Scrape-off layer profile modifications by convective cells

Convective cells (CC’s) are important in understanding density profile modifications induced by ion cyclotron range of frequencies (ICRF) antennas. This has motivated the present work in which the effect of CC’s on transport in the scrape-off layer is studied, in the regime where the density gradient scale length Ln and the cell size L are comparable. Monte Carlo simulations show that closed cell convection acts to flatten the density profile, and that open cells enhance the particle flow to the wall, depleting the density and yielding profiles similar to those measured near ICRF antennas. A new one-dimensional, two-branch model of CC transport is shown to agree well with the simulations. The model gives rise to two characteristic scale lengths, only one of which is retained in the enhanced diffusion models that are applicable for Ln≫L. The two-branch model is expected to be useful in analyzing ICRF experiments.