On the nature of radial transport across sheared zonal flows in electrostaticion-temperature-gradient gyrokinetic tokamak plasma turbulence

摘要

It is argued that the usual understanding of the suppression of radial turbulent transport across asheared zonal flow based on a reduction in effective transport coefficients is, by itself, incomplete.By means of toroidal gyrokinetic simulations of electrostatic, ion-temperature-gradient turbulence,it is found instead that the character of the radial transport is altered fundamentally by the presenceof a sheared zonal flow, changing from diffusive to anticorrelated and subdiffusive. Furthermore, ifthe flows are self-consistently driven by the turbulence via the Reynolds stresses (in contrast tobeing induced externally), radial transport becomes non-Gaussian as well. These results warrant areevaluation of the traditional description of radial transport across sheared flows in tokamaks viaeffective transport coefficients, suggesting that such description is oversimplified and poorlycaptures the underlying dynamics, which may in turn compromise its predictive capabilities.