A Coupled Model Of Transport, Turbulence, And Mesoscale Flows
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A coupled model of transport, turbulence, and mesoscale flows is proposed, including turbulence spreading. The model consists of transport equations for plasma density and pressure coupled to a shell model of drift wave turbulence, which incorporates coupling to mesoscale flows via disparate scale interactions. The model can describe the turbulent cascade and its dynamical interplay with zonal and mean shear flows as well as the profile evolution (including the profiles of turbulence intensity itself) due to these self-consistent turbulent fluxes. This simple system of equations is shown to capture the low to high confinement (L-H) transition. It is also observed that as the heating is increased, the system goes through an intermediate…show more content… For instance the models including the effect of evolution of plasma turbulence driven by profile gradients were proposed and studied by various authors (see, e.g., Refs. 7 and 18). In particular, the model of Miki et al.7,19,20 has the advantage of including oscillations between two predators (zonal flows and mean flows) and one prey (turbulence) while achieving the L-H transition. As such, it is also able to describe an L-I-H transition (L-H transition with an intermediate phase), which was initially predicted by a 0D model.21,22 However in most of the reduced models, the transport coefficients are determined by an ad hoc shear suppression rule. Here we propose an approach based on shell models, where the shear suppression and the predator-prey dynamics are natural results of the disparate scale interactions incorporated within the shell model description.
The model that is introduced in this paper is interesting for various reasons. It is significant, for instance, in that it makes use of a simple description of turbulence based on shell models, yet it is able to describe the complex interplay between turbulence and zonal flows in a natural self-consistent way, without making use of ad hoc steady-state relations such as the shear suppression rule. On the other hand, the model