Two-dimensional turbulence analysis using high-speed visible imaging in TJ-II edge plasmas

Transport in fusion devices is a phenomenon with high degree of complexity. Localized layers where Ex B shear stabilization mechanisms are likely playing a role, have extensively been proved to have a beneficial impact in confinement. A reduction in turbulence amplitude is expected and measured [1]. However few attempts have been made to study the effects of such layer on the morphology of turbulent structures [2]. Two-dimensional images of edge plasma turbulence have been obtained by high-speed imaging in the visible range in the edge of tokamak devices [3], [4]. This paper reports a 2-D visualization of transport in the plasma edge of TJ-II stellarator. A wavelet-based image analysis method is used to localize and characterize blob-like structures. The impact of shear flow and external biasing on turbulent structures is investigated by means of this method. (Author)