Molybdenum sources and transport in Alcator C-Mod

Abstract

We present a characterization of molybdenum sources, Γ Mo, core Mo content, N Mo, and their dependencies on Alcator C-Mod operational regimes. This includes sources from the divertor, the inner wall and the ICRF antenna limiters. We also present information characterizing the penetration of these impurities into the core plasma under different conditions based on penetration factors, PF= N Mo/ Γ Mo (s). In general, the inner wall Mo source is large (∼10 18 s −1) but is found to be relatively uncorrelated with the core Mo level in diverted plasmas. The outer divertor source is of similar order to that from the inner wall and has a penetration factor in the range 10 −5–2×10 −3 s depending on density and confinement mode. The antenna limiter Mo sources are typically smaller, but with higher penetration factors – 10 −3–2×10 −2 s. The behavior of the antenna limiter sources is consistent with physical sputtering due to the influence of RF sheath rectification.