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)

    Realization of high-Ti plasmas is one of the most important issues in helical plasmas, which have an advantage for steady-state operation comparison with tokamak plasmas. Since 2010, newly installed perpendicular-NBI with the beam energy of 40 keV has been operational in the LHD and the total-heating power of perpendicular-NBIs increased from 6 MW to 12 MW. Such low-energy NBIs are effective for ion heating and enabled us to achieve a higher Ti than that obtained previously [1]. In the last experimental campaign, ICRH-discharge cleaning was adopted to reduce particle recycling from the wall. As a result, NBI-heating-power profile became peaked and the density-normalized ion heating power in the core region increased by 18%. In the LHD, high-Ti plasmas have been realized in combination with a carbon pellet [1-3]. The kinetic-energy confinement was improved by a factor of 1.5 after the pellet injection. Figure 1 shows the typical time evolution of (a) the port-through NB power, (b) line-averaged-electron density, (c) the radiation power, (d) the plasma stored energy, (e) Te0, (f) Ti, (g) the radial profiles of Ti, Te and ne in the high-Ti discharges, which recorded the highest Ti0 and (h) the progress of the achieved Ti0 in the LHD as the dependence of Ti0 on the density-normalized ion heating power Pi/<ni>. The plasma was sustained by three tangentially injected NBs and two perpendicularly injected NBs with the total-port-through power of 27 MW and the column-shaped C pellet ( = 1.0 mm, l = 1.0 mm) was injected at t = 4.57 s. One line of the perpendicular NBIs was modulated for Ti measurement by CXRS. After the pellet injection, the central Ti, dTi/dreff at the core region clearly increased indicating the formation of the ion-ITB. On the other hand, there was little change in Te0. The radiation power increased just after the pellet injection but went back to the previous level due to the formation of the impurity hole. Ion temperature of 7 keV at the plasma center was successfully obtained and the achieved Ti0 has been increasing approximately linearly with Pi/<ni>. ICRH-discharge conditioning exerted a preferable effect also on quasi-steady-state operation of high-Ti discharges without C-pellet injection. The sustain time of the plasma with Ti0 > 4.5 keV has been successfully extended to 1 s from 0.5 s, which is the previous record, even the PNB was 4 MW lower than that of the previous one.    1) O. Kaneko et al.:Plasma Fusion Research 4 (2009) 027. 2) K. Ida et al.: Nucl. Fusion, 49 (2009) 095024. 3) K. Nagaoka et al.: Nucl. Fusion, 51 (2011) 083022. 01020PNB [MW](a) #110599 Tang. x3Perp. x2012n e_fir[x1019 m-3](b)C pellet012Prad [MW](c)00.51Wp [MJ](d)024T e0 [keV](e)024684.6 4.7 4.8 4.9 5 5.1 5.2T i_CXS [keV]0.030.310.600.76(f) reff/a99Time [s]012345678-0.6 -0.4 -0.2 0 0.2 0.4 0.6reff [m]Co-NBIdominant,PNBI  = 26 MWTiTene(g) #110597T i, Te [keV], n e [x1019 m-3]0123456780 2 4 6 8~2009  2010  2011Pi/<ni> [x10-19 MW m3]NBI, He+Cpell.(h)Fiscal yearT i0 [keV] Fig. 1. The typical time evolution of (a) the port-through NB power, (b) line-averaged-electron density, (c) the radiation power, (d) the plasma stored energy, (e) Te0, (f) Ti, (g) the radial profiles of Ti, Te and ne in the high-Ti discharges, which recorded the highest Ti0 and (h) the progress of the achieved Ti0. 6§1. Extension of Operational Regime in 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)(2) Mission Research Themes

Extension of Operational Regime in High-Ti Plasmas in the LHD

Extension of Operational Regime in High-Ti Plasmas in the LHD

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