T. Ido, A. Shimizu, M. Nishiura, S. Nakamura, S. Kato, H. Nakano, Y. Yoshimura, K. Toi, K. Ida, M. Yoshinuma, S. Satake, F. Watanabe, K. Itoh, S. Kubo, T. Shimozuma, H. Igami, H. Takahashi, I.Yamada, K. Narihara and the LHD experiment group
Potential Fluctuation Associated with Energetic-Particle Induced Geodesic Acoustic Mode in Reversed Magnetic Shear Plasmas on LHD
Date of publication:
22 IAEA Fusion Energy Conference, EXW/4-3Rb
Geodesic acoustic mode(GAM) driven by energetic particles are observed in the Large Helical Device by a heavy ion beam probe. The GAM frequency shifts upward in plasmas with monotonic magnetic shear. In plasmas with reversed magnetic shear, on the other hand, the observed GAM and the energetic-particle induced mode, which is probably reversed-shear induced Alfven Eigenmode(RSAE), appears, and the GAM frequency becomes constant. The GAM in the reversed-shear plasma localizes near the magnetic axis. It is confirmed that the energetic-particle induced GAM is accompanied by the electrostatic potential fluctuation and the radial electric field fluctuation. The amplitude of the potential fluctuation is several hundred volts, and it is much larger than the potential fluctuation associated with turbulence-induced GAMs observed in the edge region in tokamak plasmas. The energetic-particle induced GAM modulates the amplitude of the ambient density fluctuation at the GAM frequency.