A. Wakasa

Group High-T

H. Lee

H. Takahashi

I. Yamada

K. Ida

K. Nagaoka

M. Osakabe

S. Murakami

Y. Takeiri

National Institute for Fusion Science (NIFS-Repository)

  In the 15th experimental campaign of the LHD, high Ti plasma was obtained by the wall conditioning using the ICRH discharge. In the operation in combination with the ICRH-discharge conditioning, the central ion temperature of 7 keV has been achieved and has exceeded the previous record of 6.4 keV. Figure 1 shows the time history of (a) the partial pressure of H2, (b) He in the experiment, (c) and (d) the expanded waveform and (e) Ti0 and the line-averaged-electron density in a series of discharges. The spikes observed in fig. 1 (a)-(d) correspond to the plasma discharges. Two-hour titanium gettering was done before the experiments. The ICRH-discharge conditionings with the maximum-pulse duration of 12 s, in which the NBs were not injected, were carried out in #111167-111196 and #111216-111238. The main gas in the high Ti discharges was H2, on the other hand He was mainly used in ICRH-discharge conditioning due to the effective minority heating by ICRH. Figure 2 shows the radial profiles of (a) Ti, (b) ne and (c) the ion heating power normalized by ne for #111165 and #111199 at t = 4.74 s, when the maximum Ti0 was obtained. In #111165 the achieved Ti0 was below 6 keV. The ne profile formed the hollow shape implying the large-particle recycling from the wall. After that 30 discharges of ICRH was carried out and then the lower electron density with the parabolic profile and the Ti0 exceeding 6 keV were obtained. As shown in fig. 1 (c) and (d), the partial pressure of H2 and He during the discharge of #111165 were lower than those of #111199 even the partial pressure of He just before the discharge was larger because He was used as the working gas for the ICRH-discharge conditioning. This represents the decrease of the outgassing from the wall, namely decrease of the neutral-particle recycling. However the preferable condition for high Ti maintained only a few discharges. In #111212, the attained Ti0 got below 6 keV due to the degradation of the wall condition. Then 23 discharges of ICRH was done resulting that the decrease of the neutral pressure, the parabolic profile of ne and the Ti exceeding 6 keV were obtained again (#111243). The increase of Ti0 after the ICRH-discharge conditioning is considered mainly due to the increase of the NB-heating power per ion at the core region by the decrease of ne as can be seen from fig. 2, not the improvement of the ion-heat transport. 10-810-710-610-510-410-3H2 Pressure [Pa]#111165 #111199#111212 #111243Long pulseICH dischargesLong pulseICH discharges(a)10-810-710-610-510-410-311:00 12:00 13:00 14:00 15:00 16:00He Pressure [Pa]#111165#111199 #111212 #111243(b)10-810-710-610-510-410-311:10 11:20 11:30H2HePressure [Pa]#111165(c)10-810-710-610-510-410-312:50 13:00 13:10H2HePressure [Pa]Time [H:M]#111199(d)4567800.511.52111200 111250Ti_3.796ne_firT i_CXS7_3.796 [keV]n e_fir [x1019 m-3]Shot Number(e) t = 4.74 s#111165 #111199#111212 #111243Exp. start#111161~ICH discharges ICH discharges Fig. 1. The time history of (a) the partial pressure of H2, (b) He in the experiment, (c) and (d) the expanded waveform and (e) Ti0 and the line-averaged-electron density in a series of discharges. 01234567#111165#111199(a)T i [keV]012(b)n e [x1019 m-3]00.10.20.30.40.50 0.2 0.4 0.6 0.8 1reff/a99(c)Pi/ne [x10-19  MW/m3 ] Fig. 2. The radial profiles of (a) Ti, (b) ne and (c) Pi/ne for #111165 and #111199 at t = 4.74 s. 11§6. Impact of ICRH-discharge Conditioning on Realization of High-Ti Plasmas in the LHDTakahashi, H., Osakabe, M., Nagaoka, K., Yamada, I.,  Ida, K., Takeiri, Y., High-T Group,  Murakami, S., Wakasa, A. (Kyoto Univ.),  Lee, H. (Univ. Science and Technology)

Impact of ICRH-discharge Conditioning on Realization of High-Ti Plasmas in the LHD

Impact of ICRH-discharge Conditioning on Realization of High-Ti Plasmas in the LHD

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