Parametric dependence of the edge radial electric field in the DIII-D tokamak

High spatially resolved measurements of the radial electric field, E r , have been made across the transition from L mode to H mode plasmas for many different plasma parameters and conditions. The evolution of the well-like structure of the E r profile formed at the L-H transition has been investigated. No distinct variation in the shape or width of the E r well at the L-H transition is observed as a function of the plasma parameters investigated, such as the plasma current, the toroidal magnetic field and the plasma density. The value of E r is negative just inside the last closed flux surface (LCFS) for all the plasmas studied. There is a variation in the depth of the E r well for different conditions. The experimental results have been compared with theoretical predictions for suppression of plasma turbulence by sheared E × B plasma flow.