Flux-balanced two-field plasma edge turbulence in a channel geometry

We investigate the drift wave-zonal flow interaction formulated on a channel domain geometry approximating an isolated plasma edge region with zero net radial transport across the boundary. The recent two-field flux-balanced Hasegawa-Wakatani (BHW) model with improved treatment for a parallel electron response is adapted to the channel geometry configuration, which allows for generalized non-uniform zonal density profiles and is valid for the simulation of turbulent fields near the tokamak or stellarator edge regions. New conserved quantities are constructed based on the channel geometry to help the analysis for the competition between zonal states and non-zonal fluctuations. Effective bounds can be found constraining the maximum growth of total fluctuations and the amplitude of the dominant zonal state based on the conserved quantities. Total statistical variance among all the modes can also be estimated depending on the zonal state strength. The theoretical discoveries are confirmed by detailed numerical experiments from simulations in the channel domain. In addition, the channel geometry provides further support for the important advantage of adopting the balanced flux correction in the BHW model by showing a physically consistent growth rate from a stability analysis for the small-amplitude fluctuation interaction with a prescribed zonal mean profile, in comparison with the persistent instability and strong outward transport found in the modified Hasegawa-Wakatani model even with the increasing zonal density profile. This is again confirmed by direct numerical simulations of the two models. The channel domain BHW model framework with attractive features implies many potential applications in the study of the complex phenomena in plasma edge turbulence.