Aumayr, F.

Brandenburg, R.

Fiedler, S.

McCormick, K.

Petravich, G.

Schweinzer, J.

Winter, H.

English

MPG.PuRe

477Extension and optimization of lithium beam diagnostic methodsR. Brandenburg”, S. Fiedlerz), K. McCormickz}, G. PetravichS), F. Aumayrn,HP. Winter”, J. Schweinzerz) and walls Team1) Institut ftir Allgemeinc Physik, TU Wien, Association EURATOM-DEAW, A-1040 Wien2) Mawlanck-lnstitut ftir Plasmaphysik, EURATOM Association, D-SS'MS Garching3) KFKl-Research Inst., Dept. of Plasma Physics, P.U.Box 4.9, H-1 140 BudapestIntroductionLithium beam diagnostics are a multi~facetted technique for investigating fusion edge plasmas.While the determination of electron densities by lithium impact excitation spectroscopy (Li-DECS)has already reached a satisfying standard on both large fusion experiments at IPP Garching[1,2], a neutral lithium beam can also be used to determine local concentrations as well astemperatures of impurity ions by charge exchange spectroscopy (Li—(3X8) [3,4]. In order toachieve simultaneous Li—IXS and Li~CXS measurements, both existing IPP setups for electrondensity measurements have been extended. First results prove the feasibility of Li~CXS in W?—AS plasmas.In order to check the modelling of the lithium beam we have also investigated the population ofhigher Lil energy levels.EXperimental setup on W7-ASThe existing lithium heam diagnostic on the stellarator WT-AS has been extended by a 14channel CXS observation system. Two achromats (fifth: = 2.9x10‘4sr) are used to image thelight onto 14 bundles of quartz fibers, each bundle consisting of 8 single fibers (400mm. Thedetection region covers a radial range of about 13cm from the plasma center to the last closedflux surface of standard plasma configurations. For these investigations the bundles are coupledone by one to the entrance slit of a monochromator (ACTON, (Enemy—Turner, f=0.75m). Atwo-dimensional detector (Proscan CCD camera, 512x512 pixels, each 19x19um2) is directlyconnected to the monochromator exit. The spectral resolution is up to 0.018nmtpixel using alSOUg/mm holographic grating. An additional system of photomultipliers equipped withinterference filters (Er-529.0nrn) has been introduced, which can be coupled to the same lightguides for simultaneous measurements at 14 radial locations. We used the improved extractiongeometry of the ion source [1,2] to inject a beam (lud'imA) in the energy range of 20-66keV.Experimental setup on ASDEX Upgrade0n the ASDEX Upgrade tokamak the lithium beam diagnostic has a new location 33cm abovemidplane. It is equipped with a completely rebuilt 35 channel electron density optics, a 16channel charge exchange optics and a 3 channel neutral density monitoring system (fig. 1). At47835 channel 'the new position of the ion gun. which is -— ; electron deneltysimilar to the one on W7-AS. the magneticfield is weaker. There is also additional t1.—metal shielding around the ion beam. Thus,we expect magnetic field effects on thelithium beam (Ez35lteV. 1:1.2mA) to bereduced considerably.Electron density measurement setupIn the former optical system each spatialchannel consisted of three 400nm fibers. Thelight collectionftransnussion efficiency varied I -L-ir-haamdrastically from fiber to fiber and the systemwas sensitive to the beam position [5].. Toovercome these difficulties, at new head for mldplanethe fiberguides was built with each spatial ..channel corresponding to a bundle of 35 semi?“quartz fibers (lUOilSOum). The light from ‘gfeach bundle is coupled to a 43m long, 600nm - r,' ' 15ehanne] 'moncfiber (N.A.-=O.3"i) that carries the light -U.5m ' “engagedIfto the detection units. About seven percent ofthe incoming light can be dgtgctgd this way. A Fig. 1: Optical observation systems of extended lithiumnew BK? optical system. —a wedge and two beam did-“lemmas 0“ ASDEX Upgradelenses- was built to gather light into 35 channels from about 16cm along the beam path. Theobservation region can be radially shifted by a couple of centimeters, allowing it to be adjustedto different plasma Scenarios. Each detection unit is equipped with an interference filter(Ta-40%. W50.?nm) followed by a photomultiplififWe expect 5 to 10 times more signalwith the new detection system which will permit increased temporal resolution andinvestigations of density fluctuations outside the separatrix. -CXS measurement setupTwo quartz lenses (W47: = 1.5x10‘3sr) focus the light onto an array of 16 quartz fibers{400mm enabling the radial distribution of the emitted light in a 160m region around theseparatrix to be measured with 1cm spatial resolution. The fibers are coupled to the entrance slitof the same CXS spectroscopic system as described for WT—AS. Temporal resolution is limitedby the readout time of the CCD detector for 16 channels {13 ms). -Neutral density measurement setup .Two BK? lenses (£2141: e 1.8x10'3sr) focus the light onto an array of 21 quartz fibers (400m)that are grouped into three bundles. The light is gathered from a region far from the separatrixwhere lithium excitation by collision with neutrals is the dominant process [2]. Each channel isequipped with an interference filter {T>40%. FWHMSO.7nm) to select the Li(2p ~—>ZS) line.ResultsLithium boom compositionBecause of highly different cross sections for charge exchange processes, depending on theexcitation state of the donor atom, the composition of the lithium beam is an importantparameter for evaluating CXS data. We have therefore investigated several Lil spectral lines(Err—>25, 3d —->2p, 4s——>2p, rid—+213) in W7-AS discharges. While the measurements of themost relevant line map—>25) at h=6’iO.8 nm were performed for calibrating the CXS setuprelatively to the Li-IXS photomultiplier setup, all other LiI lines 'were. investigated to check theattenuation model of the lithium beam {6]. Measured intensities of emission from higher levelswere found to differ considerably (30-60%) from corresponding theoretical values. Weobserved no dependence on magnetic field strength and beam energy, whereas changing plasmadensities had strong effects on the conformity of experimental and theoretical values with thedeviation becoming larger at higher densities. 'Inadequate scaling relations for ' .Wit-AS #36762 - 36189BXCitatj'fln and ionization 012‘ I: I | | I I. l I | I l l l | I: | | | I I l- l I | I I I: Iprocesses involving protons and I ..... "01d" simulation :impurity ions in the underlying ' Emma“ “31““ '. . . “ ' tald ta "database [7] have been Identified 0:15 r“ * Exgcnmfln a Ias the major reason for these A - Jr’s-Pb -fl-r - .II' _disagreements. These are now E - _ a t —. .5 0,1being recalculated by more E“ J 4,, f ....---===_. ,, WI _ i‘ ..advanced means. First results for E _ x a _the Li(31~—>21) transitions show a 005- ' § §§ H a -significant decrease of theoretical - w -values of Li(3d)!Li(2p) ratios - -(fig.2)whenusingtheimproved DH...'...'.'.'. ......... ........._10 15 20 25cross section data. However, .beam coordinate 2” [cm]since the relative population of“15 Li(3d) 1am] in the“ lithium Fig.2: Popuiotion ratios of the Lif3ti} and Lip} energy levels.hem is in the range (if 1% ”my! Comparison of exporters-urn! data and beam simulation resnits for oWith PUPUIatiOHS 0f 3—“ (“1151' series ofsimiior W?—AS discharges. Plasma center or zufiz‘ficm.Li(nI) levels (no-2) even smaller, 'the influences on electron density calculations remain below 10%.Furthermore, recent simulations have suggested that the population of higher excited statesdepends on Zeff. Thus, the measurement of only one additional line besides the resonance lineoffers a possibility to determine an estimate for Zef-f' -under the assumption of a reasonableradial charge state distribution of the impurities and if the present disagreement for" n=3populations between simulation and experiment further diminishes as a consequence of moreaccurate cross sections.480CXS investigationsMeasurements of spectral lines of impurity ions have proven the feasibility of charge exchangespectroscopy on W‘I-AS plasmas with the extended setup. The photomultiplier system has beenintroduced for simultaneous measurements of (25+ concentrations at 14 radial locations, whilethe spectrometer system has been used for the determination of temperature profiles of (35+ ions(fig. 3).Wit-AS #39360 - 39363 warms #393551600 '- I I I I I I I I I I | I | I I I F ._ D36 _I I I I I l‘I I I I I I I I I I I I I I | I I I I r I I I ._:. a) _‘ E b 31400 : I 05+ : 015 :- ) J1200 :— ——E— 0* E : :: : 4 L _"1000 —- _, 0' ~ ,- : : a 2 ill :5-4 Z : a : 'i - ”w . :000 E" "E .3 012 - If. i" m” We ~400 j— —j :Il. 0 : : 0,1 ;20 t" _ '1 :l C—pellet "EU A I I I I i I I II I i I I I I i I I' I I D L l_! I I a I i I I 1 l I r I I I I I I I l I i r I I I I I I.0 5 10 15 20 0 0,2 0,4 0,6 0,8 1 1,2 1,4 1,6Rflfl= [cm] [[5]Fig. 3: a) Radial temperatare profiles of 05+ compared to e‘ [8] and 13+!9i. All data were obtained daring a seriesof similar W?-AS discharges. 0) Raw photomaltt'plt'ar signals for concentration evalaation at Refit-=12.3cm.injection ofa carbon pellet at t=0.8s increases the charge exchange induced signal significantly. Injected lithiumcarrent lg;- =2mA at En48ltV. 'Temperature values, which were corrected for line broadening effects such as Zeeman splittingand lalevel mixing [10], are similar to protonfdeuteron as well as electron temperamre profiles.Evaluation of impurity ion concentration values requires extension of the charge exchange crosssection database, which is presently being carried out.AcknowledgementsThis work has been supported by Friedrich Schiedel - Stiftung fiir Energietechnik and by Komniission earKoordination der Kernfusionsforschung at the Austrian Academy of Sciences.References. 1. K. McCormick et al., IPP Report HIKE}! (1995)2. S. Fiedler, IPP Report IIIrQGQ (1995)3. E. Wolfram et al., Rev. Sci. lnstram. 64 [1993) 22854. F. Aumayr er al., J. Nacl. Materials 196-198 (1992) 9235. J. Schweinzer et al., 22th BPS Confi, Earophys. Conf. Ahstr. 19C III {1995} 2536. J. Schweinzer etal., Plasma Phys. Contra Fasten 34 (1992) ll'l3'I'. D. Wutte et al., At. Nacl. Dar. Tables 65 (1‘99?) 1558. HJ. Hartfass et al., Proc. 8th Workshop on ECE and ECRH. Oxford (198”!) 2319. M. Kick et al., 20th EPS Confi, Earophys. Conf. Alisa. DC I (1993] 35?ID. R.P. Schorn et al., NacLFasion 32 (1992} 351

Extension and Optimization of Lithium Beam Diagnostic Methods

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Extension and Optimization of Lithium Beam Diagnostic Methods

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