Becker, G.

Bosch, H.

Brambilla, M.

Braun, F.

Brocken, H.

Bäumler, J.

Eberhagen, A.

Fritsch, R.

Fußmann, G.

Gehre, O.

Gernhardt, J.

Gierke, G.

Glock, E.

Gruber, O.

Haas, G.

Hofmann, J.

Hofmeister, F.

Izvozchikov, A.

Janeschitz, G.

Karger, F.

Keilhacker, M.

Klüber, O.

Kornherr, M.

Lackner, K.

Lenoci, M.

Lisitano, G.

Mark, E.

Mast, F.

Mayer, H.

McCormick, K.

Meisel, D.

Mertens, V.

Mueller, E.

Murmann, H.

Niedermeyer, H.

Noterdaeme, J.

Pietrzyk, A.

Poschenrieder, W.

Puri, S.

Rapp, H.

Roth, J.

Ryter, F.

Röhr, H.

Schneider, F.

Setzensack, C.

Siller, G.

Smeulders, P.

Speth, E.

Steinmetz, K.

Steuer, K.

Söldner, F.

Vollmer, O.

Wagner, F.

Wedler, H.

Wesner, F.

Zasche, D.

MPG.PuRe

21 ICRF B-MODE AND ZOco/D(B)-KINORITY HEATING ON ASDEX K.Steinmetz, F.Wagner, F.Wesner , A.Izvozchikovl, J.-M. Noterdaeme, F.Ryter2, J.Baumler, G. Becker, H.S.Bosch, M.Brambilla, F.B r aun, H.Brocken , A.Eber-hagen, R.Fritsch, G. Fussmann, O.Gehre, J.Gernhardt, G.v.Gie rke, E.Glock, O.Gruber, G. Haas, J.Hofmann, F.Hofmeister, G.Janeschitz, F.Karger, M.Keilhacker3, O.Kluber, M. Kornherr, K.Lackner, M.Lenoci4, G.Lisitano , E.van ~1ark1 F. Mast, H.M. Mayer , K.McCormick, D.Meisel, V.Mertens, E.R.Muller , H.Murmann, H.Niedermeyer, A. PietrzykS, W.Poschenrieder, S.Puri, H.Rapp, H.Rohr, J .Roth, K.-H. Schmi tter, F.Schneider, C.Setzensack, G.Siller, P.Smeulders3, F.Soldner , E.Speth, K.-H.Steuer, O.Voll mer, H.Wedler, D.Zasche Max-Planck-I nstitut fur Plasmaphysik, Euratom Association, D-8o46 Garching, FRG INTRODUCTION I CRH experiments in t he ASDEX divertor tokamak have now been operated in· the 2~H regime and D(H)-minority mode. This paper presents the status of these investigations and compares some of the most interesting features of the RF scenarios with neutral beam heating (NI) in the same machine under optimized and reproducible plasma paraoeters. The achievement of the H- mode with ICRH alone is reported . Considerations on possible synergetic effects of the combination of ICRH with NI /l/ and impurity studies during ICRH /2/ are presented separately. 20cH (67 MHz) and D(H)-heating (33 . 5 MHz) experiments sre being routinely conducted in excess of 2 MW launched power for pulse lengths of up to 1 s. In addition to the combined scenarios of NI + ICRH, pure 20cH and D(H) heating up to maximal power have now been applied in extensive studies of diverted discharges and in the case of carbonised walls /3/ . EXPERIMENTAL RESULTS Electron and ion heating properties of both RF scenarios are compared in Figs. 1 and 2. Di rect central electron heating (Fig. l) measured via the initial s lope of the sawteeth is clearly higher in the minority mode than at 2~H· The electron heating efficiency, ne 6Te(O)/pi~e of about 4 . 0 and 1.8· 1013 eV/kW cm3 , for D(H) and 2f.CH (H-plasma), fespectively, is al so higher in the minority case (nH/ne "' 0.05), which , however, was partly due to the better confinement properties of deute rium plasmas . Figure 2 presents the ion heating at RF power below 1 MW: The minority regime exhibits an efficiency as high as the NI H-mode (4. 2 ·1013 eV /kW cm3, H0 ~ D+) /4/, which is consistent with the good confinement observed at that RF power level (see Figs. 4 and 5) . Now t o the global heating efficienci es of the various scenarios: Recent investigations on 2~H-heating and its combination with NI gave rather promising results /57. When combining ICRH with NI , an important question is whether the RF heating efficiency becomes improved with increasing Ti (target) or by coupling of the IC wave to the fas t beam particles . In the case of carbonised walls where heating is not degraded by deleterious impurity r adiation , the increase of Ti due to NI preheating (Fig. 3) !Academy of Sciences, Leningrad, USSR; 2cEN Grenoble, France; 3Assigned to JET J oint Undertaking, Englan!l; 4ENEA Frascati, Italy ; Sunive r s ity of Washf ngt"on, Scn tt lP, 11"=,\: MIN 0 0 Fig. 1 : 3 :l: 40 -~ .... o .. :z 30 % ~ ~ a.."' 20 '::::! c;, 3 <l 10 00 200 400 ... tiii0-19, o · ·plosmo • t lSJS.:.·60, H·-p(osma 600 800 P1c (kW) Direct e-heating of m eH and D(H) scenarios. NI+ ICRH (2QcH I "o with .. • • + * w 10 wall cor b. .. 0°- o· • !CRH .. H0- o• • ICRH • • • • o0-W•ICRH , ~·'. , , , , , .. ... • • I[ I'!.W pt/~c : NI •ICRH H0-W + ~-!*i----t,..--tt--*-NI only D.W ~~ !L -model 22 • • ,,., •.• ,. o· -plasma. ex l lrf'l + • u•e• -c.& . H•-ptoSRJ . CX IIIH~ DIHI ft,"'fi.·4T,IOI/P!P Pd~p=0.6PIC • Ja,=S.S·l01ltV/kWual ~ IC 0 200 400 600 P1c (kW) ~ Ion heating for both ICRF regimes. 150 + • 198 lt..19790·97 . w/o carbon.. Ptl:2 MW A • 1991.6-SI. corbon1zfd , w/o NI 9 • 19B90-90t.,corboruzed. w/o NI • • 1917S·B9, w/o corbon.,w/o NI 800 + + :1+ wilh N1 .. 10'-0'1 ~ 100 so 0 0 w/o NI 6 "'~ OH .,v '! , ' , f> 0 NI only 0 NI only 2 Ptat (MW) ~Plasma energy versus total heating power for D(H), NI and NI+D(H) heat ing 3 Fig. 3: Heating efficiencies of 2nCH• NI and NI+2ncH improves the IC efficiency only by about 25 % from about 20 kJ/MW (w/o NI , Ti "'0. 5 keV) to 25 kJ/MW at PNI ~ 3.5 MW (Ti"' 2 . 2 keV). Coupling of the IC wave to the beam is in fact observed in eX-s pectra, but obvious ly to a n extent whi ch is not s ufficient enough to improve the heating : On comparison of ICRH discharges with additional Ho+ o+ or D0 + ~ (Fig. 3) the RF ef fic i ency turns out to be independent of the beam spec i es . Owing to the isotope effect on confinement 2ncH- heated di scharges in deuterium and helium with a small amount of hydrogen (nn/ ne > 10 %) show even better efficie ncies (D0 +o+ + ICRH in Fig. 3) . No heating at the fourth IC harmonics of o+ and 4He2+ could be noted. i -23 As a general feature, energy and particle confinement of ICRH-heated plasmas are systematically better t han those of the NI L-mode but appear still within the combined error bars. The plasma energy for minority heating at low power scales as well as the ohmic phase (Fig. 4). With increasing RF power Wp bends towards an L-mode behaviour, staying, however, at a slightly higher level than NI. In combination with NI, Wp and thus TE are improved, too, a feature also observed at 20cH /5/. The energy confine-ment times of 2f.CH, D(H) and NI(L) modes normalized to the ohmic values are presented in Fig. 5. Careful experimental investigations on the RF power absorption lead to a • 0.6 and 0.7, without and with beam preheating respectively. For pure NI heating a= 0.8 to 0 .9 was found, in good agreement with the beam deposition calculations. As shown for various 20cH regimes, carbonisation strongly reduces the central radiation /2, 3/, thus improving the confinement. At high power (Pie~ 5 PoH) both RF scenarios reach about equal TE ( ~ 0.6 T~) while below 700 kW the D(H)-confinement still remains as good as the ohmic one. Assuming equal global heating efficiencies ( ~ 20 kJ/MW2 for the D(H) and 20 modes, but with wgH (D(H), o+-plasma) > ~H (20CH • H+-plasma) the superior confine-ment of D(H) at low power in comparison to 20cH can be explained. 1.5 w. 0 IHI , rorbc:nztd a 0 Htl . non-tortlOI'l 2 AcH . carbrnud + 11lcH , hloAIUtl gtoll. • 20cH rltoowoll - NI l · !Ndr . r..E0 ~9Sms. , a.~0.6 9S•s. . 0.6 85 ms . 6.6 80 as . 0.6 60~ . O.b Cltii., t ~oE> NI-L reg1me o+-----~----~----~----~ o QS w ~ 2n P1c(MW) Fig. 5: Normalized confinement times versus launched RF power for various heating scenarios. "E u ..... d N ;:!> ;:!> 1.5 1.0 0.5 2ncH -. 1 1868819972 ++ 6. OIH) Nl~9. ++• IH'-0"11!> coroon~zfd wall n • • S.7·10uuf1 •••.,• .:o~ OH p~ 6 P~es1.8HW,T,I20un lz 1 18keV -+ Pc:1,5HW.T,I20tf"'ls092ktV 0 PNI:::1.7 HW .f,t20crn): I 04 ~eiJ • P0 :0,4 HW ,T.I20cmh0 -,0keV ... 0 0+-----r-----r-----r-----~ 0 10 20 30 40 r (cml Fig. 6: Normalized Te profi l es of OH , NI, 2nCH and D(H) Rather narrow power deposition profiles ore expected theoretically for ICRF heating. In fact, ICRH is accompanied by Te profiles strongly peaked on axis (Fig. 6) confirming a rather local power deposition . Well outside the q • 1 zone, however, the profiles of OH, ICRH (20 , D(H)) and NI appear to be almost invariant if normalized toTe at r ~ a/2 indicating a 'profile consistency' within the so- called confinement zone /6/. When the IC resonance layer is shi fted from the plasma centre to half radius, the Te profile does not vary much while the global hea ting i s maintained with slightly reduced sawteeth amplitude. ICRF H-mode studies have been performed with and without NI. In combination with NI under optimized conditions the additional ICRF power can switch the plasma into the H-mode. For the first time, the H-mode has 24 been achieved with ICRH alone in the D(H)-minority regime at an absorbed RF power of about 1.1 MW. The H-mode is marginally reached showing all characteristic signatures of rising ne and Wp, and frequent ELMs (Fig. 7). The typical development of an edge electron temperature pedestal is also # 12927 60 ~ 19 927 ::::; 1.0 ICRH [O(H)J :. 1.0 .. • t = 1.258 3: sec 20 ... , ' 0 t = 1. 342 sec > .. , ' I. (I) 0.5 - ... , ~ 7E ' ' H" "' •, u ...... 0 ' ~ 2 'e-. ' 'e, .. L" IC:~ 0 .... 20 30 40 so 1.2 1.3 1.1. 1.5 r (cm) tls) Fig . 7: Transition into the H-mode ~Development of the edge of an ICRF-heated plasma. Te profile in the ICRH L and H-phsse. observed (Fig. 8) which is rather similar to the behaviour found with NI heating /7/. The occurrence of a short ELM-free H-phase (see Fig. 7 at t = 1.365 s) gives rise to a shrinking of the scrape-off-layer and changes the antennae coupling to such an extent, however, that in all cases one of the RF generators terminates operation by voltage breakdown in the vacuum line when operating at the RF power limit . To keep the H-mode with ICRH somewhat higher RF power than available at present appears to be necessary. CONCLUSIONS Global heating and confinement of 2P~H and D(H)-regimes are found to be almost equal at high RF power and appear to be well comparable to or even somewhat better than the NI L-mode . For the first time ICRH has now shown the potential to access the H-mode . ACKNOWLEDGEMENTS The kind help of J . Winter and P. Wienhold (KFA Jilli ch) in providing the CD4-gas for carbonisation, and the excellent support of the ASDEX, ICRH and NI operation teams are gratefully acknowledged. REFERENCES /1/ F. Wagner et al., this conference . /2/ G. Janeschitz et al., this conference . /3/ w. Poschenrieder et al., this conference. /4/ A. Stabler et al., Proc . 4th lnt. Symp. on Heating in Toroidal Plasmas, Rome, Vol. I (1984) 3. /5/ K.Steinmetz et al., Plasma Physics and Controlled Fusion 1!!._ (1986) 235 . /6/ H. Murmann et al., this conference . /7 I M.Keilhacker et al., Plasma Physics and Controlled Fusion~ (1984) 49. 

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ICRF h-mode and 2<sub>CH</sub>D(H)-Minority heating on ASDEX

ICRF h-mode and 2<sub>CH</sub>D(H)-Minority heating on ASDEX

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