Characteristics of turbulence dominated by zonal flows and large scale structures

Matsumoto, Taro; Kishimoto, Yasuaki*; Li, J.*

In order to find rules to identify turbulent dynamics in tokamak plasmas, we studied the statistical characteristics from gyrofluid simulation for electron temperature gradient (ETG) turbulence in sheared slab configuration. The statistical characteristics such as fractal dimension, Lyapunov number, probability density function (PDF) are investigated in details for various turbulent structures dominated by intermittency, zonal flow, and nonlinearly excited tertiary waves. High dimensionality (d 8-10) and prominent exponential PDF tails are observed in turbulent plasmas, which exhibit an intermittent transport dynamics. The PDF tails are found to shows a prominent similarity insensitive to the plasma parameters such as temperature gradient and magnetic shear. On the other hand, in plasmas dominated by zonal flows and tertiary waves (Kelvin-Helmholtz), which is established in weak magnetic shear regime, a significant dimensionality lowering (up to d 3) is observed accompanied by disappearance of the exponential tails. The relation among different statistical values will be discussed.