The Dynamics of Small - Scale Turbulence - Driven FlowsM

We investigate the dynamics of small-scale turbulence-driven sheared E B ows in nonlinear gyroouid simulations. The importance of these zonal ows in the regulation of the turbulence was shown in our early simulations 1{3 and has been widely connrmed. Most of these ows experience fast collisionless linear damping, but there is a residual non-Maxwellian component of the ow which is undamped 4 and scales with r=R. In our original treatment, we included collisionless damping terms which capture the fast collisionless damping of the damped components, but which do not accommodate the linearly undamped components. Here, we modify the gyroouid closures to account for PPrsch-Schl uter heat ows. This modiication allows a linearly undamped component of the E B ows, and here we begin to assess its importance in nonlinear simulations. Our preliminary results indicate very near marginal stability zero-ux states can exist where the undamped zonal ows completely damp the turbulence, as shown in Ref. 5. But away from marginal stability, we nd that retaining the undamped component of the ow has very little eeect.