Monte Carlo simulations of the heat load asymmetries on JET divertor plates

Abstract

JET divertor load measurements using embeddedthermocouples have indicated a large inner/outer target loadasymmetry and a significant non-uniformity in the load to theouter target. Furthermore, under H-mode conditions, the loadappears to be dominated by the ion component. While theinner/outer target load asymmetry can be understood in terms ofthe conventional fluid picture, the sharp structures in thedeposition profile as well as the ion dominance of the load cannot be readily explained by the fluid approach. The guiding-centreorbit-following Monte Carlo code ASCOT is used to simulate the ioncontribution to the target deposition profiles, and this is thefirst time a narrow structure in the divertor loads has beenreproduced in simulations. The importance of the plasma edgecollisionality, the atomic, molecular and ionic collisions in thescrape-off layer, and the radial electric field both inside andoutside the separatrix are all studied individually in detail.