Plasma interactions with mixed-matarial plasma facing components

The interactions of several types of mixed-materials with a bombarding deut erium plasma are described in this paper. The first type of mixed-material surface is a designed, or engineered, surface: a silicon-doped carbon-fiber composite (NS-31). The Si-doped CFC is compared to an identical, but undop ed CFC. The net erosion rate, which under these experimental conditions sho uld be dominated by chemical erosion, is reduced by an amount that is about the same as the concentration of the dopant material. Examination of the C FC surface shows that the dopant exists in macroscopic size zones and is no t uniformly distributed throughout the CFC. The addition of a more uniforml y distributed dopant, in this case beryllium deposited from the plasma on g raphite, is shown to reduce the chemical erosion by more than the concentra tion of the dopant in the surface layer. Finally, the concentration of impu rities in the plasma (and therefore the arrival rate of these impurities at the surface) is influential in determining the resultant chemical bonding on the surface. If the arrival rate of carbon at the surface is large, then a surface rich in carbon-carbon bonding develops. If the arrival rate of c arbon at the surface is reduced, then the carbon in the surface exhibits pr eferential carbidic bonding. At low carbon concentration, carbidic bonding is observed in the surface layer regardless of the temperature of the sampl e during the plasma exposure.