Edge turbulence and SOL transport in tokamaks

Some key topics in tokamak edge plasma transport and turbulence are reviewed. Multi-device results reveal a new paradigm of scrape-off layer (SOL) transport. Radial transport is driven by intermittency throughout the SOL, in between edge localized modes (ELMs) in H-mode, and comprised of plasma filaments that are generated near the last closed flux surface likely by interchange instability. The filaments travel radially at speeds of similar to 1 km/s into the SOL and have a poloidal size of 1-3 cm in most devices. The radial transport in the SOL is poloidally asymmetric, by factors of 2-5, causing a pressure peak in the low field side. This asymmetry and other neo-classical terms, such as Pfirsch-Schluter currents, are found to drive strong SOL flows. The intermittent particle flux, is 20% of the total, including ELMs, at low collisionality. becoming 70% of total at high collisionality. Numerical and analytical models can reproduce the scaling of intermittency with collisionality as well as many details of the filament dynamics in the SOL. (C) 2009 Elsevier B.V. All rights reserved.