Turbulent generation of poloidal asymmetries of the electric potential in a tokamak

Donnel, P.*; Garbet, X.*; Sarazin, Y.*; Asahi, Yuichi   ; Wilczynski, F.*; Caschera, E.*; Dif-Pradalier, G.*; Ghendrih, P.*; Gillot, C.*

Poloidal asymmetries of the plasma flow are known to play a role in neoclassical transport. According to conventional neoclassical theory, the level of poloidal asymmetry of the electric potential is expected to be very small. In the present work, a general framework for the generation of axisymmetric structures of potential by turbulence is presented. Zonal flows, geodesic acoustic modes and convective cells are described by a single model. This is done by solving the gyrokinetic equation coupled to the quasi-neutrality equation. This calculation provides a predictive calculation of the frequency spectrum of flows given a specified forcing due to turbulence. It also shows that the dominant mechanism comes from zonal flow compression at intermediate frequencies, while ballooning of the turbulence Reynolds stress appears to be the main drive at low frequency.