Anomalous particle transport and flow shear in the edge region of RFP's

The effect of the E x B velocity shear on the particle flux carried by electrostatic fluctuations at the edge is discussed comparing the results of the experiments T2R (R = 1.2 m, a = 0.18 m) and RFX (R = 2 m, a = 0.5 m). In both experiments electrostatic turbulence accounts for most of the particle flux. The shear of the E x B velocity is close or larger than the value required for turbulence suppression or reduction. Particle fluxes exhibit bursts which carry a large fraction of the total particle flux, and which tend to cluster during magnetic relaxation phase. On the average a Bohm estimate of the experimental plasma diffusivity accounts for the experimental data. Finally a discussion on the methods for turbulence control is given. (C) 2003 Elsevier Science B.V. All rights reserved.