EFFECT OF IMPURITIES ON THE EROSION BEHAVIOR OF BERYLLIUM UNDER STEADY-STATE DEUTERIUM PLASMA BOMBARDMENT (VOL 228, PG 148, 1996)

As a candidate plasma-facing material for ITER (International Thermonu clear Experimental Reactor), beryllium has been evaluated with respect to deuterium plasma erosion characteristics using the PISCES-B Mod fa cility at ion fluxes around 5 x 10(21) ions s(-1) m(2) in the ion bomb arding energy range from 100 to 300 eV. It is found that at elevated t emperatures beryllium tends to be contaminated with trace amounts of p lasma impurities such as carbon, hydrocarbon, oxygen and nitrogen even under the energetic deuterium plasma bombardment. Among these plasma impurities, carbon and hydrocarbon are observed to form thin films. Th is carbon deposition effect has made it difficult to interpret the wei ght loss data in evaluating the erosion yield. A first-order model has been developed to account for the dynamics of this carbon deposition process and it has been suggested that some surface chemistry effect p lays an important role. This surface chemistry effect has been experim entally proved from the observation that carbon deposition can be avoi ded only at room temperature. Without impurity deposition, the berylli um surface after plasma bombardment is found to be cleaner in oxygen c ontent and smoother in surface topography than the as-received materia l. Interestingly, however, even without carbon deposition, the erosion yield data still tend to agree with beryllium oxide data.