Turbulence drive and causal generation of vorticity in edge fusion plasmas.

Abstract

The edge of fusion plasmas is particularly important to model as this is where the plasma self-organizes to higher-energy states. From a turbulence point of view, it is a difficult region to model, often marginally stable, possibly deviating from a quasilinear approximation and subject to the influence of the material boundaries. A "transport shortfall", i.e., an underprediction of turbulence transport, has often been reported at the plasma edge. The integration of core, edge and scrape-off layer (SOL) dynamics is an area of active investigation. We have recently provided evidence for an active interplay between the confined plasma and its material boundaries. This interplay (i) cures the 'transport shortfall' at the edge of the plasma column and leads to (ii) the onset of a spontaneous, albeit moderate, transport barrier at the plasma edge, the mechanisms of which have been studied in detail. The present paper is the companion manuscript to [Dif-Pradalier, G., et al. Commun Phys 5, 229 (2022) Dif-Pradalier et al. (2022)]. We provide here comprehensive details of the techniques and procedures used in the earlier paper, including the detailed linear stability of the plasma edge, nonlinear analysis for edge turbulence, the importance of forcing and boundary conditions, and further details of the method by which causality was assessed. It also highlights the central role of diamagnetic flows in the generation of the edge transport barrier.