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P: Fachverband Plasmaphysik

P 12: Magnetic Confinement - Poster

P 12.4: Poster

Dienstag, 6. März 2018, 16:15–18:15, Redoutensaal

Shearing rate dependence of Reynolds-Stress — •Til Ullmann, Mirko Ramisch, and Bernhard Schmid — Institut for Interfacial Process Engineering and Plasmatechnology - University of Stuttgart

Turbulence generated zonal flows (ZFs) are known to be part of regulating turbulent transport and, therefore, are suspected to be involved in spontaneous transitions from low to high confinement regimes in toroidal fusion plasmas. ZFs are driven by radial gradients of the turbulent Reynolds-Stress ⟨ v_θv_r ⟩, which de facto measures the tilt of vortices. Hence, equilibrium shear flows constitute a seed flow for initially tilting vortices, initiating the ZF drive and stimulating its selfamplification. In this contribution the dependence of Reynolds-Stress on background flow shearing rates is investigated experimentally. To this end, the poloidal E× B background flow in the sellarator TJ-K is controlled via plasma biasing. A ring shaped electrode is positioned in the plasma and set on a positive potential with respect to the vacuum vessel. This application even allows to equalize the pressure driven E× B background flow and, therefore, is found to be minimal. The trend of the Reynolds-Stress with the shearing rate will be analysed and compared to the development of the measured ZFs.