Vendredi 17 octobre à 11h00, salle des séminaires IRPHE
Abstract: Microscale turbulence nonlinearly organises through generation of secondary or tertiary mesoscopic structures such as zonal flows, fronts or staircases. Radial electric field evolution underpins these questions and is central to understanding the onset and sustainment of transport barriers. These barriers often arise following transport bifurcations, which are deemed essential to fusion performance. They occur spontaneously throughout the confined plasma and are especially relevant in the narrow, peripheral region of the plasma edge. This region however is especially challenging to model and to understand for it is home to large, concentrated shear and to steep gradients. As turbulent scales become comparable to free energy gradient scales, oft-assumed scale separations in turbulence models break down, promoting the use of more computationally-intensive ‘flux-driven’ frameworks. Sources (forcing) and boundary conditions play an important role as the plasma edge sits at the confluence of conflicting dynamics, notably outgoing heat and incoming particle fluxes from the boundaries.
We propose to review some of the key features above and discuss some of the basic features through which turbulence organises in a magnetised fusion plasmas. In paricular, we will highlight analogies with geophysical or astrophysical fluid dynamics and briefly touch upon the mechanisms and causality behind electric field and shear (vorticity) production.