Hannover 2010 – wissenschaftliches Programm

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P: Fachverband Plasmaphysik

P 5: Theory/Modelling I

P 5.4: Vortrag

Dienstag, 9. März 2010, 15:10–15:25, B 302

Derivation of a Reynolds stress response functional for zonal flows from numerical studies — •Niels Guertler and Klaus Hallatschek — Max-Planck-Institut für Plasmaphysik, Garching b. M., Germany

Numerical self-consistent ITG-turbulence studies, using the NLET code, show a Reynolds stress driven zonal flow pattern with a characteristic radial scale length. The level of turbulence is affected by both the intensity and the radial structure of the zonal flows. At the same time, the zonal flows are governed by the turbulence generated stress pattern. A feedback loop between turbulence and zonal flows results, which sets up a nearly stationary flow pattern in balance with turbulence. Turbulent states modified with artificial initial flow profiles do always decay into the self-consistent zonal flow pattern and demonstrate the intrinsic nature of its radial scale length and the robustness of the mechanism. Based on wave-kinetic theories, a response functional of the observed flows can be created, which reproduces the stress quantitatively albeit fails to predict the intrinsic flow pattern and its radial scale length. We use synthetic flows to validate and parameterize the analytic nonlinear relationship between the stress and the resulting flow and turbulence levels. The objective is to merge the observed relationships with the stress-flow response functional derived from wave-kinetic models to incorporate the radial scale length and predict the long-term behavior of zonal flows including the experimentally observed turbulence bifurcations, with obvious confinement optimization implications.