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(EX2/5) Profile Control and its Effects on Plasma Confinement in Heliotron E

T. Obiki, T. Mizuuchi, F. Sano, H. Okada, K. Nagasaki, K. Hanatani, Y. Ijiri, T. Senju, K. Yaguchi, K. Toshi, K. Sakamoto, T. Hamada, H. Funaba

Institute of Advanced Energy, Kyoto University, Uji, Japan

K. Kondo, S. Besshou, H. Zushi, M. Wakatani, Y. Nakamura, M. Nakasuga

Graduate School of Energy Science, Kyoto University, Uji, Japan

V. V. Chechkin, V. S. Voitsenya

Institute of Plasma Physics, National Science Center ``Kharkov Institute of Physics and Technology'', Kharkov, Ukraine

K. Ida, S. Sudo, M. Sato, S. Kobayashi

National Institute for Fusion Science, Toki, Japan

S. Kado, K. Muraoka

Interdisciplinary Graduate School of Engineering Science, Kyushu University, Kasuga, Japan

K. Matsuo
Faculty of Engineering, Fukuoka Institute of Technology, Fukuoka, Japan

Abstract.  The effects of the plasma profile on the global energy confinement have been studied in Heliotron E with special regard to differences between heating methods (ECH, NBI, and NBI + ECH). With high power NBI, peaked T_i and peaked n_e profiles ( T_i(0)/$\langle$T_i$\rangle$ $\leq$ 2.7, n_e(0)/$\langle$n_e$\rangle$ $\leq$ 4.5) were simultaneously archieved under low recycling conditions. A peaked n_e profile ( n_e(0)/$\langle$n_e$\rangle$ $\geq$ 2.5) could lead to the high T_i mode where the ion heat transport in the central region is substantially reduced. By changing the ECH launching condition (on-axis, off-axis and toroidally oblique injection), the peakedness of the T_e profile could be controlled in the range 1.3 $\leq$ T_e(0)/$\langle$T_e$\rangle$ $\leq$ 4.5. A peaked T_e- and flat n_e-profile ( 3.5 $\leq$ T_e(0)/$\langle$T_e$\rangle$, n_e(0)/$\langle$n_e$\rangle$ $\leq$ 1.8) was brought about by the well focused on-axis ECH. The ECH plasma with peaked T_e profile has higher stored energy than that with a moderately peaked T_e profile for the same injected ECH power and the same density region. The global energy confinement time normalized by the LHD scaling, $\tau_{\mathrm{E}}^{\mathrm{G}}$/$\tau_{\mathrm{E}}^{\mathrm{LHD}}$, showed n_e(0)/$\langle$n_e$\rangle$ dependance for the low T_i mode NMI plasmas. For the high T_i mode, the n_e(0)/$\langle$n_e$\rangle$ dependance of the $\tau_{\mathrm{E}}^{\mathrm{G}}$/$\tau_{\mathrm{E}}^{\mathrm{LHD}}$ was weak. These findings suggest that the LHD scaling should be modified to scale the global energy confinement of the helical plasmas in a wide range of n_e(0)/$\langle$n_e$\rangle$.

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