Tokamak NOVA-UNICAMP Reent Results
A.M. Daltrini,M. Mahida, M.J.R. Monteiro, and C. O. Kaminishikawahara
InstitutodeFsia\GlebWataghin", UniversidadeEstadualde Campinas,
C.P.6165,13083-970, Campinas,SP,Brazil
Reeivedon26June,2001
TokamakNOVA-UNICAMPisa smalltokamakwith ironore andonduting shellstabilization
builtto studyplasma-wall interationandoptialdiagnosti development. Charateristiplasma
behavior was the appearane of 2-3 kHz spike osillation during entire disharge with very high
X-rayativity whihprevent ouroptial diagnosti development. By modifying apaitane and
hargingvoltageonOHandvertialeldbanks,inordertoobtainsimilardishargeurrentshape,
mostof2-3 kHzspikeshasbeentakenout,althoughsome ativitiesstill remainstobeanalyzed.
Nevertheless, the high X-ray ativity whih jeopardize our optial measurements is ompletely
eliminatedand timevaryingparameteras ion temperature isnowpossible to befollowed during
wholedisharge.
I Introdution
The NOVA-UNICAMP tokamak, former NOVA II
tokamak [1℄ from Kyoto University-Japan, is a small
mahine operating at our Laboratory sine 1996. Its
mainharateristisare: majorradiusof30m,minor
radius of 6 m, plasma urrent of 10 kA, plasma
dis-harge timeof 15ms, andtoroidal magnetield of 1
T.Otherharateristisanbefoundin[2℄.
Inourreentpubliation[3℄wehavepointedoutthe
progress in spetrosopy researh, showing also some
tokamakresultsaspeakedosillationsobservedin
spe-tralemissionsandloopvoltagesignals.
Wepresentnowthe results in new mode tokamak
disharges and the new diagnostis after some
modi-ations in tokamak parameters and improvement in
someother diagnostis as Thomson Sattering, 6mm
mirowaveinterferometerandLangmuirprobe.
II Old Mode Disharges
With four spetrometersin dierenttoroidalpositions
wehaveobservedinoldmodedisharges,using
hydro-gen, 2-3 kHz osillations both in spetrosopy signals
asin loopvoltagemeasurement(Fig. 1).
OperationswithHeplasmadidnotpresentsuh
os-illations, indiating more stable plasma. It was also
veriedbyDopplerbroadeninglinemeasurementsthat
ion temperature in H plasmas took at least 4 ms to
reah higher values, a inrease muh slower than
ob-servedwithHeplasma[3℄.
Other diagnostis as Thomson sattering and
mi-rowave interferometer indiated also higher density
plasma: higherthan3x10 13
m 3
(uto) by
interfer-13 3
last onealsogavealoweletrontemperature: 21eV.
Inthis way, we supposed that the 2-3 kHz
osilla-tionsobserved were relatedwith high density andlow
temperatureoperation.
A very high levelof hard x-raywasobserved
dur-ingthewholedisharge,jeopardizingspetrosopy
mea-surements,sinephotomultipliersweremuh aeted.
Osillationsin old mode operationalso did not
al-lowpartileonnementtimedeterminationbyH
emis-sions,sineplasmastabilitywasnotobtained.
Figure1. Osillationsof2-3kHzpeaks,inloopvoltageand
Hlinesignalsatthreetoroidalpositions: a)LoopVoltage;
b)Hatlimiterposition(0 0
);)Hat90 0
;d)Hat180 0
III New Mode Disharges
After rst measurements with tokamak
NOVA-UNICAMP, showing osillations in plasma olumn,
high density,lowtemperatureandhighx-raylevel,we
havedeidedtotrysomemodiationsinourtokamak
to obtainbetterdisharges.
Next,wepresentthemain hanges:
Changing diode in the iruit for ore
pre-magnetization obtaining improvementof the oupling
apabilityforohmiheating.
Changeinohmiheatingandvertialeld
apa-itanebanksto getsimilar dishargesforthesebanks.
Improvementin thepre-ionizationproess
apply-ing highvoltage (1kV)betweenthetungstenlament
andasetionofthevauumhamber.
Cleaning ofthevauum hamber.
Constant heating of thehamberand disharges
withlowelds toobtainbettervauumonditions.
To show the inuene of the modiations in
dis-harges, plasmaurrent,loopvoltage, hard x-rayand
H
emissionsignalsanbeomparedin oldmode
dis-harges(Fig. 2)andnewmodedisharges(Fig. 3).
Analyzingthese gures,therstpoint tobenoted
istheabseneofosillationsinlineemissions,x-rayand
loop voltage signalsin the newmode,eliminating one
of theproblemsofoldmodedisharges.
Other important feature is the almost absene of
hard x-ray emission during the disharges, showing a
greatermodiationinoursparameters.
However,plasmaurrentandloopvoltagesignalsdo
not show yet so good resultsin this new mode. Loop
voltageis toohigh, indiatingthat evenwith theare
with vauumonditions,thelevelof impuritiesmaybe
stillhigh. Abouttheplasmaurrent,althoughthe
sig-nalsseemstobesimilar,innewmodedishargesweare
not able yet to get high plasma urrentvalues in the
seond half of the disharges, while it was ablein old
mode.
Analysisofotherplasmaparameters,asanbeseen
in next setion, showed other improvements in new
modedisharges:
Highiontemperatureinthebeginningofthe
dis-harge.
Lowerdensity.
Higherreproduibilityofthedisharges.
Widerrangeof parametersvariations(as density
Figure2. PlasmaCurrent(Ip),LoopVoltage(Lv),H
and
hardX-raysignalsinoldmodedisharge(X-raywastaken
inasimilarshot),wherespikesareseenthroughoutall
dis-harge.
Figure3. PlasmaCurrent(Ip),LoopVoltage(Lv),H
and
hardX-raysignalsinnewmodedisharge,whereperiodial
spikeshavebeensuppressed.
IV Others Diagnostis Results
The ion temperature inrease in the beginning of the
dishargeswasdemonstratedbyimpurityspetrosopy
(Fig. 4).
CalulationsofCIII 4647
ADoppler broadeningin
thetwomodesshowaquikinreaseofthetemperature
innewmodejustinthebeginningofthedisharge,
fol-lowedbyequilibrium,verydierentthantheoldase.
Another fator that ollaborated with these
mea-surementswasthedereaseofx-rayintensity,
eliminat-ing thenoise in photomultipliers and leading to more
reliabletemperaturevalues.
Mirowaveinterferometry(Fig. 5)alsoshowsan
im-provementin newonguration, with alowereletron
density(Fig. 6).
This result is not so great yet, sine still there is
resultsarebetterthanobtainedin dishargeswithold
onguration.
Figure4. CIIIion temperature innewmode(bold irle)
andold mode(triangle)disharges. Plasmaurrent(Ip)is
showninnewmodedisharge.
Figure5.Typialline integratedmirowaverowsignal.
Figure6. Eletrondensity(ne)inalowplasmaurrent(Ip)
disharge.
For Langmuir probe measurements at the shadow
of the limiter, a sinusoidal sweep voltage ontrol (
100V,500s)hasbeenused. Aoated doubleprobe
is also available. First measurements also indiated a
highdensityoperation. TypialurveI-Voftheprobe
withsweepvoltage(lowplasmaurrentdisharges)an
beseeninFig. 7. Densitiesasfuntion ofprobe
posi-Figure7. I-Vurveforsingleprobewithsweepvoltage(500
s)inlowIpdisharge,taken4mmbehindlimiter.
Figure 8. Eletrondensity variationat the shadowof the
limiter.
Thomsonsatteringmeasurementsatnewmode
dis-harges has not been done yet but rst data will be
available in the near future. Multipass system is
al-ready mounted at the tokamak (Fig. 9), and a one
hannel photomultiplier willbeusedtoobtainatleast
onegoodonditionforsatteringmeasurements.
Multihannel system (8x8 photomultipliers array)
is at nal tests phase,and will beset new inputlaser
olletionoptis,obtainingfullspatialmeasurement
a-pabilityinmultipassmultispatialsattering.
Asfor spetrosopydevelopment, 2051MPherson
Spetrometer(Visible)wasalibratedwithanEPLAB
standard tungsten lamp, and VUV Spetrometer will
be alibrated by branhing-ratio method [4℄. First Z
eetive measurements lead to values between 3 and
7, and best results will be get with full operation of
Thomsonsatteringandmirowaveinterferometer.
Forpartileonnementtimealulation,
measure-mentsarepossiblenowatnewmodeoperation. Lyman
and Balmer series will be ompared, pointing the
Figure9. MultipassThomsonsatteringsystem.
Figure 10. New multihannel assembly for VUV
spe-trosopy.
Also in spetrosopy detetion sheme, an open
MCP, using apulsed powersupply with gatedwidths
intherange: 10sto1ms,anda1024x256pixelsCCD,
Fig. 10, will be set at VUV spetrometer to obtain
Next stepfor interferometrywill be to obtain
sig-nalswithlowernoiseandanewinterferometersystem
withnouto.
Formeasurements at the shadow of the limiter, a
movableprobewithdouble and tripleprobe, isat our
plans.
V Conlusions
After rst measurements in NOVA-UNICAMP
toka-mak, modiations were performed to obtain
well-behaved disharges. Although plasma urrent is not
so high and loopvoltageneeds to derease. The data
innewongurationshowedabetterplasmaondition
withhigher reproduibly disharges, no2-3 kHz
osil-lations,higherplasmatemperatureatthebeginningof
the disharge, low hard x-ray level and lower density
(stillneedingimprovement).Newdiagnostisoperation
andothersin developmentwillallowus to obtainand
understandbetterplasmaonditionsfornextworks.
Aknowledgements
WeaknowledgeProf. Dr. MasayukiFukaofor
on-stanthelpinmanytokamakmodiationsandmaterial
supporting.
Thisworkis supportedbyFAPESP-Funda~aode
Amparo aPesquisa do Estado de S~ao Paulo, FINEP,
CNPqandCAPES.
Referenes
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pub-lishedinIVEBFPProeedings(1996).
[3℄ A. M. Daltrini, M. Mahida and M. J. R. Monteiro,
Braz.J.Phys.31,496(2001).
[4℄ M.Ueda,Braz.J.Phys.23,269(1993).
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