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RESEARCHPROJECT

TITLE:

SCIENTIFICPREMISES:

MAINSUBJECTS:

THECURRENTRESEARCHCONDITIONANDLEVELOFTHERESEARCHPROJECTATHOMEANDABROAD:

CentralfuelingisdesiredforfutureDTfusionreactorslikeChineseFusionEngineeringTestReactor(CFETR)tooperatesafelyandeconomically.Achievingtritiumcentralfuelingcandecreasetritiumretentionintheplasmafacingcomponents,andcanincreasetritiumburn-upfractionwhichisadvantagetosimplifyingthedesignandconstructionoftritiumbuildingreducingthecostofthefusionpowerplant.

Comparingtotraditionalgaspuffing,pelletfuelinghashigherfuelingefficiencybecauseofthedeeperpenetrationofthepellets.Associatedwiththisdeeppenetration,pelletinjectioncancauseapeakdensityprofile,andimprovetheconfinementpropertieswhichisbeneficialforreactorstooperateatahighdensityscenario.Forthesereasons,pelletinjectionisconsideredastheprimaryfuelingmethodinfuturefusiondevices.

Studyonpelletfuelinghasbeenmakingaconstantprogressbothexperimentallyandtheoreticallyformorethanfourdecades.Pelletwasinjectedfromlow-fieldside(LFS)inearlyexperiments,andanincreasingfuelingefficiencywasobservedwithincreasingpenetrationdepth.In1990s,LangPTandcollaboratorsfoundthatpelletslaunchedfromHFSpenetratedeeperthanthoselaunchedfromLFS,whichwasduetothedriftoftheablatantdowntothemagneticfieldgradientandwasconfirmedinDⅢ-Dexperimentssoonafterwards.Duetoitsdeeperpenetration,HFSpelletfuelingisadoptedbyITERdesign.However,thepelletvelocityislimitedto300m·s-1bycollisioninthecurvedtubethroughwhichthepelletsaretransferredtotheHFS.What’smore,ithasahotedgeinITERplasma,soit’spredictedthatpelletscannotpenetratemuchdeeplyeveniflaunchedfromHFS.

Ontheotherhand,effortsontheoryandsimulationofpelletfuelingisdevotedtohelpunderstandingpelletfuelingprocess.Ontheablationprocess,Parksdevelopedasimpleneutralgasshielding(NGS)modelinlate1970s,whichcanreproducesatisfactorilytheexperimentdataofpelletpenetrationdepthintheInternationalPelletAblationDatabase(IPADBASE)andiswidelyused.Afterthat,othermodelstookintoaccountmoresophisticatedeffects,suchascoldplasmashielding,electrostaticshielding,magneticshielding,Maxwelliandistributionofambientplasma,atomicprocess,energeticparticles,anisotropicheatflux,warpingofthepelletandsoon.Asfortheablatantdriftdowntothemagneticfieldgradient,it’sgeneralbelievedtobeaE×Bdriftandinasimplepicturetheelectricfieldisdeterminedbythebalancebetweenthe?B-induceddriftandthepolarizationdriftofparticlesintheablatantcloud.

Thoughstudyonpelletfuelinghasmadeagreatprogressbothexperimentallyandtheoreticallywhenappliedtopresent-daytokamaks,thingsmaybecomedifferentwhenextrapolatingtofuturetokamaks.Generally,it’sbelievedthatitishardtoachieveadeeppenetrationinfuturefusionreactorsbecauseoftheveryhighparametersespeciallyhighelectrontemperatureunderthoseconditions.It’snoteworthythatthedominanteffectsonpelletablationandtheablatantdriftmaytotallydifferfromthoseinexistingdevices,whichalsoindicatesthereasonforthedifferenceofpredictionsmadebydifferentmodelsforfuturereactorswiththesimilarparameters.Figuringoutthephysicsmechanismthatcausesthesedifferenceisthebasistosimulateaccuratelythepelletfuelingprocessinfuturereactors.

Insummary,it’scrucialforthewholedesignoffuturefusionreactorstoaccuratelycalculatethepelletablationrateandpenetrationdepthbasedonadeepunderstandingofpelletfuelingprocessandexploreotherpossiblewaystoincreasethepenetrationdepth.

THEAIMANDEXPECTATIONOFTHERESEARCH:

Inthisstudy,pelletablationrateandpenetrationdepthwillbecalculated,andmethodstoincreasepenetrationdepthwillbeexploredinCFETR.

PelletablationrateandpenetrationdepthinCFETRwillbecalculated.

DTratioofpelletswillbeoptimized.

Pelletablationrateandpenetrationdepthwillbecalculatedinthecaseofencapsulatedpelletswithplasticormetalmaterial.

Othermethodstoincreasethepelletvelocitywillbeexplored.Apossiblewayistoaccelerateapelletwithmicro-wavepowerafterthepelletleavesthecurvedtube.

Transportanalysisafterdepositionofpelletablatedparticleswillbecarriedout,combiningPELLET/PRLwithtransportcodes,suchasTGYRO.

THEEXPERIMENTALMETHODSANDDATAANALYSISMETHODS(whererequired):

ThecalculationresultsofpelletablationrateandpenetrationdepthinCFETRwillbecomparedwiththoseobtainedbyothercodes.Thenthekeyeffectsandparametersdeterminingablationprocesswillbefiguredoutandthecodewillbeimproved.

Inthecaseofencapsulatedpelletswithplasticormetalmaterial,thepelletpenetrationdepthisexpectedtobeincreasedbecauseofahigherpelletvelocityallowedbytheincreasingstrengthofthepellet.Inaddition,shieldingofthepelletwillbeenhancedbyparticlesdepositedbytheshell,whichisbenefitfordeeppenetration.

THEARRAGEMENTOFTHERESEARCHWORK:

Timetable

Date

Activity

2018.09-2018.12

CalculatethepelletablationrateandpenetrationdepthinCFETRandcompareresultswiththoseobtainedbyothercodes.Thenimprovethecodebasedontheanalysisofthepossiblydifferentresults.

2018.12-2019.03

Calculatethepelletpenetrationdepthwithvariedinjectionconfigurations,DTratiosandthematerialsandthicknessofthepelletshellinCFETR.Thenoptimizetheselectionoftheseparameters.

2019.03-2019.07

Exploreotherpossiblemethodstoincreasetheinjectionvelocity.Predicttheevolutionofdensityandtemperatureprofileintheprocessofpelletablationdepositionandperiodbeforeinjectingnextpellet,combiningPELLET/PRLwithparticleandenergytransportcodes.

2019.07-2019.09

FinalReport

THELEVELANDADVANTAGEOFTHEHOSTINGFOREIGNINSTITUTIONONTHISPROJECT:

GeneralAtomicshasoperatedDⅢ-Dformanyyearsandachievedimpressiveandsignificantprogressinthefieldofmagneticconfinementfusionresearch.Onthestudyofpelletfueling,thereareseveralexcellentscientistsinGA.Forexample,L.R.Baylor,PaulParks,JosephMcClenaghan,andWenWuhavedonealotofworkandpublishedmanyhighlevelpapersinthisarea.Parksdevelopedt