Experimental investigation on the poloidal extent of the turbulent radial flux in tokamak scrape-off layer

A consistent description of scrape-off layer transport is built from multi-diagnostic observations in ohmic discharges in Tore Supra. Fast imaging reveals the existence of relatively large filamentary structures on the low field side but not on the high field side of the torus. These filaments can exist either on open or closed magnetic flux surfaces and have a finite parallel extent from the outboard midplane. Probe electrostatic turbulence measured at the top of the plasma corresponds to the ExB convection of density burst, understood as the signature of filament propagation. Independent experiments on time-averaged parallel flows measured with a Mach probe lead to a poloidal mapping of the strongly asymmetric radial flux. This flux is centered at the outboard midplane and its poloidal half width is about 50 deg. The local turbulent flux on the top is consistent with the mapping.