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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 $\rm T_i$ and peaked $\rm n_e$ profiles ( $\rm T_i(0)/\langle T_i \rangle \leq 2.7$, $\rm n_e(0)/\langle n_e \rangle \leq 4.5$) were simultaneously archieved under low recycling conditions. A peaked $\rm n_e$ profile ( $\rm n_e(0)/\langle n_e \rangle \geq 2.5$) could lead to the high $\rm T_i$ 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 $\rm T_e$ profile could be controlled in the range $\rm 1.3 \leq T_e(0)/\langle T_e \rangle \leq 4.5$. A peaked $\rm T_e$- and flat $\rm n_e$-profile ( $\rm 3.5 \leq T_e(0)/\langle T_e \rangle$, $\rm n_e(0)/\langle n_e \rangle \leq 1.8$) was brought about by the well focused on-axis ECH. The ECH plasma with peaked $\rm T_e$ profile has higher stored energy than that with a moderately peaked $\rm T_e$ profile for the same injected ECH power and the same density region. The global energy confinement time normalized by the LHD scaling, $\rm\tau_E^G/\tau_E^{LHD}$, showed $n_e(0)/\langle n_e \rangle$ dependance for the low $\rm T_i$ mode NMI plasmas. For the high $\rm T_i$ mode, the $n_e(0)/\langle n_e \rangle$ dependance of the $\rm\tau_E^G/\tau_E^{LHD}$ 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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