Experimental tests of lisn alloys as potential liquid metal for the divertor target in a fusion reactor

Experimental tests of LiSn alloys as potential liquid metal for the divertor target in a fusion reactor ARTICLE IN PRESS JID NME [m5G; December 24, 2016;21 45 ] Nuclear Materials and Energy 0 0 0 (201[.]

ContentslistsavailableatScienceDirect

Nuclear Materials and Energy

journalhomepage:www.elsevier.com/locate/nme

Experimental tests of LiSn alloys as potential liquid metal for the

divertor target in a fusion reactor

F.L Tabarés∗, E Oyarzabal, A.B Martin-Rojo, D Tafalla, A de Castro, F Medina,

M.A Ochando, B Zurro, K McCarthy, the TJ-II Team

Fusion National Laboratory CIEMAT, Av Complutense 40, Madrid 28040, Spain

a r t i c l e i n f o

Article history:

Received 11 July 2016

Revised 21 October 2016

Accepted 26 November 2016

Available online xxx

Keywords:

Plasma facing Materials

Liquid metals

LiSn alloys

Hydrogen retention

Reactor materials

a b s t r a c t

ThefirstexperimentsofexposureofaLiSnalloy(Li/Snatomicratio=20/80)toahydrogenplasmain TJ-IIareherepresented.Solidandliquidsampleshavebeeninsertedattheedgeandevidenceofsample meltingofasolidsampleduringplasmaexposurehasbeenobserved.Anegligibleperturbationofthe plasmahasbeenrecorded,evenwhenstellaratorplasmas areparticularlysensitive tohighZelements duetothetendencytocentralimpurityaccumulation.Meltingofthesamplebytheplasmathermalload didnotleadtoanydeleteriouseffectontheplasmaperformance.Stronglithiumemissionwasdetected

atthe LiSnsamplebutnosign ofSn contamination and low values ofZeff and radiated power were deduced.Hydrogenrecyclingwasstudiedattwodifferenttemperaturesandnochangewasdetectedin therangeof300–750K.TheretentionofH2bythealloywasaddressedinseparateexperimentsatthe laboratory.Valuesintheorderof0.01%H/(Sn+Li)werededucedinagreementwithinsituTDSanalysis

oftheplasmaexposedsamplesandpreviousreports

© 2016PublishedbyElsevierLtd ThisisanopenaccessarticleundertheCCBY-NC-NDlicense (http://creativecommons.org/licenses/by-nc-nd/4.0/)

1 Introduction

Amongthepossibleliquidmetals(LM)presentlyconsidered as

candidates for the development ofan alternative solution to the

Power Exhaust Handling in a future Fusion Reactor (Li, Sn, Ga),

tin lithiumalloysoffer uniquepropertiesintermsofevaporation,

fuel retention and plasma compatibility This is the reason why

thisparticularLM waschosen asmaincandidateinthe USAPEX

project [1] Although the sputtering andevaporation

characteris-tics were tested atthe laboratory level,confirming the

preferen-tialsputteringandevaporationoftheLicomponentinthemolten

phase, no hot plasma testingwas ever performed For the same

temperature, similar values of Li sputtering yield by D ions was

found forliquid LiandliquidLiSn alloys, witha basically

identi-cal ioncomposition ofthe sputteredLi[2] However, evaporation

rates from thealloy are up to a factor of 1000lower than from

thepureLimetal.Veryrecently,aLiSn(30:70at.%)alloyhasbeen

exposed to ISTTOK tokamak andvery promising resultson D

re-tentionandsurfacesegregationofLiwereobtained[3] Motivated

bytheseresultsafullcampaignofLiSntestinginTJ-IIplasmashas

beeninitiated.Inadditiontothesehotplasmatests,laboratory

ex-∗ Corresponding author

E-mail address: tabares@ciemat.es (F.L Tabarés)

perimentaimed atevaluating the H retentioncharacteristics and the secondary electron emission of LiSn surfaces atseveral tem-peratureswere undertaken.Also,insitudesorption ofDafter ex-posuretoTJ-IIplasmaswascarriedout

Inthiswork,anaccountoftheresultsobtainedandtheir impli-cationsfortheuseofLiSnalloysasdivertormaterialsolutionfora futureFusionReactorisgiven

2 Experimental set-up

2.1 Sample preparation

For the experiments reported here, a commercially available LiSn alloy (Princeton Sci Corp., Easton, PA, USA) with a Li: Sn atomicratioof20:80wasused

DuetothepresenceofseveraleutecticsintheLiSnphase dia-gram[4] ,achievingahomogeneousliquidphasebydirectmelting

ofthe LiSnsamplemaybe challenging Formation ofslagon top

of the molten phase is commonly observed, thus preventing the productionofaclean,singleliquidentity.Itwasfoundthatstrong stirringduringthefirsttimethealloyismelteddowninanoven wasmandatoryinordertogetahomogeneousliquidphase.Once thisisachieved,coolingdowntothesolidphaseagainproducesa smooth,clean surfaceandno furtherstirring isneededanymore http://dx.doi.org/10.1016/j.nme.2016.11.026

2352-1791/© 2016 Published by Elsevier Ltd This is an open access article under the CC BY-NC-ND license ( http://creativecommons.org/licenses/by-nc-nd/4.0/ )

Pleasecitethisarticleas:F.L.Tabarésetal.,ExperimentaltestsofLiSnalloysaspotentialliquidmetalforthedivertortargetinafusion

0 100 200 300 400 500 600

0.00E+00

2.00E-09

4.00E-09

6.00E-09

8.00E-09

1.00E-08

1.20E-08

1.40E-08

1.60E-08

1.80E-08

2.00E-08

Time (s)

Abs 0,35 Torr Abs 1 Torr Abs 3,5 Torr Temperature

Fig 1 TDS spectra of hydrogen desorption from a LiSn alloy (20:80) exposed to

several pressures of H 2 at 425 °C The peak at ∼200 °C correponds the decomposi-

tion of lithium hydroxide

Thisprocedurewasessentialwhenaddressingtheimpregnationof

ametallicmeshwiththeliquidalloy

2.2 Set-ups

Twokinds ofset-upwere useddependingonthe experiment:

avacuumchamberforlaboratoryretentionexperimentsanda

ma-nipulatorsystemwithavacuumlockforexposuresinTJ-II,as

de-scribedinthefollowingparagraphs

For the absorption experiments (Fig 1 ), the oven is charged

withsolid LiSn Prior to the absorption experiments, the sample

isheated up to 550°C forconditioning purposes Oncethe

sam-plehasbeenoutgassedandcooled down,itisheatedagainupto

thedesiredtemperature andthevalve to the pumpingsystem is

closed.Afterthat,thechamberisfilledtotherequiredpressureof

H2 (0.35, 1 and3.50Torr respectively) by expansion froma

pre-filledreservoiratpressures 100× higherthan thoserequired (35,

100and350Torrrespectively)

3 Results

3.1 Laboratory studies

Inprinciple,thequantity ofabsorbedHafteragiventimecan

besimplyevaluatedfromtheresultingpressuredropinthesealed

experimentalchamber.However, dueto thelow valuesof

hydro-genretention in LiSn the change inpressure duringthe

absorp-tionto monitor the absorbedquantity is not accurate enough in

the present set up as to obtain any reliable absorption results

ThereforeonlytheresultsregardingtheThermalDesorption

Spec-troscopy(TDS)measurements afterexposureto H2 atto different

temperaturesandpressures willbeshowninthissection.The

ab-sorptionexperimentsareonlycarriedoutinordertoreachthe

hy-drogenequilibriummolefractionintheLiSnforthedifferent

con-ditions.Theabsorptiontime islongenoughastoachieve

absorp-tionequilibriumin theLiSn foreach condition, thisis confirmed

byrepeatingtheabsorptioninoneconditionfortwodifferent

ab-sorptiontimesandcorroboratingthatthedesorbedquantityinthe

TDSis the same for both cases We use absorption times of 1h

thoughwe haveobservedthat theequilibriumisalreadyreached

after15mininallconditionsheretested

Fig 1 shows the results of the TDS for the case of

absorp-tionat425°Cforthreedifferentabsorptionpressures(0,35,1and

3,5Torr) forthe calibrated pure hydrogen signal at amu=2, and

with the background subtracted Because of the small values of

absorption (therefore desorption) in LiSn the background signal

Fig 2 Siebert’s plot of the solubility of H in LiSn (20:80) Data from the present

work at several temperatures are shown together with previous measurements at different Li: Sn ratios and the fitting there displayed ( Ref [5 ])

duetothedesorption overtime ofthechamberwalls(which are slowlyheatedduringtheTDS)isnotnegligiblewithrespecttothe desorbed quantity and must be subtracted from the rawdata of the Quadrupole Mass Spectrometer (QMS) As expected the des-orbed quantity increases forincreasing absorption pressure indi-catingthatthesolubilitylimit(i.e.,onsetofhydrideformation)has notbeenreachedinthestudiedpressurerangeatthestudied tem-perature,ifthiswasthecasethedesorbedamountaftersaturation shouldremainconstant,andapeakathighertemperatures, corre-spondingto theHLi decomposition,should be observed.This be-haviourwasexpectedbasedonpreviousliteraturedata[5] ,which showshydride formationpressures over 7000Torrforother mix-turesofLiSn.Thecomparisonwiththeseresults,showninFig 2 ,

isdiscussed inmore detaillater The TDSforthethree pressures presentsdesorptionpeaksatsimilardesorptiontemperatures,one

ortwo(itisnotclear)atlowtemperatures(probablyrelatedwith hydroxide desorption) anda second peak at around 400–500°C This second peak agrees well with the desorption peak of pure lithium observed in previous experiments [6] Even though only theresultsforabsorption at425°Careshownforclaritythe TDS forthetwo otherstudiedtemperaturespresentsdesorptionpeaks

atsimilar temperaturesandthe sameevolutionwiththe absorp-tionpressure

3.2 Plasma exposure in TJ-II

Several methods of exposing LiSn to the hot plasmas of TJ-II [7] were tested Only ECR heated plasmas (600kW, 53GHz, 2nd harmonic) were used in thesetests The main limiter was a CPS LiquidLithiumsystemkeptatT>200°Cinallcases,andthefirst wallwascoveredbyalithiumlayer.Thebasicsetupusedforthe insertion of LiSn samplesinto the plasmaedge wasthe sameas thatpreviouslyusedforlithiumexposures[8] Threedifferent sam-pleswere used:asolid pieceofLiSn,ameshofMopartially em-beddedinmoltenLiSn,aSSmeshfullyembeddedinmoltenLiSn andadirectdepositionofthealloyontheSSbarmadebydipping the“finger” intothemoltenalloy.The temperatureofthe“finger” wasvaried in the SSmesh caseanda thermocouple attachedto thebasewasusedforitsmonitoring.Inthisway,thecomparative behaviour of solid andliquid LiSn(melting temperature=330°C) couldbeaddressed

Fig 3 showsthetracesofthemainplasmaparameters for se-lected shots, summarized inTable 1 They includeshots without bar insertion (#41562,at −4cm) andwith insertion atthe LCFS butattwodifferentinitialtemperaturesoftheLiSnalloy(#41569

at120°Cand#41573at440°C).Fortheexamplesshownhere,

2

4

6

8

#41562

ne(10 12

cm -3 )

H Lim

H puffing ECE central Bolometer center SRX center

time (ms)

0 2 4 6 8

#41569

time (ms)

0 2 4 6 8

# 41573

time (ms)

Fig 3 Traces of the main plasma parameters for the reference shots used in this work and summarized in Table 1 Line average electron density, H αat the main limiter,

H αcorresponding to the gas fuelling, central ECE signal (Te), central integrated bolometer (total radiation) and Soft X ray signals are displayed

Summary of plasma conditions for reference shots

Shot # Finger location LiSn T ( °C) Electron density

(10 13 cm −3 ) Te (a) eV

talradiationvalues,aswellasSoftXRayemission,werevery

sim-ilartothoseobservedwhenapurelithiumsamplewasexposedto

theplasmainTJ-II,withtotalradiationpowersbelow10kW.Fig 4

shows the value of the densitynormalized total radiation (from

bolometry),andinFig 5 ,thereconstructedvaluesofZeff are

dis-played Valuesbelow1.5weregenerallyobtainedalthoughatime

increase ofthis parameter,up to 1.8, canbe seen forthecase of

hotfingerinsertion.Thisbehaviourcanbeascribedtothe

progres-siveincrease oftheevaporatedLiflowasthesampleisheatedby

the plasma.A search forcharacteristicSnIandSnII linesinthe

visible, aswell as SnIII andSnIV lines inthe VUV (50–80nm),

did notyield evidence ofthepresence oftin in theplasmaeven

forthemostpotentiallyperturbingconditions

Fig 6 showssomerepresentativetracesofLi,Li+andHα

emis-sions As seen, Lirelated signals show a fast increase with time

whilethe Hα signal remains fairlyconstant Inorderto getsome

insightintotherecyclingpropertiesofthealloy,thelocalHαsignal recordedinfrontofthefingerisnormalizedtotheHαsignalfrom themainCPS Lilimiter, keptatconstant temperatureall through the experiment The results for several initial temperatures and plasmaflowsaredisplayedinFig 7 Whileinshots#68and69the LiSnsamplewasheatedonlybytheplasma,in#72and73 itwas intentionally heatedexternally at440°C beforeplasma exposure However,thereisnodifferenceinthetime evolutionofthe recy-clingcharacteristics,sincetheplasmafluxesaresimilar.Forlower plasmadensities(fluxes),aprogressiveincreaseofthelocal/global

Hα signaltakesplaceat440°C,finally reachingthesamevalueas thoseathigherdensities.Thistypeofincreaseisnotseenforthe lowdensity/lowTsample,however

WhenLiSn wasdirectlyapplied to abare SSbar, i.e., withno meshstructureinbetween,asystematiccollapseoftheplasma af-ter a few tens of milliseconds was seen Due to the characteris-ticsof microwaveabsorption by theplasma, ECRH becomes inef-ficientatdensitiesabove thecut-off limit(lineaveragedensityof

∼1×1019m−3 inTJ-II).Thislimitingdensitywasquicklyachieved

inthereferreddischarges;thus,precludingapossibleanalysisofa potentialradiativecollapsebymassiveimpurityinjection, as indi-catedbyspectroscopicdata.Althoughthereasonofsuchbehaviour

isnot understood,andnovisual accesstothe samplewas possi-bleduringthemachineoperation,onemayspeculateaboutafast meltingofthealloyby theplasmaloadfollowedby drippinginto

5

10

15

20

25

30

1080 1100 1120 1140 1160 1180 1200 1220

P rad /n

e kW/10 12 cm -3

P/ne 41562

P/ne 41569

P/ne 41573

time (ms)

Fig 4 Total radiation normalized to the average density for the three shots dis-

played in Table 1

1

1.2

1.4

1.6

1.8

2

1080 1100 1120 1140 1160 1180 1200 1220

Zeff

41562

41569

41573

time (ms)

Fig 5 Time evolution of Zeff during the three reference shots deduced from soft X

ray emission (SXR) traces

the vacuum chamber or receding from the plasma-wetted area,

thuseventuallyleavingabareSSsurfaceexposedtotheplasma

Finally, the full particlebalance duringthe operation daywas

analysed.ThetotalH2 fuelledduringthedaywasestimatedfrom

thecalibratedpuffingsignalwhilethedesorbedamountaftereach

dischargewasrecordedbymassspectrometryandthenintegrated

over the 50 shots produced An average recycling coefficient of

R=0.1 wasdeduced in this way, starting atlower values at the

beginning of the day The CPS finger was outgassed in a

sepa-rate chamber without exposing it to the air Even so, traces of

water,CO/N2 and CO2 were recorded duringthe TDS, as seen in

Fig 8 While the total amount of missing H was estimated in

6×1021atoms,integrationofthemass2recoveredduringtheTDS

yieldedonly6,2×1019Hatoms.DuetothesmallamountofH

re-coveredandthecontributionofmass2byothermolecules,manly

water,present athigher concentrations,the direct ratio between

thedesorbedhydrogenandthat retainedinallthe plasmafacing

components, such as first wall and main limiter, of 1% must be

consideredonlyasa maximumvalue.Fora massofthe

interact-0 2 4 6 8 10

Li and H emission

Li I emission

Li I emission

Li II emission

H emission

time (ms)

Fig 6 Example of the time evolution of some characteristic emission lines dur-

ing the plasma shot LiI (671 nm), LiII (538 nm) ad H α(656 nm) Two examples

of Li emission corresponding to solid (cold) and liquid (hot) LiSn initial state are shown, although their absolute magnitudes cannot be compared as they correspond

to different locations in the plasma periphery The strong rise of the corresponding lithium signals indicates heating of the sample by the plasma Note their negligi- ble value at the beginning of the shot, indicating evaporation-dominated ejection

of the Li atoms A delay in the emission of Li from the cold finger of ∼60–80 ms is apparent in the figure

0 1 2 3

Recycling

H 4/H C4 41568

H 4/H C4 41569

H 4/H C4 41571

H 4/H C4 41572

time (ms)

Cold sample Sample at 440 C

Fig 7 Normalized local H αsignals (from the LiSn finger) to the total plasma flux (H αfrom the main limiter) for two different initial temperatures and different plasma densities Note the same recycling characteristics for the cold and hot cases

at similar densities

ingalloyarea of1g,thisretentionimpliesH/(LiSn)atomratiosof

<1%

4 Discussion

4.1 Laboratory retention experiments

InordertoobtaintheequilibriumHmolefraction(XH)ateach studied condition from the TDS results, the integral of the cali-brated PH2 vs time foreach caseis first evaluated andthen

di-10 -9

10 -8

10 -7

10 -6

10 -5

0.0001

250 300 350 400 450 500 550 600

TDS Sn-Li (all species)

amu 2

amu 18

amu 28

amu 32

amu 44

T, ºC

t, s

Fig 8 TDS of the LiSn finger after exposure to 50 plasma shots A significant con-

tribution to mass 2 (H 2 ) can be ascribed to cracking of water in the ionization

chamber of the QMS

videdby the totalamount ofexposed Li20Sn80(in all cases0,12

mol) Fig 2 shows the comparison of the results of H

equilib-riummolefraction(XH)ofthepresentexperimentsandtheresults

fromprevious literature data[4] The resultsin theliterature are

for higher temperatures and higher exposure pressures than the

presentstudybuttheyshowa linearrelationbetweenthesquare

rootoftheequilibriumpressureandtheequilibriumHmole

frac-tion (Sieberts’ law) for the two mixtures under study(Li57Sn43

and Li62Sn38).This linear relationcan be used to compare with

thepresentresults

As it can be observed,the results in the presentwork are in

goodagreementwiththelinefittedtotheresultsobtainedinthe

literature data.Inour casethereissome effectof theabsorption

temperature onthe slope ofthe line,indicating lower H

equilib-riumconcentration forlowertemperatureswhile intheliterature

noremarkablechangeswithtemperaturearereported.Ithastobe

takenintoaccountthatthetemperaturerangeintheirexperiments

ishigher(from525to800°C)

Forthecaseof1Torr(133Pa)exposure(theapproximate

pres-sureexpectedina reactordivertor) the equilibriumH

concentra-tionisbelow1.10−4 forthethreetemperaturesstudied.These

val-ues aremore thantwo orders ofmagnitudesmaller thanforthe

case of pure lithium Also, in the LiSn case, no hydride

forma-tion takesplace atthe relevant divertor pressures and

tempera-tures, while for the case of pure lithium a certain temperature

(above∼ 500°C)wouldbeneededinordertoavoidtheformation

of LiH.It should also benoted that theresulting Huptakes here

found are in good agreementwith those obtainedin hot plasma

experiments for the same alloy [3] thus suggesting that no

sig-nificant difference between plasma and gas exposure behaviour

exists

4.2 TJ-II exposure

TheresultsobtainedinTJ-II,partiallydisplayedinFigs 3–7 ,

in-dicate good compatibilityofthe LiSnalloyheld in amesh

struc-ture (CPSarrangements) withhot stellarator plasmas.No

signifi-cant increase ofplasmacontaminationleading toenhanced

radi-ation orfuel dilutionhas beenseen Theobserved behaviour fits

wellintothepicturepreviouslyobtainedfromlaboratorydata.The

strong enrichmentofthesurfaceof thealloybylithium

segrega-tionmakesitindistinguishablefrompurelithiummetal.However,

andcontrarytowhathasbeenpreviouslypostulated[2] ,no melt-ing of the alloy may be required in order to produce a Li rich surface according to our data However, in situ surface analysis

of the alloy “as prepared” would be required in order to deter-minewhetherLisurfacesegregationtakesplaceduetothecooling method(inertial)usedduringitspreparationorbyplasmainduced effects

AlthoughLi emission from the cold samples seems to be de-layedby50–80msrespecttothehotfingercase,asseeninFig 6 , one would expect to see Sn emission by sputtering in the ab-senceofsurfacesegregationforsolidLiSnsamples.Thisisnotthe case,evenwhenLCFSelectronictemperaturesintherangeof50eV arecommonlyrecordedbytheHebeamdiagnosticandLangmuir probes Moreover, local recycling wasseen to be independent of theinitialtemperature(physicalstate)ofthealloy,asdisplayedin Fig 7 Thefactthatplasmaswithhigherdensitiesachieveahigher, slowlyincreasing recycling value within the duration ofthe shot mayindicatetheachievementoftheHequilibriumconcentration

onthesampleduringthedischarge.Forthetypicaledge parame-ters,withdensitiesattheLCFSof∼1×1012cm−3,particlefluxesof

∼1018cm−2 −1 aretobeexpected.Foranexposureareaof3cm2,

aconcentrationof0.1%H/LiSnwillbeachievedin<2 whileonly 0.2 (typicaldischargeduration)willberequiredforthevaluesof 0.01%found in the laboratory tests However, as the emission of

Hα fromthefingerwasnot systematicallyrecordedfromthe be-ginningoftheexposuretotheplasma,thedatapresentlyavailable

donotallowforareliableassessmentofthisimportantparameter andmoreexperimentswillberequired

Although no direct recording of the surface sample tempera-tureduringtheshotswasmade, thetimeevolution oftheLi sig-nals indicate that evaporationrather than erosionby the plasma (basicallyconstant forthe edgecharacteristics ofthepresent dis-charges) dominate its intensity Assuming a temperature depen-dence of Li evaporation from the alloy identical to that of pure

Li(but withabsolutevaluesmuchsmaller) afirstestimate ofthe temperatureexcursionsofthesamplesurfacecanbemade TheevaporationfluxofaLisamplecanbeexpressedas[9] :

whereAisaproportionalityfactorandPvap=C.10(18.4-18,750/T).For pureLi, ifPvap isexpressedinPa,C=133.3,whileforLiSnalloys,

afactor of∼1000reduction inPvap hasbeenpreviously reported [10]

ForfullionizationofLiintotheedgeplasmas,thephotonflux,

ILi isproportionaltotheincomingfluxfromthesample Thisflux willevolveintimeasthetemperatureofthefingerrisesduetothe plasmaload Assumingasemi-infiniteslabmodelforthethermal responseofthefinger,onehas:

whereQisthethermalload(Wm−2),kthethermalconductivityof thesurface, p thespecificheat ofthealloyandρits density.By substitutingTinEq (1) by theexpectedsquareroottime depen-dencegivenby Eq (2) ,thenfittingthelnILi(t)vs.t curve,avalue

ofthe“thermalparameter” 2Q /

πk pρcanbeobtained.Example

ofthiskindoffittingfortwoinitialtemperaturesofthefinger,400 and730K,are showninFig 9 Asseen,averygoodfittingtothe expectedbehaviour is obtained by usinga common value of the thermalparameterof22 −1/2forbothcases.However, ifthe tab-ulatedvalues ofk,c p andρ fora LiSnmixture are assumed[10] , valuesofQupto4timeshigherthanthosededucedfromthe ex-perimental edge parameters [11] are obtained This would be in linewithastronglyreducedthermalconductivity, k,ofthe dam-aged (corroded) SS CPS, visually observed after the experiments

a) b)

-6

-4

-2

0

2

1080 1100 1120 1140 1160 1180 1200 1220

Fitting T(t)=730+22.sqrt( t)

ln I(Li)

Fitting T(t)=400+22.sqrt( t)

ln I(Li)

time

Fig 9 Fitting of the lithium signal to the behaviour predicted by Eqs (1) and ( 2 ) Left: initial temperature 730 K Right Initial temperature 400 K Note the different time scales in both plots

Directtemperaturerecordingsbyopticalpyrometerandtheuseof

WorMomeshesarenowforeseentoaddressthisimportantissue

5 Summary and conclusions

First testsofcompatibilityofa Li/Snalloywithstellarator,hot

plasmashavebeenperformedinTJ-II.Inaddition,complementary

laboratory experiments of H retention by the alloy were carried

outatseveraltemperaturesandgaspressures

Theresultsobtainedaresummarizedbelow:

- Hretentionvaluesof∼0.01%H/(Sn+Li)atT<450°Cwere

de-ducedfromTDSatthelaboratory(gasexposure)

- AgreementwithpreviousreportsandinsituTDSinTJ-II

- InsertionofaLiSn sampleinto theedgeofTJ-IIdoesnotlead

anysignificant perturbation of plasmaparameters Zeff values

typically below1.5 and very low Prad/Pinvalues (<2%) were

deducedevenwithhotsamplesattheLCFS

- Conversely,plasmaoperationbecameimpossibleiftheSS

sup-port(finger)isuncovered

- OnlyLiemission wasdetected No tracesofSnwere detected

byvisibleandUVspectroscopy

- Hrecyclingdidnotevolvewithtemperature

- PoorthermalconductivityoftheCPSofLiSnwasdeducedfora

damagedSSmesh

TheseresultsprovidegoodperspectivesforuseofLiSnalloysas

aPFCinaReactor

Acknowledgements

This work has been carried out within the framework of the EUROfusion Consortium, WP PFC, and hasreceived fundingfrom theEuratom research and training program 2014–2018undergrant agreement No 633053 The viewsand opinions expressed herein

donotnecessarilyreflectthoseoftheEuropeanCommission.

References

[1] M.A Abdou , et al , On the exploration of innovative concepts for fusion cham- ber technology, Fusion Eng Des 54 (2001) 181–247

[2] J.P Allain , et al , J Nucl Mater 290–293 (2001) 33 [3] J Loureiro et al Proc ISLA-4 Conference Granada Sept 2015 (to appear in Fu- sion Eng Des.) Also in this Conference

[4] C John Wen , R.A Huggins , Thermodynamic study of the lithium-tin system, J Electrochem Soc 128 (1981) 1181

[5] R Schumacher , A Weiss ,H solubility in the liquid alloys lithium-indium, lithi- um-led and lithium-tin, Ver Bunsenges Phys Chem 94 (1990) 648

[6] F.L Tabarés , et al , Studies of plasma-lithium interactions in TJ-II, in: Proc IAEA Conference, San Diego CA, 2012 P5/36

[7] F.L Tabarés , et al , Effect of Li coating in plasma confinement and performance

in TJ-II, Plasma Phys Control Fusion 50 (2008) 124051 [8] F.L Tabarés , et al , Testing the compatibility of lithium elements with a hot plasma: studies of solid lithium insertion in TJ-II, Proc 39th EPS Conf Stock- holm, 2012

[9] A.F Mills , Heat Transfer, second ed., Prentice Hall, Inc., Upper Saddle River, New Jersey, 1999

[10] S Sharafat , N Ghoniem , Summary of Thermo-Physical Properties of Sn and Compounds of Sn–H, Sn–O, Sn–C, Sn–Li, Sn–Si and Comparison of Proper- ties of Sn, Sn–Li, Li, University of California, 20 0 0 Pb–Li Technical Report UCLA-UCMEP-00-31

[11] F.L Tabarés , et al , First liquid lithium limiter biasing experiments in the TJ-II stellarator, J Nucl Mater 463 (2015) 1142