(TH/P29) Statistical characteristics of turbulent transport dominated by zonal flow dynamics
T. Matsumoto^{1)},
Y. Kishimoto^{2)1)},
J. Q. Li^{2)}
^{1)} Japan Atomic Energy Agency, Naka, Ibarakiken, 3110193 Japan
^{2)} Graduate School of Energy Science, Kyoto Univ., Uji, 6110011, Japan
Abstract. Characteristics of ETGdriven turbulent transport dominated by zonal flows and nonlinearly generated large scale structures with low toroidal/poloidal wave numbers are investigated by gyrofluid simulations in slab geometry. Main results found in this research are as follows. (i) The zonal flows change the characteristics of turbulence from "homogeneous" structure to "inhomogeneous" one, in which microscale vortices and nonlinearly generated macroscale vortices coexist at different radial zones, exhibiting a twoscale nature in turbulence. (ii) The fractal dimension is simultaneously reduced at any radial region with an increase of the ratio of zonal flow energy to that of total fluctuations, accompanied by the disappearance of exponential PDF tail of the heat flux. (iii) The reduction of heat flux in strong zonal flow regime results from two mechanisms in the relation between poloidal electric field and pressure perturbation, i. e. the reduction of coherence in the zone of microscale vortices and the phase synchronization in that of macroscale ones. Namely, macroscale vortices, which is an origin of low fractal dimension and plays a role to saturate zonal flows, is survived in the system without causing large thermal transport by adjusting the phase relation.
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