Eberhagen, A.

McCormick, K.

Murmann, H.

English

MPG.PuRe

35 P 3 A1 09 q-PROFILE MEASUREMENTS IN THE CENTRAL PLASMA REGION OF ASDEX K. McCormick, A. Eberhagen , H. Murmann and the ASDEX Team MPIPP, EURATOM Associat ion, Garching, FRG Abstract : Using the Lithium-Beam-Spectroscopy (LBS) technique /1/ q-profile measurements have been carried out in the central regi on of diver t ed , ohmic ASDEX plasmas over a range q(a)a2.9-5.3 for ne-1x10 1 'cm-•. The e xperimental results are consistent with a flat q(r) profile ha ving q(o) -1~0 . 06 and exhibiting a sl i ght t endency towards lower ~(o ) for decreasing q(a). Motivation : Previous LBS meas ur ements /2/ of q(o) in ASDEX for q(a) -3. 3 gave q(o) -1 duri ng ohmic heat ing. On TEXTOR q(o)<1 is measured over the range q(a)=2. 1-6. 3 /3/ , whereas on TEXT q(o) is determined t o be related to q(a), having q(o)>1 for large q(a) and vice versa. In order to provide a broader data base for comparison with these findings, the LBS techni que is used to investigate q(o) for a variety of q(a). Experiment: The q(a) scan i s performed in four discharge series whose par ameters are l i sted in Table 1 along with the deduced q(o) values from neoclassical resistivity (NR) and LBS, as well as the sawtooth (ST) inversion radius rsT from LBS, NR (here rq=1 is equated to rsrl and elec-tron- cyclotron-emission (ECE). Three series have two Ip plateaus each, thereby enabling the relative 6q(r) to be monitored more precisely since each plateau has a common measurement base line. The fourth series features a radial displacement of the plasma (R -1 66.5-163 cm) over 0.8 sec to achieve a moderate r adia l scan within one shot. Except for q(a)•5.3, where it is not certa:n, ST are present in all series with 6Teo/Teo-5-8% . Series #1 is with hydrogen, the others with deuterium. Based on NR, Zeff-4 -6! The density ne of -1x10 1 'cm-•, plasma currents and toroidal fields chosen represent a balance between optimizing the LBS signal (low ne, high Bt) and the hindering of runaways (high ne, low Ip)· Based on the gathered experience a larger q(a) range than covered here is accessible. Results: Tte LBS technique measures the local magnetic field pitch angle 6p=tan- 1 (Bp1Btl· Figure 1 illustrates the noise level end temporal behavior of ep(t) for series Nol at several values of the flux-surface radius rf. The corresponding pitch angle ec profiles, adjusted to cylindrical geometry , are plotted in Fig . Ca; the values represent average5 over 200 ms around the given time points, hence ST activity is completely averaged out. The representative error bar reflects the base line uncertainty (direction of B~ - accounting for -2/3 of the total - and of es itself . 5—PROFIL IormiI CH ssoci t archi: thiu -Bea -S e -le eas o i a oi 'erted, l s » 3 fi —Ix1013cm‘3ri nt 00 Lstp , ) e li i~ :0.0 iL llg e C( [3iH rJ- ,( ):,Au fi : 3‘ imn' ’E: 1.11,' ea 8 i’: EuLLHK JH U u ier‘is ffl n Ler i1 ,A\ V DE4 , ‘ - Fo gn Hi w LN 59f VJF uZei iqnw : t ;: {wa sw rm gr ln g w§E1LNOI Q(" x‘ : ‘ uu7r; ~y i ul'iLa‘ :,Ldwwnm w wwl‘iuR‘MOlwffi *uw"1 : r : 7H” udqw i h*wtfl' “ »3i ‘3; 2y;Strai ght-line fits t o the es data ln the centra l r egion , correspon-ding to a constant q(=rf/RtaneS> . yield q(o )-1 . 06 and 0 . 95 for t= 1 and 1 . 8 sec , respectively . Although neither Thomson scattering nor ECE profiles are available for corroborat ive evidence , the rf(q=l , t=l .8) - 15 . 2 cm value matches the rf(q=1)~ 1+a/q(a) (1+40 . 2/2 . 93=14 . 7 cm) scali ng of the other ser i es . By the same account , rf (q=l) for t=l sec should be -8 . 6 cm , meaning that only two measurement points are inside the expected q= l surface , which is not adequate to character ize q(o) . The 2nd series was plagued with x-rays to the extent that no reasonably r eliable 8p measurement was possible . Nevertheless, the series serves t o show that the rf(q=l) radius derived us ing neoclassi cal resis tivity, under the assumpt i on of a f l at elect ric field- and Zef f-profile , corresponds well with rsT · For the 3rd series , x-ray development again disturbed the diagnost i c going into tre second Ip plateau . Fig . 3 i llustrates that up to th i s point , 8p changes little in the inner region . The es (rf , t=l .0) plot of Fig . 4b yields q(rf<9 cm)-1 . 01±0 . 12 . For comparison, as and q derived from neoclassical and Spit zer conductivity are also presented . T~e t ypical broadening of the Te profile in response to a decrease in q(a) is demo1mtrated in Fig . 3a . Figure 3b serves both to convey an impress i on of the err or bars on the Te-based calculation of eg over the series , as well as to conf i rm that a perceptible change in eg vs q(a) i s to be expected onl y for rf>10 cm . The four th series produced only a very marginal scan i n rf of -o . 6-1 . 1 cm due to the fact that 6p is interrogated along a line inclined about 59° to the midplane . Nevertheless es (rr>4 cm) in Fig . 4c is well documented : q(rf<11 . 2 cm)-1 . 0 ~8 : 8~ ; rsT-12 . 1 cm and rf(q=1)=12 . 9 cm f or neoclass i cal resistivity . Discussion : Within this limited data base , vary i ng Qa over 5 . 3-2 . 9 has ostensibly altered q(o) from - 1 . 06 to o . 95 . However , not enough radia l points were present within the potential q•l s urface to convincingly descr ibe q (o) f or q(a)•5 . 3 , and at q(a)•2 . 9 the uncertainty in eg encloses q(o)=l. One might fault the linear eg data fit with i n q= 1; notwithstanding , a close examination of such furn i shes no compelling mot ivation to introduce any other algorithm in the cent ra l region . With i n any one ser i es , local excurs ions of q(r) from the indicated value cannot be precluded , but may be regarded as unlikely when considering the overall direction of the results . The experimental data are not consistent with the neoclassical prediction that q continues to monotonically decrease within rq•l . On the other hand , the better agreement with the Spitzer profile :s probably specious : Quite systematical ly - over a wider parameter range than presented here - Spitzer resist iv ity fa i ls to correctly give rsT and for low-q(a) , sawtoothing discharges it often yields q(o)> l. In s hort , i t is necessary to invoke neoclassical effects to approximatel y describe the exper imental situation . The discrepancies within rq=l may be at l east partially at t ributed to two effects : a) Due to the absence of points near the plasma center and the fit function chosen , the Te prof_le i s taken t o be more peaked than in f act . (See Fig . 3a) , b) The calculations assume a uniform E- field over the plasma cross section , wh i ch is known to be i nval i d in the presence of ST /5/ . W: g l ne t SC i tr l w ,i t iu / og), 0 1.0 9 e1, cti l . t i t n L1H leu n i Fo idw w 1, 1 ~ 3(q:1)%1 3/ ( l HO.?/? : U 3 iJEViES- t t iqs 1 h ~8 hl ‘ Dr ”airr , u : Charact ca [Hii p13:19 ig-110).Y—Piyol ia 0J ure ci H15 i . l ‘ . SeriS i :1 a 51asisti i su nt l t ield— R i—le, ies l PSr , t i rbe i tte 19 . . i listrates i t,0 tle . u 05 i , in i . Uhi ~1 13 . n; Tl$TH 0g i: si l hi cti i 1‘30 wh cic : f i >3 )i l . a onS . oi le‘hds l 0% nr , l (: f r r ti ”pl ‘ f>1r i ~0.1 03 i i r' n l i ineif“ the' a5 f i 3 us in hfli .? ; in 13 1 .j =1l<‘; “ encl si i ti .fli hin ni n qi n ih l i ,. r l. . it o l =1 a nvincinqr (i , =3 rt i i BBi :1 ine 93 n =hxaminati ish3 lloti tro l nt l i ir e , l \: ” ai ‘1 n iul Vi ie, l L i t r l::,n t5e a. lqsnii 0l0 01l01ii r ,i f .8a i : S i i l i rit/0 i t ills r ctl “Sl ( , t t i s 1 Ic c kw l r f ir r i t l n t hr i . [ J :w i lrti l t ribute u : :5: ' t iintal .na F t r f.in 7 l u .i -fi SHL in, i ot l.100 0 100 0 100 0 50 0 50 0 0 50 0 -50 0 - 50 0 -50 0p[mrod] ~1122078 196 /"""" .... / ..,..,..,,,,._ :022077 ~ .. 22083 .. 22082 6 ~#22075 76 5 ~ -3.7 .. 22085 - 7.2 .. 22084 - 9 .6 ~"22086 I p (100 kA) n,[1013 cm" 3 ; ; 22087 o_J.l!._~~~~~~~~~~--t--o 0.5 1 1.5 2.5 t [sec) Fig. 1: Temporal behavior of the meas ured pitch angle 0p• fie and Ip for series #: 1. Fig . 3 : (a) Te profiles from the YAG Thomson scattering sys tem at t-1 . 0 and 1. 8 sec for seri es # 3, (b) Pitch a ngle profiles derived f rom Te profi l es averaged over the series , assuming neoclassical resistivity . 37 9 p [mrod] 100 ~ "' 23539 0 100 ~ fr 23538 0 0 ~ -50 - •. 1 fr 23532 0 ~ -SO .. 23533 -6.l I p [lOOkA) ;;, [101Jcm· 3] 0 0 O.S l l.S 2.5 t [sec] Fig. 2 : 0p(t), for series # 3. fie and I p J+-~~~~~.....-~~~~~-;-T, (keV) e~[mrod] 100 50 # 23531 II 23530 - JS o+-~~R_o~d_iu_s_r-'+~-m~]~~~-+ 0 10 20 30 40 ig—i—iéEJM’mImI] ”with!“ 1C9 Lmr M]““0 l '- 233L111 1"100‘ ”WI , ‘\ ’.’ II : 307d ‘ _ V—y-“Auwrf'1‘ ‘y 4‘4 4'II I ‘1 f/ r 15 6 Lm‘U wryO a100 19 B r m" "' ‘00;, ,AJ-mup-wr 10 20J.n.'mi,-\f‘4W\/\~l 3:: 23535"Ir ' f“n 50 7 7 —0., . 4m» .4.‘0” IS I J]! ‘v 0 —~::;-—————f,1'~~»~"\“”' it 5 “kt/ - 5 _ A I it7 ”fl 7 7 i—JJV‘\J\/L-’~‘J.fi0 7‘ ”NH/”J It 5 \J‘x... \i 507 ~we,” WNW/M “ 2353350/'~ 12 5 A5AD .. V/fi«WM/W“Manon 3I D UkA‘L/fl“5 762‘ fix// “[10'3c 3] \‘O I—.1- /ej__—\\\* , .LeeeeemAlaJmM' \Jx-n. ” 22065 0 0 5 I ‘5 2 25~ 7 ‘ [sec]0 fig_5“: F_i . : e “e .)V\w-M~\,«AX. -72 ’VV‘MZOS,‘ ptfi0__, *—7_50. \M‘NWJ‘H 22086I [ v] 1: 7 1-7x—— ~ ,.\‘—|2.0 2‘ . “j 3‘’SOl mlnzom (=18n .; ‘- 'l7 a b 5_ ‘ , 9 a In“,910581: ‘3 1.,..O Radius 1] [cm] a ° 3,L0 20 O 20 :20. i, ,4tt , 38:0 I IS 2/ 0'‘1359‘5\as e , n D \1. "10:2?“3 lett t "= . r e 3,tc les r ero les Radius "[cm10r , i i Dow" 10 "jg—r3i ti i . 'i11 11 1: '·'· 38 Table 1 : Experimental Parameter s and Results ----Series/Shot Bt(kG) Cp(kA) q(a) ----- q( o )------LBS NR -------rsr---- -- -LBS tJR ECE 1 : 22075 -88 21 194 5 . 3 1 . 06 ~~ . 8 I I I I 348 2 . 93 0 . 95 ::6 . 05 I 15 . 2 I I 2 : 22929-48 21 . 6 228 4.7 2 I 0 . 63 I 9 . 5 9 . 5 3118 3. 06 I 0 . 67 I 13 . 7 14. 0 3: 23524 - 39 23 249 4 . 55 1 .01::o .1 2 0 . 59 9 11 . 2 11 . 0 348 3 . 22 I 0 . 65 I 13 . 6 13. 8 4 : 23634 - 4 ll 22 . 8 299 3 . 77 1 0+0 .05 0. 62 11. 2 12 . 9 12 . 2 . -0 .04 e~ [mrad] • 22075-BS 100 ;.-~- o.... a 100 e~ [mradJ i: 2352L-J9 100 e~ lmradJ (f ', d "' c t/ 1.8s \ b .~ " . :::;:.~~ ,';· ~ ft•·· j -..._ l " "] / ,. . so 50 . ' ::- 2363L·H I • 1? - Eroer1ment ) - Exot 1.0s - - - ,'feoclass1col -- - lleoc l ! ········ Spitttr ········ Srurzer Radius r 1 [cm l Radius r, [cml r 1 [cml -10 10 2J 30 LO -10 10 20 30 LO -10 l " w I _) / I ..... I q 11.2 ! ~·· .: " .• 1.0 J -so .· j ~/· f·· ~ ____ ... ~ 1.0 l 1.0 j • r . I f 0.8 / 0.5 0.6 -100j Fig . 11_:_ Pitch angle profiles vs the flux s ur•fa ce raditJS r r f or: (a) f i rst ser i es , at t - 1. 0, 1.8 sec near the end of each Ip plat eau. The cor res pon-d ing q(rr) de pendence 1Jeri ved f r om q(rrl~rf/RtaneS is also gl ven . (b ) T~ i r d ser i es , during the f irs t plateau at t-1 sec; CanpArison among the Meas ured eg pc ints and es profi les bas~d on neoclassical and Spi t zer resistivity a nd associat ed q- prof i l es . The nrrow indic•tes rsr fran ECE . (IC) J!"ourth series : • R-166 . 5 , /':,. R-1 63 . 9 cm . Refer ences : - ----- -Iii K. McCormi ck , Cour se on Di agnostic Techniques for rusi•rn Pl;isinas , Vol. Ir , (Var P.nna , 1986) 635 . I?/ K. McCormi ck , r . X. S~l dner , et a l. , Proc . 13th EPS Conf ., Vol . 2 , (5chliers~e . 1986) 323 . 131 H. Soltwisch , H. Stodi ek , et al ., Proc. o f t he ll th [ AEA Conf . on Plasma Phys i cs and Control led Fus ion Research , Vol. 2 , (Kyoto , 1986) 263 . /4/ W. P. West , D. Thomas , e t al. , Phys . Rev . Let t . 58 ( 1987) 2758 . 151 r . Alladlo , et al. , Pr oc 12t h EPS Conf ., Vol. 1-;-(Budapest , 1985) 138. f , - r"): 4m 1 . v. ; / x‘, ? A x 1*} .4 /3: .?‘II‘J L'9 “ .6 ‘4. ' q C,H u.- C)? .73 11* ‘)Ly1‘»:V.)[‘JLU—‘r.)mx]{\JU1OWNLU(DUI)LA.):4 .33fi 11-1M I' \I‘ [J 0 w ‘4" [ ]. ,, wt L~1.0, .3 HF ) lqlwu . T e correspan—jing q(Fr) depu fi ou d rive F o ( f)=rf/Rtannfi in 4130 iv . (5)'T11"‘l.hw‘h‘3, Jri‘ W F sL *wgalw Efijgwfinn ni H? r file iej a:x:hwmr ';¢l Gpgtg ranfiiqtm - rofi “°. 4V“a :14101193 w<4.? c .a > 13'3. . A ~itc l le Fl SH“F1UW wadiuu Pf For: (a) first.‘l‘lu 5- 50v} Jomgarisgr RMMHE thpstiv1fly HHJ‘L[H‘mr'fi‘r’l -,.~."iw PIHQWAS,d1ontr l aion minnf. anF, ( mt , 985)FUL‘ .’N/ U. ) , Gt 31., NOV. PLL. NH (1987) £758./5/ F. ilnflln, at 31., r EBEH _)HF. H3. , (Un apwj' 1935‘ 138.

q-profile measurements in the central plasma region of ASDEX

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q-profile measurements in the central plasma region of ASDEX

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