Bulk-boronized graphite (20% boron) has been tested as a limiter material in the Wendelstein 7-AS stellarator. The recycling behaviour and the plasma impurities are compared for the new material and the formerly used TiC-coated graphite with stainless steel and boronized walls. After conditioning the recycling and the oxygen and carbon levels are comparable for both materials. No significant impact of sputter boronization from the limiters on the oxygen level was observed. A drastical reduction of oxygen by about a factor of 10 was obtained only after additional gas boronization. In this case Z[sub eff] is primarily determined by carbon and boron. For ECF standard discharges Z[sub eff][approx equal]2 with P[sub rad]=6% of the input power was found as compared to Z[sub eff]< or approx.3 and P[sub rad]=10% before boronization and Z[sub eff][approx equal]4, P[sub rad]=20% with TiC-limiters. (orig.).
Brakel, R; Burhenn, R; Behrisch, R; Grigull, P; Hacker, H; Hildebrandt, D; Hofmann, J V; Mahn, C; Roth, J; Schneider, U; Weller, A;  Hirooka, Y;  W7-AS Team; NI Group; ECRH Group
- Max-Planck-Inst. fuer Plasmaphysik, Garching (Germany)
- Inst. of Plasma Physics and Fusion Research, Univ. California, Los Angeles, CA (United States)