Confinement improvement in high-ion temperature plasmas heated with high-energy negative-ion-based neutral beam injection in the Large Helical Device

Y. Takeiri, S. Morita, K. Ikeda, K. Ida, S. Kubo, M. Yokoyama, K. Tsumori, Y. Oka, M. Osakabe, K. Nagaoka, T. Shimozuma, M. Yoshinuma, K. Narihara, H. Funaba, M. Goto, S. Inagaki, K. Tanaka, O. Kaneko, A. Komori, O. Motojima

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Abstract

An increase in the ion temperature due to transport improvement has been observed in plasmas heated with high-energy negative-ion-based neutral beam injection (NBI), in which the electrons are dominantly heated, in the Large Helical Device. When centrally focused electron-cyclotron-resonance heating is superposed on the NBI plasma, the ion temperature is observed to rise, accompanied by the formation of the electron internal transport barrier (electron-ITB). In the electron-ITB plasmas, an increase in a positive radial electric field is observed, and the transport analysis indicates that the ion transport in the half-radius region is improved with a reduction of the anomalous transport. Thus, this ion temperature rise is ascribed to the ion transport improvement by the transition to the neoclassical electron root. In high-Z plasmas, the ion temperature is increased with an increase in the ion heating power and reaches 13.5 keV. The central ion temperature increases with an increase in a gradient of the electron temperature in an outer plasma region of ρ = 0.8, suggesting the ion transport improvement in the outer plasma region induced by the neoclassical electron root. These results indicate the effectiveness of the electron-root scenario for obtaining high-ion temperature plasmas in helical systems.

Original languageEnglish
Pages (from-to)1078-1085
Number of pages8
JournalNuclear Fusion
Volume47
Issue number9
DOIs
Publication statusPublished - Dec 1 2007
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Nuclear and High Energy Physics
  • Condensed Matter Physics

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    Takeiri, Y., Morita, S., Ikeda, K., Ida, K., Kubo, S., Yokoyama, M., Tsumori, K., Oka, Y., Osakabe, M., Nagaoka, K., Shimozuma, T., Yoshinuma, M., Narihara, K., Funaba, H., Goto, M., Inagaki, S., Tanaka, K., Kaneko, O., Komori, A., & Motojima, O. (2007). Confinement improvement in high-ion temperature plasmas heated with high-energy negative-ion-based neutral beam injection in the Large Helical Device. Nuclear Fusion, 47(9), 1078-1085. https://doi.org/10.1088/0029-5515/47/9/002