Measurement of sheared flows in the edge plasma of the CASTOR tokamak

The ion saturation current and floating potential are measured with high temporal (1 µs) and spatial (2.5 mm) resolutions at the plasma edge of the CASTOR tokamak by two poloidally spaced radial arrays of Langmuir probes. The radial electric field and the phase velocity of plasma fluctuations are estimated. The position of the velocity shear layer (VSL) is localized with a high precision. The shearing rate ω _{E × B} determined and found to be comparable with the inverse of the correlation time of fluctuations 1/τ_ac outside the VSL and about five times higher in the proximity of the VSL. A small impact of the shear on fluctuation level at the VSL is observed also in the statistic parameters of the U _fl and I _sat.