(TH/P2-21) Multi-Scale-Nonlinear Interactions among Micro-Turbulence, Magnetic Islands, and Zonal Flows

A. Ishizawa1), N. Nakajima1), M. Okamoto1), J. J. Ramos2)
1) National Institute for Fusion Science, Toki, Japan
2) Massachusetts Institute of Technology, Massachusetts, USA

Abstract.  We investigate multi-scale-nonlinear interactions among micro-instabilities, macro-scale tearing instabilities and zonal flows, by solving reduced two-fluid equations numerically. We find that the nonlinear interactions of these instabilities trigger macro-scale MHD activity after an equilibrium is formed by a balance between the micro-turbulence and zonal flow. This MHD activity breaks magnetic surfaces then this breaking spreads the micro-turbulence over the plasma. These multi-scale-nonlinear interactions can explain the evolution of fluctuation observed in torus plasma experiments because micro-turbulence and MHD instabilities usually appear in the plasma at the same time, in spite of the fact that effects of micro-turbulence and MHD instabilities on plasma confinement have been investigated separately. For instance, MHD activities are observed in reversed shear tokamak plasmas with a transport barrier related to zonal flows and micro-turbulence, and micro-turbulence is observed in Large Helical Device plasmas that usually exhibit MHD activities.

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