Tungsten erosion at the ICRH limiters in ASDEX upgrade

All limiters on the low field side of ASDEX Upgrade are equipped with tungsten coated tiles. The W influx from the limiters was measured with a new spectroscopic setup providing sufficient time resolution to resolve the influx peak during edge localised modes (ELM). The ELM peak is mainly due to an increase of the mean ion energy hitting the W-surface. W influx due to sputtering by fast D+ ions from neutral beam injection was measured for different injection angles and compared to Monte Carlo calculations of the fast ion loss. The erosion depends less strongly on the injection angle than predicted by the code due to an enhancement of the fast ion transport by ELMs. At the antenna limiters of the ion cyclotron resonance heating (ICRH), the influx rapidly increases when the ICRH is switched on, which can be explained by a rise of the average sheath potential at the limiter. (c) 2007 Elsevier B.V. All rights reserved.