Power handling on castellated divertor components is an area of concern for ITER, in particular with respect to transient excursions by ELMs. Protection of leading edges from full parallel flux is realised by appropriate shaping on the cost of increased power load at plasma exposed surfaces. For insufficiently mitigated ELMs melting can still occur. Surface damage by repeated transient melting and its effects on plasma operation have been studied first in JET and recently in a companion experiment at ASDEX Upgrade. The latter experiment provided for the first time ELM resolved measurements of the thermionic emission current, which is assumed to be the main driver for melt motion by corresponding jxB forces. These measurements as well as results of first post-exposure surface analysis will be discussed.
[mehr]