Erosion and deposition at the ALT-II limiter of TEXTOR

A new method for the determination of massive erosion and deposition on plasma facing components has been developed and was tested successfully on a graphite tile of the ALT-II limiter of TEXTOR. The surface profile of the tile was measured before and after exposure to plasma discharges with an optical profiler, erosion or deposition is determined from the difference of the two profiles. The profiles were determined relative to specially machined holes, which provide stable reference points. An accuracy of about 1 μm can be achieved. After exposure for 7625 plasma seconds a maximum erosion of 28 μm carbon is observed in erosion dominated areas, while a maximum deposition of about 40 μm is observed in net redeposition areas. The composition and structure of the redeposited layers were investigated with secondary ion mass spectroscopy and scanning electron microscopy.