Plasma-induced damage of tungsten coatings on graphite limiters

Vaccum plasma sprayed tungsten coatings with an evaporated sandwich Re–W interlayer on graphite limiter blocks were studied after the experimental campaign in the TEXTOR tokamak. The coating morphology was modified by high-heat loads and co-deposition of species from the plasma. Co-deposits contained fuel species, carbon, boron and silicon. X-ray diffractometer phase analysis indicated the coexistence of metallic tungsten and its carbides (WC and W 2 C) and boride (W 2 B). In the Re–W layer the presence of carbon was detected in a several micrometres thick zone. In the overheated part of the limiter, the Re–W layer was transformed into a sigma phase.