHDcontrolpowerforNeoclassicalTearingModes

(NTMs)of<10-15MWinjisneeded[5].

As longastherequired total injectedH&CD poweris under

studyeachH&CDsystem(EC,NBI,andICRF)isdevelopedaimingfor

∼50MWinjpower,knowingthattheamountofinstalledpowerwill

bedecidedatalaterstateoftheDEMOconceptualdesign(Table1,

Fig.1).

3. Tritiumbreedingratio(TBR)considerationsforH&CD

AsinitialtargetthemaximumreductionoftheTBRduetothe

integrationofauxiliarysystemsinthebreedingblanketwasdefined

asTBR≤0.08.Thisnumberisassumedtobeequallyshared)by

(i)allH&CDsystems&(ii)allDiagnosticsystems.Thevaluemight

bemodifiedinthefuturedependingonthelocaltritiumbreeding

performance ofthebreedingblanket.Theintegrationofthe

dif-ferentH&CDsystemsintoDEMOiscurrentlystudiedbyH&CDin

collaborationwiththeBreedingBlanketproject[7].

SomeinitialresultsandtheirTBRimpactarediscussedbelow.

3.1. EClauncher

ThecurrentlystudiedECportplugdesignoptionsare:(i)

Blan-ketIntegratedDesign(pluggedintotheblanket)and(ii)Separated

Blanked Module (SBM) (cf. Fig. 2). For the SBM two different

arrangementsofthelaunchersareunderassessment,stacked1×8

or2×4(rowsxcolumns).Thedesigndependsalsoonthelauncher

technologywiththefocusontheRemoteSteeringAntennae(RSA)

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Table1

Mainparametersofcurrentlyavailable(quasioff-the-shelf)ITER-likesolutionsversusnewDEMOdesigns(oneexampleofthemostpromisingcandidatesolutionsforthe

DEMOECandNBIsystemsareshownbelow,someothersareunderdevelopment).

ECITER ECDEMO(understudy) NBIITER NBIDEMO(understudy)

170GHzgyrotrons 170/204GHzgyrotrons Singlesource(n=1) Modularsources

(n=20) 1MW 2MW 1000keV,17MW 800keV,17MW Efficiency35%(system), (Gyrotron ∼50%+TL+MOU+Launcher+PS) Efficiency∼50% (system),(Gyrotron ∼60%+TL+MOU+Launcher+PS) Efficiency25%(system) (Neutralizer∼55%, stripping/halo70%, etc.) Efficiency∼50% (system)(Neutralizer ∼70%,stripping/halo 90%,etc.) EvacuatedTL Evacuated Quasi-opticalTL Gas-Neutralizer Photo-Neutralizer

Front-steeringantenna Remote-steering

antenna

Cryopumps NEGpumps/Hgpump

Fig.2. ECconceptuallauncherdesignexample.

Fig.3.ICRF360◦_TWA_antenna₍₁_of₁₈_sectors),_RF_feeding_scheme_still_to_be_defined.

oralternativelyonstep-tunablegyrotrons(requiringBrewster

win-dows),oracombinationofboth.

Neutroniccalculations[8]resultinTBRof∼0.0175−∼0.035

for50MW_injwithpowerlaunchedthrough5equatorialports.

3.2. ICRFantenna

TheTBRoftheICRFtravellingwaveantenna(TWA)forDEMO

(cf.Fig.3)quantifiedin[9]hasvaluesoflessthan∼0.006,depending

ontheblanketconcept.Thecalculationswerehoweverdoneforthe

antennaonly,neglectingtheRFfeeders.

Differentfeedingschemes(numberandsizeofRFfeeders)and

relatedintegrationissuesareunderassessment.Thefeedingcould

bedone(i)throughtheCentralOutboardSegment(COBS)ofthe

BreedingBlanket(BB),alternatively(ii)throughboththeRightand

LeftOutboardSegments(ROBSandLOBS)oftheBB.Forboth

alter-nativesa1linefeedingora2linefeedingisactuallyconsidered.

Fig.4. NBblanketintegrationproposal.

Thetotalnumberoffeedersmayvarybetween36(COBwith1

linefeeding)upto144(ROBSandLOBSwith2linefeeding).The

finalTBRoftheTWAwithRFfeedersis notyetavailableand

dependsonwhichfeedingconfigurationischosen.

3.3. NBIduct

DependingontheintegrationstrategytheTBRisexpected

tobeintherange of∼0.002to∼0.006for oneNBinjector. For

thepresent assumption of 3injectors (power launchedfrom 3

inclinedequatorialNBports)andapartiallyvoidedportdesign(cf.

Fig.4),theNBITBRcanbeexpectedtobeintherangeofabout

0.006–0.018for50MWinj.

4. RAMIapproachforH&CD

Inanuclearpowerplantenvironmentmaintenanceperiodsare

optimised.ToensureDEMOavailability targetaremet,H&CDis

applyingfromtheconceptstageRAMImethodology.Thefollowing

tasksareproposed.

Firstly,definetheinterfacesoftheH&CD.Anexampleisshown

inTable2basedontheDEMOPlantBreakdownStructure(PBS).

Secondly,definetheFunctionalBreakDownStructure(FBS)of

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func-Table2

Exampleofinterfacesmatrix.

DEMOPBS(partially) EC NB IC

MagnetSystem x x x

VacuumVessel x x x

Divertor

ThermalShields

TritiumFuellingVacuum(TFV) x x x

Table3

ExampleofH&CDprimaryfunctions.

FunctionN◦ _Functions

1 Tocontrolthefuelmix

1.1 Toheatthefuelmix

1.1.1 Toheatfuelmixtobreakdown

1.1.2 ToheatplasmatoHmode

1.1.3 Toheatplasmatoburn

1.2 Todrivetheplasmacurrent

... ....

2 Toconditionthewall

Table4

Exampleofconstraintfunctions.

FunctionN◦ _Interaction_with_PBS _Constraints_function

n MagnetSystem Tofitthroughmagnetic

coilsystem

n+1 VacuumVessel Tomaintain&control

vacuumattheinterface

withplasmachamber

Table5

ExamplesforaiminghigherH&CDreliability.

ECSystem NBISystem ICRFSystem

Clusteredsolution (cf.Fig.6)to minimisethe numberofEC components Increasenumberof sources(stacked 2×10modular sources)insteadof singlesource. TWAasintegrated partofthe breedingblanket

withthesame

reliabilityasthe

blanket.

Maximizethe

systemsreliability,

∼100%achieved

afterinitialburnin

Decreasebeam

energyfrom1MeV

(ITER)to800keV

(DEMO)

Avoidantenna

arcingduetolower

powerdensity

(360◦_TWA)

tions(cf.Table4).Foreachinterfaceidentifiedaminimumofone

constraintfunctionshouldbeattributed.

Thirdly,attributetheprimaryfunctionstotheH&CDsystem.

Fourthly,defineatwhichmachinestatethesystemis

perform-ingthefunction.

The following steps will involve a furtherdecomposition of

thefunctionsatthesubsystemlevelfollowedbyaFailureMode

EffectsAnalysis(FMEA).Havingaclearunderstandingofthefailure

modeatanearlyconceptstageisparamounttointegrate,at

mini-mumcost,thereliability,maintenance,monitoringandinspection

requirementsinthedesign.TheFMEAwasstartedtounderstand

thefailuremodesbeforequantifyingthem.Howevertheseratings

arenotyetfinallysettledandchangeispossiblebeforetheFailure

ModeEffectsandCriticalityAnalysis(FMECA)isimplemented.

4.1. ExamplesofreliabilitystudiesforH&CD

Atthisstageoftheproject,knowingthattheavailabilityisa

crucialfactorforaDEMOoperation,theRAMIworkwasfocused

firstonthereliability,furtherstudieswillfollow.Newproposalsto

improvethereliabilityoftheDEMOauxiliaryheatingsystemsare

Fig.5. Simple(ECL)Configuration.

Fig.6.ClusterECLine(ECL)Configuration.

Table6

ClusterECLconfigurationwithback-upitems(markedbold).

n+m Numberof

ECLs

RECSa(in%) MTBF(in

pulses) Numberof Gyrotrons 1+1 28+1 99,9601 2507 58 2+1 14+1 99,9896 9606 45 3+1 10+1 99,9945 18291 44 4+1 7+1 99,9972 35852 40 5+1 6+1 99,9979 47777 42 6+1 5+1 99,9985 66830 42 7+1 4+1 99,9987 79870 40 8+1 4+1 99,999 100198 45 9+1 4+1 99,999 100200 50

a_Assuming_lifetime_after_initial_burn_in_and_before_end_of_lifetime_cycle.

shownbelow(cf.Table5)togiveindicationswithafewexamples

aboutthetypeanddirectionofthestrategy.

TheclusteredsolutionfortheECsystem(ECS)willbediscussed

in somemoredetailbelow. Fig.5 showsfirsttheprincipleofa

simpleElectronCyclotronLine(ECL)whichiscommonlyusedin

presentdayexperiments.

AclusteredECLisshowninFig.6.andiscomposedof1ton

componentsandB1toBmbackupcomponents.

Forthecasen=1(andwithoutbackupcomponentsm=0)the

ECLis−exceptthePowerSwitch(PS)−thesameasinFig.5with

only1PSU(PowerSupplyUnit),1Gyrotron(G),1TransmissionLine

(TL)and1Launcher(L).ForahighernumberofEClines(n>1,m≥1)

thereliability RECSof theECS increaseswhereasthenumber of

itemscanbereducedasshowninTable6.

TheinputvaluesforthestudyaresimilartoITER-assumptions

(componentR&Dtargets)[10],andsupposedtohaveareliability

centredmaintenance(RCM)approachforDEMO:G98.0%,TL99.9%,

L99.9%,PSU100.0%.

Assumingasingleredundancy(m=1)(cf.Table6)showswhich

reliabilityRECSandMTBF(MeanTimeBetweenFailures)[11]could

beachieved.Thevaluesreportedaretheresultofanoptimization

process,aimedatidentifyingtheminimumnumberofclustersto

ensureaMTBFof>1000,whichcanbeseenas3monthsofoperation

withoutfaults.Thebestconfigurationcanbefoundfor4+1ECLs,

inwhichthenumberofGyrotronsis40(alsoforLandPS).

FormerintegrationstudiesshowedthatoneECportplugis

capa-bletocollectmax.8EClaunchers(cf.chapter3.1).Assumingthe

reliability targetsare mettheECSwillneed5equatorialDEMO

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5. Summary

NewH&CDconceptswithhighwall-plugefficienciesareunder

investigation.Thepresentestimatesregardingtheimpactonthe

TBRoftheH&CDsystemsarepromising.Detailedstudiesare

ongo-inghand-in-handwiththeblanketintegration.RAMIisconsidered

from thebeginning and proposals weremade how toincrease

presentreliabilitylimitations.

Acknowledgments

This work has been carried out within the framework of

the EUROfusionConsortiumand hasreceivedfundingfromthe

Euratomresearchandtrainingprogramme2014–2018undergrant

agreementNo633053.Theviewsandopinionsexpressedhereindo

notnecessarilyreflectthoseoftheEuropeanCommission.

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