Erosion and redeposition observed in limiter experiments at TEXTOR

Erosion of Mo and W in the edge plasma of a TEXTOR-94 limiter tokamak was investigated for OH and NBI conditions. The measured penetration distances of neutral Mo into the plasma were small enough for ionized Mo to return back to the surface during the first gyration. A twin limiter half made of W and another half made of graphite was ideal to study prompt redeposition of W on the limiter surface. The surface of the limiter was modified by erosion and redeposition processes and exhibited particle recycle characteristics different from those of the original material. The limiter surface made of W-vacuum-plasma-spray coating showed substantial reduction of the W release rate by C coverage. Highlights of the experimental results obtained in high-Z limiter experiments at TEXTOR are summarized. (author)