Turbulence and Sheared Flow in Fusion Plasmas: a Simple Fluid System

The operation of fusion reactors by magnetic confinement depends on a good understanding of the turbulent transport. It is known that shear flows are beneficial, as they can reduce or even suppress radial transport. However, evidence exists that if the flow is strongly sheared a new instability can arise. There is also evidence that differential flows can be generated by the plasma itself, reducing transport-the so-called zonal flows.
 
We use a simple system of fluid equations and extend to the nonlinear regime the linear results previously obtained. This system captures effects of the micro scales of the plasma in the form of the Ion Temperature Gradient and the Parallel Velocity Gradient instability and the effects of an external shear flow. Nonlinear analytical and numerical studies allowed to verify that the system contains zonal flows which reduce transport. An effect similar to the Dimits shift was observed. A reduction of transport by the action of an external shear flow was also observed.