Journée de Dynamique Non Linéaire

10h30   Paul Terry (University of Wisconsin, USA)
Nonlinear damping of plasma zonal flows excited by inverse spectral transfer

11h35   Olivier Agullo (Dynamique des Systèmes Complexes, P.I.I.M.)
A study of alpha and beta effect in large scale dynamo

11h55   Philippe Ghendrih (D.R.F.C., C.E.A. Cadarache)
Long range transport in edge tokamak turbulence

Résumé du séminaire de Paul Terry

Plasma zonal flow excitation and saturation in a fluid model for trapped electron turbulence are studied spectrally. The zonal flow is a spectral condensation onto the anisotropic, large scale, zero frequency linear wave structure. In the representation diagonalizing the wave coupling that dominates interactions at long wavelengths, wave anisotropy greatly enhances nonlinear triad interactions involving zero frequency waves. This creates enhanced spectral energy transfer to zonal modes. Zonal modes are excited on both unstable and purely stable eigenmode branches. Coupling to the latter introduces robust, finite amplitude-induced damping of zonal flows, providing saturation of zonal flows and a significant saturation mechanism for the higher wavelength trapped electron turbulence.