Nonlinear interaction and turbulence transition in the limiting regimes of plasma edge turbulence

Abstract

We study the nonlinear coupling mechanism and turbulent transition in magnetically confined plasma flows based on two representative limiting regime dynamics. The two-field flux-balanced Hasegawa–Wakatani (BHW) model is taken as a simplified approximation to the key physical processes in the energy-conserving nonlinear plasma flows. The limiting regimes separate the effects of finite non-adiabatic resistivity and extreme non-normal dynamics to enable a more detailed investigation on each individual aspect with the help of various mathematical tools. We adopt the strategy from the selective decay theory used for the simpler one-field system to develop new crucial a priori estimations in the two-field model framework. The competing effects from model dissipation, finite particle resistivity, as well as the nonlinear interaction with a zonal mean state to induce dual direction energy transports are characterized from the systematic analysis. Non-normal dynamics with aligned eigendirections is also shown to go through a sharp transition from turbulence to regularized zonal flows. The diverse phenomena implied from the limiting regime analysis are further confirmed from direct numerical simulations of the BHW model.