Collisional transport near the separatrix of a tokamak and the H-mode

The collisional transport of electrons and ions in the scrape-off layer just outside the magnetic separatrix of a diverted tokamak plasma is investigated. This extends previous work by Hinton, which focused on ion transport alone and which correctly interpreted the H-mode power threshold dependence on the ion grad-B drift direction. The presence of a plasma pinch effect driven by a poloidal electron temperature gradient is predicted. This inward convection can make a significant contribution to the energy and particle confinement. The strength of this effect is computed using a simple model and DIII-D data.