München 2019 – wissenschaftliches Programm

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P: Fachverband Plasmaphysik

P 18: Postersitzung

P 18.66: Poster

Donnerstag, 21. März 2019, 16:30–18:30, Foyer Audimax

Three-mode coupling under imposed E× B shear — •Til Ullmann¹, Bernhard Schmid¹, Peter Manz², and Mirko Ramisch¹ — ¹Institute of Interfacial Process Engineering and Plasma Technology, University of Stuttgart — ²IPP, Max-Planck Institut, Garching

In toroidal fusion plasmas, shear flows are considered to be involved in the reduction of turbulent transport. Background shear flows can tilt the vortex structure of the perturbed plasma, which leads to a higher Reynolds stress. A stronger tilt of the eddies enhances a straining out process, which favours the creation of large scale zonal flows. Therefore, zonal flows act as an energy sink for turbulence. At the stellarator TJ-K the influence of the equilibrium shear flow on turbulence is investigated experimentally. The equilibrium shear is changed with plasma biasing and diagnosed with an emissive probe. In TJ-K, turbulence is dominated by drift-wave dynamics. Their nonlinear behavior can be described by three wave coupling: k₁+k₂=k₃, ω₁+ω₂=ω₃. In order to account for both resonance conditions, a wavenumber-frequency bicoherence spectrum is calculated from potential fluctuations measured with a 128 pin poloidal probe array. Increased non-linear mode coupling is observed for (k₃,ω₃) following the drift-waves’ dispersion relation. The influence of background shear flows on these three-wave interactions is studied and possible consequences for zonal-flow generation are discussed.