Eberhagen, A.

Fußmann, G.

Gruber, O.

Janeschitz, G.

McCormick, K.

Murmann, H.

Roberts, D.

Roth, J.

Röhr, H.

Steuer, K.

Wagner, F.

English

MPG.PuRe

31 P 3 A1 08 Zerr-PROFILES IN DIFrERENT CONFINEMENT- AND HEATING REGIMES OF ASDEX K. -11 . Steuer , H. Rohr , D. E. Roberts*, A. Eberhagen, G. Janeschitz , G. Fuemann , O. Gruber , K. McCormick, H. Murmann , J . Roth , F. Wagner *A tom i c Energy Corp ., Pr et oria , RSA Max-Planck-Ins ti tut fUr Pl asmaphysik EUR ATOM Associat ~on , Garching , FRG Introduction Zeff i s an impor tant quan t i ty i n f usion r esearch . It s hould i deall y be as sma~ l as possible to mi nimize both fuel di l uti on and radiation losses . Further , radial prof i l es of Zeff• together wi th Te( r ) , ar e needed to derive j(r) used in stabil ity analys i s . We report measurement s of Zeff prof iles for a variety of ASDEX plasmas : ohmi c (Hand D; gas and pellet fuelli ng) , and co and counter neutral beam heated pl asmas . Zeff measurements -~ Zef f profiles are measured from the intensity of plasma radiation in the near infrared . In this wavelength region recombination and li ne radiation are gener all y unimportant and the r adiation is ma inly br ems-strahl ung . The intensity profiles are measured wi th the ASDEX 16 channel YAG laser Thomson s8attering sys t em (Fig . 1 ) / Ref . 1/ . Each of the 16 detecti on boxes conta i ns 3 broa3band int erference filters set a t wavelengths of 850 , 950 and 1000 nm. This provi des a means of checking the A-2 scaling of br emsstr ahlung int ensity and gi ves an approximate measure of the absence of line r adiat i on. Up to the sil icon a va-lanche diodes used as detectors , the system i s identical to t hat used f or Thomson scat-t er ing . For the Zerr measurement s , however , a DC- coupled circui t with a band•1idth of 5-0 kH z i s used . The sample rate is typically 200 Hz . Compar i son of the Abel - inverted radiation with hydrogen bremsstr ahl ung determined from s i multaneously measured ne and Te profiles r esults in Zeff prof il es ·- . . " . -.. : . : .· . .:: -.. : .. Fi g. 1: Bremsstrahlung Zeff set up from +20 cm to -33 . 5 cm with a spati al r esolution of about 3 cm . Under some conditions comparisons have been made with rad i al l y averaged Zeff values from plasma res is t i vity a nd f r om sawtoo th analysis. The lat t er method is based on the electron power balance in ohmi c d i schar ges , in t he plasma centre , during t he peri od o f r ecovery after Lhe sawtooth crash /ref . 2/ . In addition, Zef f has been est ima t ed f r om impuri t y dens ities deri ved by two methods . Firstly, absolutel y measur ed VUV li ne int ens i t i es of the fo ur dominant impuriti es (Fe , Cu , 0, C) are compared with t hose calcul ated by a time dependent : mpurity transpor t code using measur ed ne and Te profiles . b G DrL5* l (3 JHW"L“R WeCOrli“: H rm u, H rn .mi r . r tu ,Irvl’l‘iIJv—Planck-Instit FHr lnn phyJiHHH ssociatio , arcnl c, Ui eLnnL anti n un IL 3 nl‘tle n i i i l a lllllfinnnfll ‘infil Fililfilfl l“- ,‘w WIFE} '1‘“ ('1') wr‘f‘ mI-j‘ IJz rfllH91" rlfi. A n uwwudAn w ' Wort : n'3 1 fi. r . malt ilegi [H . K Dl n ~l h tem n.tre oCwntflil” d terlerence lteno 3L veln gh , lUOOIMn l rn n rn a l‘2ali 9 FUlj iven n c.1 nt onl w intiwn.lJHD1'”; l“ r‘v’rfl .~‘fui] 11,1"e 1:.33 Ll wl »“V t'j3l1'lr,;jdiL WY lhu H r . H ‘<iv": L“:roma wvwrafiwl “H JeSk iltte‘ l wt n 15”ulrw POWOP l U i Wl’uhdl' m ho l .~t w, L w wri d lw th nd lcw 0 u . 1 .llln wr nu: n o a “i L' ro i ri v ni nn nr vr agM . 2'lrml. j,l nhnnlut aonrr HU l ng i w niliwn Hf Fofl inn l i u itimm , , U l i [HUSH y u lilfl h”1wul , f ans mr a w ‘url dWLNHV“ti v vw ‘ wlnn w u“ iw 7 L32 From ttis comparison an independent density prof ile i s obtained for each impuri t y species , allowing its Zeff contribution to je calculated . Secondly , the densities of the two light impurity species (0, C) can be also derived from charge exchange recombination spectroscopy (CXRS) resulting in an independent measurement of their Zeff contribution . These spectroscopic Zeff are generally less accurate than bremsstrahlung Zeff but the resulting impurity densities yield considerable insight into the Zeff behaviour reported in this paper . Results and Discussion Axial v3lues of Zeff as a function of ne for steady state ohmic and co- NI heated discharges are shown i n Fi gs . 2 and 3 , Normal ly , Zeff is found to decrease with increasing ne, to be higher in D+ than in H+ plasmas , and higher in NI than in ohmic plasmas . The VUV Zeff are in good agreement with the bremsstrahlung Zeff• as are the sawtooth Zeff for OH discharges in H+· The CXRS Zeff must be normalized to one point f r om the bremsstrahlung measurements because optical components of the CXRS diagncstic , inside the vacuum chamber, have been inaccessible to direct calibration . The CXRS Zef f then Shuw the same trends with ne · The above behaviour can be understood from the spectroscopic resul ts . In ohmically and NI heated discharges O and C ar e the dominant light impur-ities with O giving the largest contribution to Zeff · The VUV results for a transition from OH ~ co-NI heated plasma a r e shown in Fig . 4 for H+ and Fig . 5 for D+ . The dominant heavy impur ity in the H+ discharge is Cu . It originates from the divertor plates and is more impor tant at lower den-sities and in NI than in OH discharges . The densities of C and O (measured by VUV and CXRS) do not change strongly with ne so i t is this fact , together witt the decrease of Cu , that explains the decreaae in Zeff with increasing ne · Fe is unimportant in H+ discharges due to carbonization , but gives a significant contribut i on to Zeff in D+ discharges where the walls were not carbonized (Figs . 3 and 5) : Particularly int eresting are the Zeff r esults obtained in three rather different scenarios in which i mproved energy confinement is found in ASDEX . These are OH discharges in D+ with reduced gaspuff (Fig . 2) /Ref. 3/ , pellet fuelled OH discharges (Fig . 6) /Ref . 4/, and counter-NI heated discharges (Fig . 7) /Ref . 5/ . In these cases there is a reversal of the trend of Zerr decreasing with increas i ng ne which shows that the improved energy conf i nement is accompanied by improved particl e confinement . The strong accumulation of light impur i ties in counter NI discharges can be seen from the 08+ (Fig . 7) and c6+ densities . The rel ati vely slow init ial increase of n08+ and nc6+ leads to a decrease of Zeff as in the normal co- NI case . However , the impurity density increase is much steeper later on , so that Zeff incr eases during the phase when the global energy confinement is also increasing . For counter- NI the neoclassical Zeff is in good agreement wi th the bremsstrah-lung Zeff ~nd this is also true for the OH pellet case (Fig. 6). In the improved confinement OH regime Zefr(r) shows slight peaking at the plasma cent re at later times (Fig .8) but this is not seen in the pel l et (Fig . 9) or counter- NI discharges . si ri , l i f t De l .condl , m lities i ri DFr :‘:c i ctru copl i a i L t .t f r ll l c s Mi n ‘l i i r i: llSlaJi frit r fil4 11 ’ Functi D—HJ n i . . r a l , f i; , .1 ft f , f Fo i i-ga i ro tH z ti , ii l . H fs o H .i Spectr ul .Oh i l i l i rie 0 i l t f -i + i U i. i purit 1.inate i orti i i i 3ls t l h ,r si i H . i r i ti i ic t io f ir )rti l e ffer r pr XS f ,l l J . f. u t r H. f. .i ff 2 in Q i r inemei rt e f . t e lal l i uri .(1° i . l v w i re 0 Cl :rea f - l ri ri i re t f reasr l .i i f i tf a i For lff lnt ll .ter— .t+33 Summary The prese~t measurements have shown a wide variety of behaviour of z ff in ASDEX plasmas and Zeff values ranging from 1.2 to -5 have been r~und. In particular, for three different improved energy confinement regimes, the Zeff results indicate correspondingly improved particle con-finement. Ref. 1 Ref. 2 Ref. 3 Ref. 4 Ref . 5 H. ROhr , K.-H. Steuer et a l . , Nucl. Fusion 22 (1982) , 1099 A. Eberhagen, Internal Report IPP III/124, 1987 E.R. MUller et al., this conference O. Gruber et al , this conference 0. Gehre et al , Phys. Rev. Lett., to be published Zeff lco-Nrl .. , ""'· Cu I • DflENS Y VUY o oms ~~. 0 ......  di---=~ . 'H-·tQ 0 c-"• <10 1Jcm-J> Fig . 2 : Zeff as a function of ne for OH-plasmas in hydrogen (H) and deuterium (D) . s~~~~~~~~~~~----. 5 Fig. 3: Zeff as a function of ne for co-NI heated plasmas i n H and D. z eff ~----'~-'-il~_OT No. 22287 4 lco-N1i z ff SHOT No. 4: e I CO-NI I 22631 ) 2 NI 1.0 12 1.4 16 l.B 2.0 lime lsl Fig . 4: bremsstrahlung Zeff and the VUV imp. contribut ions during a trans ition from OH~co-NI in a hydrogen plasma . 3 2 D ... .. Fig. 5: Fe Cu c bremsstrahlung Zeff and the VUV imp. contributions during a transition from OH~co-NI in a deuterium plasma . —5snt ur ent i f i r fZeff l s a f . t -fo . i l f t iffe t i r r fi tf i l i r rti l c -1 o r l , l. i ( ), 1099II/12Hf. 3 ulle lf u 0. l,f O l, . t lis7 7 Talillfi I IY I‘Vv VUV V VZeff IOH' - Sakooll- u cxn‘ \ ImprovedTE regime)H \':\\“\\»7fl/////K/A/7 \§2\\ ““:‘—’—u__a_‘_, d‘~»oi_ K'v \ 0., k-\. 'QneHO'Jcm'J) ne(I '3c '3){75*2';é‘¥“s iiiéé;i f 8 - i fast )5SHOT No. 22287 > ‘00-NlSIIOI No. 3|5 Zeff4"[A 18 U 1lime [s] llnlels]. N t f t t ft ionsi H+co- I i.tr ioni rom H+co- I it r34 "' ne(YAG) m n0 o• I CTR-NI 1 ·1 '--------j 12 density / 12 )" -- ltJ ·:r: '!3 I Ill u ,.-• = ~8 D / ll~ / . ~ ~ c: neocl. calc. r ~ .. I ->~ ~---1 _._._ PELLETS Ll ( ( ! time[sl 10 11 l2 lJ l4 lS 1.6 Fig . 6: Time dependence of "e (above) and Zerr (below) in a OH pellet refuelled discharge in hydr ogen . s~-~~~~~~~~~~~~~ Zeff SHOT No. 22990 b 3 a radius (ml -0.4 0~2 0.0 0.2 Fig .: 8: Radial profiles of Zerr for OH discharges in deuterium. (a) "normal" regi me, (b) improved co~finement regime (r,e0 -~.6 x 1013cm-3, see F'ig. 2) . / I, ,.4J' '£l .-h-,..-"-Zeff 3 v 2 + Ill <lJ ~ I'\) lrllU,.f'!,,'ll't'll•t<)IH • ltftt0rrm1ll21.,0ql +1r111cxns11·100l"°9J , _____ 11_:1.::.Cc..T.:..:H_-:...I _;.:.N.:_I --~_,_I__, "' •-;) c: I, U.li l.U V. 1.8 . [ I l1111e s ~ Time dependence of ne and no8+ (above) and Zeff (below) in a counter NI heated discharge in deuterium . ]- ----- - - - - - - -Z eff S~OT No. 22276 2 0 I = 1.25 s 0 oo'>oo0 0 0 0 0 0 0 0 1 ' radius [ml r -0.4 -0.Z 0.0 0.2 f'i§·: 9: Radial prof lle or Zeff for a pellet fuell"d OH discharge in H (see Fig. 6). --: ' I L.)InOH PELLETSdens”), smr Mo, 22:73Hu w l l ‘ ~L“ f I .I— />E TT“‘—\; - _4,«*”'- EJ -I O I t Vt \ 1 l I li e [SPH 12 I] M 15 ISi . :18:gff lc C IL:oauaaaoag:lLA [U.L a; 3 d:: i les f 2CE LSCh ES nForeff: PLume. ( ) i rnf fiem : r ih ):6 € io‘ficm‘E,g ,3 ( ):_r F?‘ FJI g oa'ne(|0[4cm‘3) f "nuI TH~J HI. qn ,/ itw¥ '” w*,vx1/,; w ‘¢ m:4‘, 9‘gw v.V,HHNNMH;HW' ZIHH‘TPHIWHI V " "“,Fpnumwumwwm‘1' ‘ V. - +v v v 7_ v _+.+ bNU 14 fl ,him: [3]: at “ :0 * :ez Zxt r .rx)x rJLI} «1.r—vm-rHW-uwo w [ l {-- 2 GD 1i ; 0file Df ~rl r eLa

Z<sub>eff</sub>-profiles in different confinement- and heating regimes of ASDEX

http://hdl.handle.net/21.11116/0000-0009-4312-7

Z<sub>eff</sub>-profiles in different confinement- and heating regimes of ASDEX

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