ION-TRANSPORT IN TURBULENT EDGE PLASMAS

Edge plasmas, such as the tokamak scrape-off layer, exist as a consequ ence of a balance between cross-field diffusion and parallel losses. T he former is usually anomalous, and is widely thought to be driven by strong electrostatic turbulence. It is shown that the anomalous diffus ion affects the parallel ion transport by giving rise to a new type of thermal force between different ion species. This force is parallel t o the magnetic field, but arises entirely because of perpendicular gra dients, and could be important for impurity retention in the tokamak d ivertor.