EDGE PHYSICS IN REVERSED-FIELD PINCH AND TOKAMAK - SIMILARITIES AND DIFFERENCES

The edge-region properties of a reverse-field pinch (RFP) configuratio n are reviewed and a comparison with those of tokamaks is attempted. D espite the different magnetic configurations, many similarities have b een observed. Among the similarities is the electrostatic nature of th e particle transport and the structure of the plasma potential. In par ticular the radial electric field changes sign across the last closed flux surface and gives rise to an E x B velocity shear layer. The anom alous transport driven by electrostatic and magnetic fluctuations is a ddressed and the regimes of improved confinement recently observed in RFPs are reviewed. The role of the velocity shear on turbulence stabil ization in these regimes is discussed.