Session 7F - DIII-D: Edge and H-Mode.
ORAL session, Thursday morning, November 14
Vail Room, Adam's Mark
If in-vessel components in a magnetic fusion device are made of more than one materials, materials mixing will be unavoidable due to plasma-induced erosion and redeposition. This materials mixing alters surface characteristics, which can then affect the wall lifetime as well as edge plasma interactions. Related to such materials mixing, we have observed an interesting phenomenon in the recent PISCES-B Mod experiments that under deuterium plasma bombardment beryllium tends to be deposited with carbon impurities, a phenomenon referred to as "carbon poisoning"[1]. Importantly, carbon poisoning reduces beryllium erosion significantly. Recently, a similar phenomenon has been observed in JET where beryllium and carbon are used for in-vessel components[2]. First-order modeling on carbon poisoning has been carried out successfully and the mechanism is explained as carbon impurity trapping followed by thermally activated mixing with beryllium via inter-diffusion. Consistent with this model, experimental data indicate that carbon poisoning occurs only at elevated temperatures. In the present work, this model has been used to analyze materials dynamic compatibilities under DT-plasma bombardment for a variety of impurity-surface combinations that are relevant to existing fusion experiments and also future reactor designs. These combinations include: lithium, beryllium, boron, and carbon as the impurities and carbon, vanadium, molybdenum, and tungsten as the surface materials. [1] Y. Hirooka et al. J.Nucl.Mater. 230(1996)173. [2] H. Guo et al. Presented at the 12th PSI-Conf. St.Raphael (1996).