Surface loads and edge fast ion distribution for co- and counter-injection in ASDEX Upgrade

Abstract

The fast particle flux onto the material surfaces and the fast ion edge distribution are compared between ASDEX Upgrade H-mode and quiescent H-mode (QH-mode) in the presence of toroidal ripple and radial electric field Er by using the orbit-following Monte Carlo code ASCOT. So far, the QH-mode has been obtained only with counter-injection of the neutral beams. The wall load caused by co-injected beams in H-mode is small and without ripple it is negligible. With counter-injection (QH-mode case), the wall load is substantial even without the ripple. The ripple always increases the wall load, but the divertor load is either decreased or is unchanged. The effect of Er alone is small, but it boosts the ripple-trapping of beam particles near the location of its maximum absolute value on the horizontal midplane. The fast ion density and its gradient in the pedestal region are higher for counter-injected than for co-injected particles. The ripple decreases the density gradient in both the cases. To make a connection with the experiment, the flux of high-energy tritons from beam–plasma interactions onto the surfaces is evaluated. The simulated flux of tritons impinging on the material surfaces is in qualitative agreement with the measured tritium distribution on the wall and divertor.