Turbulence, flows and edge localized mode (ELM) dynamics in limiter H-mode plasmas in TEXTOR

The turbulence, plasma flow and edge localized mode (ELM) dynamics in the limiter H-mode TEXTOR plasmas are investigated. Properties of both ambient turbulence within 0 < k(perpendicular to) < 4.2 cm(-1) and coherent modes are studied on the ELM time scale in detail. The turbulence level near the pedestal is shown to evolve several times with the period of ELMs. Within the inter-ELM period the 'silent stage' is found which is characterized by an extremely low(below that for Ohmic plasmas) turbulence level and a phase growth in the reflectometry signal. The silent stage is associated with the quasi-steady state when the pedestal is formed and confinement is improved between two successive ELMs. Quasi-coherent density oscillations near the pedestal region with m approximate to 3, 5, 16 and 38 are measured with correlation reflectometry. Low-m modes are found to reveal the signatures of precursor mode. At first, the radial structure of the rotation shear and radial electric field E-r in limiter H-mode in TEXTOR is presented. The characteristic negative electric field well with the sharp gradient del E-r approximate to 250 V cm(-2) at approximate to 2 cm inside separatrix is resolved. The E-r x B rotation profile defines both the resulting plasma rotation in the electron diamagnetic drift direction and a significant rotation shear near the separatrix which exceeds the decorrelation rate of ambient turbulence by several times.