Phase dependent advection-diffusion in drift wave - zonal flow turbulence

TL;DR

This paper investigates how phase dynamics influence plasma turbulence, challenging the random-phase approximation by analyzing phase coupling effects using stochastic oscillator models in a simplified turbulent system.

Contribution

It introduces a study of phase interactions in plasma turbulence, highlighting their role in self-organization and coherent structure formation beyond traditional approximations.

Findings

Phase dynamics significantly affect turbulence evolution.

Coupling of modes alters the characteristic time scales.

Results suggest the importance of phase considerations in turbulence models.

Abstract

In plasma turbulence theory, due to the complexity of the system with many non-linearly interacting waves, the dynamics of the phases is often disregarded and the so-called random-phase approximation (RPA) is used assuming the existence of a Chirikov-like criterion for the onset of wave stochasticity. The dynamical amplitudes are represented as complex numbers, $\psi = \psi_r + i\psi_i = ae^{i\theta}$, with the amplitudes slowly varying whereas the phases are rapidly varying and, in particular, distributed uniformly over the interval $[0;2\pi)$. However, one could expect that the phase dynamics can play a role in the self-organisation and the formation of coherent structures. In the same manner it is also expected that the RPA falls short to take coherent interaction between phases into account. In this work therefore, we studied the role of phase dynamics and the coupling of phases between different modes on the characteristic time evolution of the turbulent. We assume a simple turbulent system where the so-called stochastic oscillator model can be employed. The idea of interpreting turbulence by stochastic oscillators. The stochastic oscillator models can be derived from radical simplifications of the nonlinear terms in the Navier-Stokes or Gyro-Kinetic equations. In this particular case we adopt the basic equation for the stochastic oscillator model with passive advection and random forcing from Ref.