Energetic-Ion-Driven Global Instabilities Observed in the Large Helical Device and Their Effects on Energetic Ion Confinement

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概要

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• This paper reviews various global instabilities destabilized by tangential neutral beam injection (NBI) in the Large Helical Device (LHD) plasmas. These global modes are toroidal Alfvén eigenmodes (TAEs), which are also observed in tokamak plasmas, and helicity-induced Alfvén eigenmodes (HAEs) which are observed only in three-dimensional plasmas such as LHD plasmas. Moreover, reversed magnetic shear Alfvén eigenmodes (RSAEs) are observed in a reversed magnetic shear (RS) plasma in the LHD, where the sign of the magnetic shear changes from positive in the plasma central region to negative in the plasma peripheral region. The RSAEs exhibit a characteristic frequency sweeping due to temporal evolution of the rotational transform profile. In the RS plasma, the energetic-ion-driven geodesic acoustic mode (GAM) is also excited. The GAM interacts nonlinearly with the RSAEs and generates a multitude of frequency sweeping modes through a three-wavecoupling process. The TAEs and GAM exhibit various types of nonlinear evolution, that is, pitchfork splitting and rapid frequency chirp-up and/or chirp-down. The linear and nonlinear characteristics of these energetic-iondriven global instabilities in the LHD are compared with those observed in tokamak plasmas. TAE bursts having rapid frequency chirp-down induce redistribution and/or loss of energetic ions. Future important issues are briefly described.

著者

• TOI Kazuo

  National Insitute for Fusion Science

関連論文

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• Progress in Impurity-Related Physics Experiments in LHD
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• Two-Dimensional Measurement of Electron Density Profile in the Edge Region of the Large Helical Device Plasma by a Sheet-Shaped Thermal Lithium Beam
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• A Simultaneous Spectroscopic Measurement of the Global and Edge Local Structures in the Ion Temperature and Plasma Rotation Profiles in the Compact Helical System
• Development of an Array System of Soft X-ray Detectors with Large Sensitive Area on the Large Helical Device
• Tangential SX Imaging for Visualization of Fluctuations in Toroidal Plasmas

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