Performance results on a C-SiC alloy coating chemically vapor-deposited onto graphite substrates

A new coating material was successfully tested in both the limiter and the beam armor tile positions in Doublet III, an experimental tokamak fusion device. The coating material is an alloy of about 10 wt.%SiC in pyrolytic carbon deposited onto graphite substrate tiles of sizes up to 10 cm X 10 cm X 2.5 cm. Performance of the coating on graphite tiles under conditions of localized thermal shock was also investigated in laboratory simulation studies using electron beam energy depositions at power densities greater than levels normally experienced in tokamak service. The results of the test are presented along with observations made during surface examination and microstructural evaluation of the coating. The coating features and deposition model are also described. In a review of related studies of the C-SiC alloy coating, emphasis is placed on the two key advantages, low atomic number and low chemical sputtering, offered by this coating for use on graphite substrates to achieve improved plasma performance in both present and next-generation fusion devices. (Auth.)