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S. Masamune, K.Y. Watanabe, S. Sakakibara, Y. Takemura, F. Watanabe, S. Ohdachi, K. Toi, H. Tsuchiya, Y. Nagayama, Y. Narushima and LHD experiment group
Mode structure of global MHD instabilities and its effect on plasma confinement in LHD
Date of publication:
22 IAEA Fusion Energy Conference, EXS/P5-11
The LHD magnetic field configuration is characterized by high magnetic shear with low magnetic well or magnetic hill configuration particularly at the plasma periphery. Therefore peripheral m=1/n=1 mode plays important roles in high-beta regime in LHD. In the present study, the m=1/n=1 mode has a resonant surface very close to the outermost flux surface. Relationship between the magnetic fluctuation arising from the mode and internal structure of the mode has been studied using soft-X ray emission profiles. It has been found that the rotating m=1/n=1 mode with magnetic fluctuation level of 0.04%, mode amplitude of 3% and mode width on the major radius normalized to the plasma minor radius of 16% (6% in minor radial direction) brings about 10% degradation of the H factor. The mode amplitude, rather than the magnetic fluctuation amplitude, is shown to be a good parameter in characterizing the effect of the mode on plasma performance.
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