Douai, D.

Esser, H. G.

Kreter, Arkadi

Lyssoivan, A.

Möller, S.

Philipps, V.

Samm, U.

Schulz, C.

Sergienko, G.

Team, TEXTOR

Wauters, T.

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Comparative Study of Chemical Methods for Fuel RemovalA. Kreter , S. Möller , C. Schulz , D. Douai , H.G. Esser , A. Lyssoivan , V. Philipps ,U. Samm , G. Sergienko , T. Wauters  and TEXTOR Team1 1 1 2 1 3 11 1 323CEA, IRFM, Association Euratom-CEA, 13108 St Paul lez Durance, FranceLPP-ERM/KMS, Association Euratom-Belgian State, 1000 Brussels, Belgium1Institute for Energy and Climate Research - Plasma Physics, Forschungszentrum Jülich, Association EURATOM-FZJ, TEC, GermanyIntroductionFuel retention in ITER Experimental Removal from castellated structuresInfluence of magnetic fieldTOMAS toroidal plasma deviceAim of the studyGDC in hydrogenFTP/P1-05Optimize the removal efficiency of each methodCharacterize application restrictions of methodsFind alternatives to oxygen as removal gasOptimize removal from remote areas including gapsPropose an integral scheme of fuel removal in carbon containing environmentFigure of merit for cleaning efficiency of GDC and ECR in gapssample positionToroidal vacuum chamber with R = 0.78 m, a = 0.26 m, B ~ 0.1 TRF-assisted DC glow discharge between cylindrical anode and grounded wall as cathode:ECR discharge at 2.45 GHz, P = 1.5 kW,Installation of samples at upper vessel walltp ~ 10 mbar, U = 300 V,  I ~ 1 A, ~ 10 cm s ,  B offp ~ 10 mbar, ~ 10 -10 cm s-2 14 -2 -1-4 15 16 -2 -1GD GD i tiglow anodeECR launchergap side wallpre-coated samplestop surfacee-mail:A.Kreter@fz-juelich.deErosion of top surfaceErosion in upper part of gap, deposition in deeper parts Net source of C from the plasma (vessel walls) Erosion of all surfacesHigher erosion in wider gapEffective erosion yield -carbon atoms per incident ion Higher erosion than in hydrogen, especially top side and gap bottom Removal at 620 K slightly more efficient that 470 KLower yields, but higher removal rateRemoval at 620 K slightly more efficient that 470 KNo significant difference between poloidal and toroidal gapsSignificant erosion in deep regions of gap despite B fieldthan GDC in O (100x higher ion flux!)2 Influence of neutrals deep in gap is crucial for ECRCxHyChemical erosion of carbon:formation of volatile compounds with impinging speciesH + C C HO + C CO,COCo-deposited D/T is released as hydrogen molecule,hydrocarbon or waterRemoval rates are functions ofSurface temperature: According to activation energy ofthe processImpact energy: Enhancement by bombardment withenergetic particles (e.g. ions)Deeper penetrationCreation of active sites for other species (synergisticeffect)x y2Chemical erosion of carbon by hydrogen and oxygenTechniques for fuel removal and vessel wall conditioningHCarbonOCarbonCCOO2GDC in oxygenECR in oxygenH GDC 470 K2 H GDC 620 K2O GDC 470 K2Effective erosion yield -carbon atoms per incident ionO GDC 620 K2O ECR poloidal 620 K2O ECR poloidal 470 K2 SummaryWCFC2.5 mm1 mmBottomDistance to upper edge [mm]0 1 2 3 4 5 6 7 8 9 10Top side-7-6-5-4-3-2-10-8Layer thickness change [nm/h]0-20-40-60-80-100-120-140-160-180-7-6-5-4-3-2-10-8Distance to upper edge [mm]0 1 2 3 4 5 6 7 8 9 10Layer thickness change [nm/h]0-20-40-60-80-100-120-140Top sideBottom2.5 mm1 mmDistance to upper edge [mm]0 1 2 3 4 5 6 7 8 9 10Distance to upper edge [mm]0 1 2 3 4 5 6 7 8 9 10-0.35-0.30-0.25-0.20-0.15-0.10-0.050.000.05-0.50-0.45-0.40Layer thickness change [nm/h]0-100-200-300-400-500-600-700Layer thickness change [nm/h]0-100-200-300-400-500-600-700-0.35-0.30-0.25-0.20-0.15-0.10-0.050.000.05-0.50-0.45-0.40Gap side wallGap side wallGap side wall Gap side wall1 mmBottom2.5 mm1 mmBottom2.5 mmTop sideTop sideDistance to upper edge [mm]Layer thickness change [nm/h]-0.35-0.30-0.25-0.20-0.15-0.10-0.050.000.050.100 1 2 3 4 5 6 7 8 9 10-35-30-25-20-15-10-50510Gap side wallTop side-0.35-0.30-0.25-0.20-0.15-0.10-0.050.000.050.10Layer thickness change [nm/h]-30-25-20-15-10-50510Distance to upper edge [mm]0 1 2 3 4 5 6 7 8 9 101 mm(2.5 mm n.a.)Gap side wallTop sideBottom2.5 mmBottom1 mmEffective erosion yield -carbon atoms per incident ionEffective erosion yield -carbon atoms per incident ionEffective erosion yield -carbon atoms per incident ionp = 9 10 mbar, = 2.4 10 cm s , duration 9h 57min  -3 14 -2 -1i p = 9 10 mbar, = 2.2 10 cm s , duration 3h 28min  -3 14 -2 -1ip = 9 10 mbar, = 4.2 10 cm s , duration 33 min  -3 13 -2 -1i p = 9 10 mbar, = 4.8 10 cm s , duration 27 min  -3 13 -2 -1ip = 10 mbar, n = 1.2 10 cm , T = 2.8 eV, sheath potential 15 eV, = 3 10 cm s-4 11 -3 15 -2 -1e e i  duration 385 s duration 573 sTypical deposition rates in a tokamak discharge:2 3 nm/s at top surface and upper edge of gap and 0.5 nm/s on gap bottom1000 nm depositionMeasured removal rates at 350 C and 1 mm gap:– at top surface and at upper edge of gap and200 nm on gap bottom within one ITER pulse of 400 s: 35 nm/h at top surface, 20 nm/h at upper edge and 2 nm/h on gap bottom: 170 nm/h at top surface, 30 nm/h at upper edge and 70 nm/h on gap bottom: 600 nm/h at top surface and at upper edge and 150 nm/h on gap bottomhydrogen-GDC100 hours to remove the layer from gap bottom deposited within one ITER pulseoxygen-GDC30 hours to remove the layer deposited within one ITER pulseoxygen-ECR 1.5 2 hours to remove the layer deposited within one ITER pulse–oxygen-TCR for layer of 3 m removal rate is higher than ECR : 50 nm/h at 200 nm, uniformlyremoval rate is proportional to layer thickness:Start cleaning of thick layers ~10-100 m by oxygen-TCR for ~24 hoursContinue cleaning of remaining layer by oxygen-ICWC and / or oxygen-GDC for ~10 hoursThick layer can be removed within one weekendProposed combined removal scenario, applied once a weekProjection for ITERgapbottomgapside walltopsurface1 cm1 cm1 cmEroded carbon atoms per unittop surface area and time [cms]-2-11.0 1015Top surfaceGap 1 mmGap 2.5 mmH -GDC470 K2 H -GDC620 K2 O -GDC470 K2 O -GDC620 K2 O -ECR470 K2 O -ECR620 K200.8 10150.6 10150.4 10150.2 10151.2 10151.4 10151.6 10151.8 10153.5 10154.0 10154.5 1015Erosion from gapsis normalized togap entrance areaHigher normalizedremoval rates for gapsthan for top surfaceNormalized removal ratesare similar for 1 and 2.5mm gaps~~Reactive species areused more efficiently ingaps (multiple collisionswith walls)Integral removalefficiency is proportionalto gap widthEffective erosion yield -carbon atoms per incident ionWall materials, i.e. carbon, are eroded and transported byplasmaMaterials accumulate in remote areasCo-deposition of tritium, i.e. in a-C:T layersGaps are additional remote areas, distributed allover the vesselTotal area of gaps in ITER ~1000 m2 Fuel removal techniques need to be developed andoptimized, i.e. for gap cleaningApplication of heat loadsDesorb tritium from thesurface or to ablate re-deposited layersDisruption cleaningPhotonic cleaning by flashlamps and lasersExchange of hydrogen isotopesBring non-radioactive hydrogenisotopes in contact with the tritiumcontaining surfaceGasConditioning plasma dischargein the form of:PhysicaldesorptionIon-induceddesorptionConditioningplasmadischargeChemical etching		Based on the chemical reactivity of the removal gases towards the hydrogen isotopesand the wall materials as carbonActivation energy is provided by:Active wall heatingThermo-Chemical Removal (TCR), also known as baking in reactive gasesEnergetic incident particlesConditioning plasma discharge: GDC, ICWC, ECWCStudies in Forschungszentrum Jülich have been concentrated in recent years onchemical methods includingThermo-Chemical Removal (TCR) Glow-Discharge Conditioning (GDC)Ion-Cyclotron Wall Conditioning (ICWC) erosion zonedeposition zoneup to ~10 mLimiter tile from TEXTOR after one campaignLaboratory device PADOS13,56MHz+ Self-biasGrounded AnodePADOSchamberSamplesGas inletPressuresensorsPumpsGrounded heating plateCeramicFloating cageUsed for coating of samples by amorphous deuterated layers a-C:D and for TCRCapacitive RF discharge between two circular electrodes, 25 cm, distance 7 cmOption of biasing for lower electrodeLower plate is heatable, e.g. for TCRa-C:D layers are produced by Plasma Enhanced Chemical Vapour Deposition (PECVD) inmethaneTokamak TEXTOR equipped with ICRF antennaeR = 175 cm, a = 46 cmCircular plasma cross-sectionAll limiters made of carbonTest limiter locks to expose samplesFrequency 25 - 38 MHzTypical ICWC power 2 x 50 kWOperational at B = 0.2-2.5 TtExamples of a-C:D coated samplesTCR and ICWC are compatible with highmagnetic field, GDC is notGDC can be operated at B field of up to ~3 mTGDC is compatible with residual fields fromferritic inserts planned for ITER to reduce Bfield ripple0 2 4 6 8 10 12 14020406080100B [mT]tat anode positionLocal GDC wall current [A] 90 from anode180 from anodeToroidal symmetry of GDCin presence of low B fieldp = 0.3 barU = 180 VheliumDCThermo-chemical removal (TCR)~~Compatible with gap geometryTCR in oxygen isTCR in oxygen requires elevated wall temperature of >300 C, Arrhenius-type temperaturedependenceRemoval is homogeneous in the entire layer due to its porosityat 350 C at least one order of magnitude more efficient than in ammoniaTCR in ammonia caused delamination of layerPotential source of dustCan by utilized for first mirror cleaning in ITER Removal rate is proportional to inventoryDeuterium is boundto the pore wallsMost deuterium isreleased, gases canremain in the closedporesTCRThe pore networkhas open andclosed pores whichare not accesibleadditional pores attachto the network, densitydecreasesTCRSurface Surface Surface SurfaceTCR: mechanism of deuterium removal TCR: mechanism of carbon removalRemovalmethodCompatibilitywithB fieldMinimumrequired walltemperatureHomogeneity ofremovalD removalrate[at./m2h]C removalrate[nm/h]TCR (baking) Yes 300CHigh, also forremote areas31021(for 200 nm)50(for 200 nm)GDC OK for <3 mTRoomtemperatureHigh for plasma-wetted areas,limited for remoteareas71021 170ICWC/ECWC YesRoomtemperatureLimited on a part ofplasma-wetted area201021 600Removal rates are given for oxygen at wall temperature of 350 CBiased cathode28 cm35 cmForschungszentrum Jülich  |  Institute of Energy and Climate Research - Plasma Physics  | Association EURATOM - FZJ

Comparative Study of Chemical Methods for Fuel Remova

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Comparative Study of Chemical Methods for Fuel Remova

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