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P: Fachverband Plasmaphysik

P 20: Hauptvorträge Lauber, Krämer-Flecken

P 20.2: Hauptvortrag

Donnerstag, 2. April 2009, 11:40–12:10, HS Biochemie (groß)

Overview on turbulence generated zonal flow shear — •Andreas Krämer-Flecken — IEF-4,Forschungszentrum Jülich, 53425 Jülich, Germany

It is a well accepted conception that small scale turbulent structures can form large scale coherent structures (e.g. zonal flows) via an inverse energy cascade. Examples of inverse energy cascades which lead to the generation of zonal flows can be found in the earth atmosphere, the oceans, planets and in numerous laboratory experiments. The zonal flows create transport barriers and influence the confinement. In plasma physics zonal flows play a crucial role in the regulation of anomalous transport. They are supposed to be the key for a better understanding of transport properties and a starting point for better control of particle- and energy transport with the aim to improve plasma scenarios for future devices as ITER.

Zonal flows are supposed to be generated by Reynolds stresses which itself are produced by drift waves, which can be treated as short lived eddies. The generated shear flow is retroactive on the background turbulence by reducing the eddy lifetime. Compared to the timescale of the turbulence zonal flows vary on a slow timescale.

Beside mean zonal flows the radial decrease of the magnetic field in fusion plasmas causes a nonuniform E× B flow which produces pressure asymmetries the geodesic acoustic mode. This mode appears at the plasma edge and is studied in large detail on different fusion devices amongst them at TEXTOR. The properties of the mode are discussed and the generation mechanism.