Self-consistent dynamics of interchange mode turbulence with large-scale flows
Department of Astronomy and Space Physics, Uppsala University, Sweden
The theory of zonal flows generation by Reynolds stress is extended by flute (interchange) mode turbulence. The specific role of density fluctuations and finite Larmor radius effects is clarified. To describe the dynamics of a large-scale plasma flow that varies on a longer time scale compared to the small-scale fluctuations, a multiple scale expansion is employed, assuming that there is a sufficient spectral gap separating large-scale and small-scale motions. The evolution equations for mean flow generation with sources consisting of the standard and diamagnetic (due to the density fluctuations) Reynolds stresses are obtained by averaging the model equations over fast small scales. Analysis of these equations shows that a disbalance between standard and diamagnetic Reynolds stresses is required for the flow generation.
Wave kinetic equation is formulated and structure of an appropriate adiabatic invariant for small scale turbulence in the presence of a mean flow is determined. The invariant corresponds to the quantities that are conserved as integrals over the small-scale part of the spectrum alone. The condition for growth of zonal flow due to the resonant interaction with wave turbulence is obtained.