Studies of Radial Electric Field Formation and Its Effect on Fluctuations and Transport Barriers in the JFT-2M Tokamak

The mechanism of E × B flow formation, the effect of the E × B flow on parallel flow, the reduction of fluctuations by the shearing effect of the E × B flow shear, and the relation between the geodesic acoustic mode (GAM) and density fluctuations are discussed based on the experiments using various E_r measurements in the JFT-2M tokamak. The experiments in plasmas with H-mode and counter-neutral beam injection (NBI) mode show that the feedback loop of the E × B flow shear, the fluctuation suppression, and an increase of ion diamagnetic flow are key to the formation of the transport barrier in toroidal plasmas. Two important effects of the radial electric field are presented: One is fluctuation suppression by the E × B flow shear, and the other is a drive of the parallel flow by radial electric field, which explains the driving mechanism of a spontaneous toroidal flow. The relation between the GAM and the density fluctuations is also discussed. The GAM is observed to be excited by the nonlinear coupling of density fluctuations, while the GAM itself affects the amplitude of the density fluctuations.