Steady-state convection and fluctuation-driven particle transport in theH-mode transition

Large-scale steady-state convection is found to dominate the particle transport just inside the last closed flux surface (LCFS) in Ohmic discharges in the CCT tokamak. Near the limiter radius and in the scrape-off layer, fluctuation-induced transport is prevalent. At the L-H transition, the convection pattern near the LCFS is disrupted and a more poloidally symmetric, near-sonic plasma flow develops. Convective and turbulent particle transport are reduced across the entire edge region, resulting in the formation of the H-mode edge transport barrier.