Wave-Number Spectral Characteristics of Drift Wave Micro-Turbulence with Large-Scale Structures

Abstract

Wave-number spectral characteristics of drift wave micro-turbulence with large-scale structures (LSSs) including zonal flows (ZFs) and Kelvin-Holmheltz (KH) mode are investigated based on three dimensional gyrofluid simulations in a slab geometry. The focus is on the property of the wave-number spectral scaling law of the ambient turbulence under the back reaction of the self-generated LSSs. A comparison of the spectral scaling laws between ion/electron temperature gradient (ITG/ETG) driven turbulences is presented. It is shown that the spectral scaling of the ITG turbulence with robust ZFs is fitted well by an exponential-law function 〈varphi2/2〉E ∝ e−λkx in kx and a power-law one in 〈varphi2/2〉P ∝ ky−β in ky. However, the ETG turbulence is characterized by a mixing Kolmogorov-like power-law and exponential-law 〈varphi2/2〉E ∝ e−λkx, ykx, y−3/(1 + kx, y2)2 scaling for both kx and ky spectra due to the ZFs and KH mode dynamics, with λ and β the slope index factors. The underlying physical mechanism is understood as the spectral scattering caused by the back-reaction of the LSSs on the ambient turbulence. These findings may provide helpful guideline to diagnose the plasma fluctuations and flow structures in experiments.