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(EX/C4-1Ra) Turbulence Regulation and Stabilization by Equilibrium and Zonal Flows

G.R. McKee1), R.J. Fonck1), M. Jakubowski1), K.H. Burrell2), T.N. Carlstrom2), C. Fenzi1*), R.J. Groebner2), K. Hallatschek3), R.A. Moyer4), W. Nevins5), T.L. Rhodes6), C. Rost7), D. Rudakov4), X. Xu5)
 
1) University of Wisconsin, Madison, Madison, USA
2) General Atomics, San Diego, California, USA
3) Max Planck Institut fur Plasmaphysik, Garching, Germany
4) University of California, San Diego, La Jolla, California, USA
5) Lawrence Livermore National Laboratory, Livermore, California, USA
6) University of California, Los Angeles, Los Angeles, California, USA
7) Massachusetts Institute of Technology, Cambridge, Massachusetts, USA
* Present address: CEA, Cadarache, France

Abstract.  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$\scriptstyle \perp$ . $ \rho_{I}$ < 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. *Work supported by U.S. Department of Energy under Grants DE-FG03-96ER54373, DE-FG03 01ER54615, and Contracts DE-AC03-99ER54463 and W-7405-ENG-48.

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IAEA 2003