T." "Mutoh

National Institute for Fusion Science (NIFS-Repository)

§27. ICRF of High Density and High Stored Energy Plasma with High Proton Concentration Mutoh, T. In LHD, a high stored energy plasma was obtained by applying the NBI and the ICRF pulses to the high electron density plasma fueled by multi-pellets of hydrogen. The fuelled gas for start-up before pellets injection was helium or hydrogen. In both cases, major ion specie was proton, and helium ions existed as the minority specie. In normal density conditions, ICRF heating was applied to the plasma of helium majority and proton as minority ion species. In this case, the wave power was mostly absorbed by the minority protons[!]. However, in high-density plasmas maintained by NBI (H-beam), wave-heating mode was quite different because protons were majority[2]. In Fig. 1, time evolutions of the high stored energy plasma are shown. ICRF power of 2 MW was additionally applyed to the 5MW NBI at the time of 0.9 to 1.4 sec and the stored energy increased up to 1.03MJ at the electron de:qsity of 1.0 X 1 020m-3. In this discharge, plasma was fueled by helium gas puff and hydrogen pellets as appeared in the time evolution of electron density. The concentration 6 §' 4 ~ c 2 rL 0 1.0 15 G) S' E ~ 10 ~ '"";.o.s 0 or-~ -Q) c: 0.5 1.0 1.5 2.0 Time [sec] Fig. I Time history of NBI and ICRF power and plasma stored energy, Wp, at high density plasma. The contribution of ICRF was around lOOkJ. (#24443, B=2.8T, Rax=3.6m, 38.47MHz, Helium gas-puff and H2 pellets, PNB1=5MW, P1cru;=2MW, with LID Island collection and CH4 conditioning) of protons to total ions was around 0.9. These data show that ICRF fast-wave heating is useful for high density and high proton concentration plasma with the presence of NBI beam. Theoretically, fast-wave mode of ICRF has no density limit. And the coupling of antenna and plasma confinement are improved as density increasing. These tendencies were also observed in the experiment. In Fig.2, the increment of stored energy due to the additional ICRF during NBI heating is shown on the wide plasma density range. Three heating modes are plotted. Square marks represent minority-heating mode and the open circles are data for hydrogen pellets injection mode with helium gas puffing. This mode means that majority ions are hydrogen and the proton concentration measured by the particle fuelling was from 60 to 90 %. Closed circles are for the hydrogen gas puffing and 32 hydrogen pellets fuelling. This mode was a fundamental cyclotron heating of hydrogen plasma. The heating properties of both pellets plasmas are almost same and it implies that minority helium ion has a small role in the ...... EE He(H:minority) .., =. c. 150 EEl 3: H2 pellets( He puff) -E±J383 0 -100 EEl El3 0 c:: G) em • E 0 G) 50 Oo~ ~ • 0 .E 00 12 Fig.2. Increments of plasma stored energy by ICRF to NBI plasma by changing the electron density. heating mechanism. In Fig.3, the resonance and cut-off surfaces at the LHD cross-section are shown. Plasma parameters are of the typical discharge with hydrogen pellets and helium gas-puffing. In case of pure hydrogen discharge like close circles of Fig.2, there is no lines of S and Lin Fig.3. In both cases, wave damping is mainly related with the cyclotron resonance fficH in the figure. In high density plasma, fast-wave, having right-hand polarized electric field, has very small damping rate. However in LHD, efficient heating performance of around half of the minority heating mode was observed. The presence of NBI beam and the large non-uniformity of heliotron field are the candidates of the large damping rate of the fundamental cyclotron heating of the fast-wave. References [1] Mutoh, T. et al., Phys. Rev. Letts. 85 (2000) 4530 [2] Mutoh, T. et al., in Proc. of Int. Congress on Plasma Physics, ICPP-2000 Quebec, Vol.III (2000) 840 ... I C{L LHD Wall P g.3 Resonance and cut-off surfaces (RIL: Right-hand and Left-hand cut-offs and S: Two ion hybrid resonance and rocH: Cyclotron resonance ) on LHD cross-section at high electron density and high proton ratio. (B=2.8T, 38.5MHz, IIeo=lxl020m-3, nHI(nH+nHe)=0.6) 

ICRF of High Density and High Stored Energy Plasma with High Proton Concentration

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