EXB TRANSPORT IN THE DIII-D BOUNDARY PLASMA

We have measured the electrostatic turbulence and associated particle transport in the DIII-D boundary plasma using a fast reciprocating Langmuir probe array located on the outboard midplane. Both the normalized rms fluctuation levels (density and floating potential) and the fluctuation-driven particle transport are altered by the L-H transition in the SOL. At the separatrix, the density fluctuation level is reduced a factor of 2, consistent with reflectometry results. There is a corresponding decrease in the turbulent particle flux. Deeper in the SOL, the turbulent particle transport in H-mode exceeds the L-mode value. The perpendicular diffusion coefficient D(perpendicular-to) and particle confinement time tau(p) have been estimated, assuming that the transport is purely turbulent and uniform on a flux surface. We find D(perpendicular-to) = 0.7D(B) (L) and 0.04D(B) (ELM-free H), and tau(p) = 54 ms (L) and 480 ms (ELM-free H).