Surface analysis of TFTR limiter tiles

The plasma contacting surfaces of the TFTR movable limiter consist of an array of titanium carbide coated graphite tiles. The surface characteristics of the graphite tiles were analyzed prior to installation to establish the initial limiter conditions, and after exposure to 800 Ohmically heated discharges in TFTR to provide data on the limiter conditioning process. Some tile surfaces showed nearly complete removal of the TiC surface as a result of plasma exposure. 3D and 2D elemental mapping of the tile near surface regions show deposition of vacuum vessel metals (primarily Ti and Ni) in the form of oxides.