ausblenden:
Schlagwörter:
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Zusammenfassung:
Turbulence flows are directly measured in a tokamak plasma by applying time-delay-estimation (TDE) analysis to localized 2-D density fluctuation
measurements obtained with Beam Emission Spectroscopy on DIII-D. The equilibrium radial flow shear near the plasma edge (0.8 < r/a < 1) varies strongly with
magnetic geometry. With the ion grad-B drift directed towards the X-point in a single null plasma, a large radial shear in the poloidal flow is measured, while little
shear is observed in the reverse condition. This large shear appears to facilitate the L-to H-mode transition, consistent with the significantly lower LH transition
power threshold in this configuration. In addition, time varying, radially localized (k . ρI < 1) flows with a semi-coherent structure peaked near 15 KHz and a
very long poloidal wavelength, possibly m=0, are observed. These characteristics are very similar to theoretically predicted zonal flows that are self-generated by
and in turn regulate the turbulence.
