Transport of edge-localized mode energy in a scrape-off layer in the presence of collisionless fast electrons

The transport of the energy delivered by an edge-localized mode (ELM) into the scrape-off layer (SOL) of a tokamak plasma is studied with particle-in-cell simulations. A simple one-dimensional model with a Monte-Carlo procedure for Coulomb collisions is used. The SOL is collisional before the ELM, but the mean-free-path length in the hot ELM plasma is longer than the connection length, such that fast electrons can travel directly from the midplane to the target plate. However, the sheath potential increases rapidly, and most of the energy is transported with a velocity of order of the ion sound speed if secondary electron emission (SEE) is absent or weak. In the case of strong SEE, though, a large fraction of the energy can be carried by fast electrons during the ELM pulse.