Wall intersection of ion orbits induced by fast transport of pedestal plasma over an electrostatic potential hill in a tokamak plasma edge

An edge localized mode (ELM) event is known to transport a significant portion of pedestal plasma across the separatrix, and increase the divertor heat load to a possibly intolerable level in a tokamak fusion reactor. In the present work, a large random-walk transport is introduced in a plasma edge in a guiding center orbit following code XGC [C.S. Chang, S.H. Ku, H. Weitzner, Phys. Plasmas {\bf 11}, 2649 (2004)] to understand the effect of the shear in the edge radial electric field $E_r$ on the wall intersection location of the large-transport orbits. It is found that without an edge $E_r$, majority of large-diffusion induced ion orbital loss is to the outer divertor near the separatrix surface. However, with a large negative $E_r$ in the plasma edge with the ion grad-B drift into the single null divertor, ion orbits with their kinetic energy less than the potential energy shift their wall- intersection locations to the inner divertor while those with their kinetic energy higher than the potential energy retain their wall-intersections at the outer divertor. If the ion grad-B is away from the single-null divertor, the ion orbital loss is always to the outer wall.