A study of molybdenum influxes and transport in Alcator C-Mod

A characterization is presented of Mo sources Gamma (Mo), core Mo content N -Mo and their dependences on the Alcator C-Mod operational regimes. The pri mary impurity source locations are the divertor, the inner wall and the ICR F antenna limiters. Boronization is used to coat the first wall surfaces wi th a thin layer of B. which greatly reduces the Mo sources for a period of time, eroding away with an c folding period of 15-50 discharges. The penetr ation of Mo into the core plasma under different conditions is analysed usi ng the concept of penetration factor, PF = N-Mo/Gamma (Mo) (s). In general, the inner wall Mo source is large (similar to 10(18) s(-1)), but is found to be relatively uncorrelated with the core Mo content in diverted plasmas. The outer divertor source is of a similar order to that of the inner wall and has a penetration factor in the range 10(-5) x 10(-3) s depending on de nsity and confinement merle. The antenna, limiter Mo sources are typically smaller. but with higher penetration factors of 10(-3)-2 x 10(-2) s. The be haviour of the antenna limiter sources is consistent with physical sputteri ng due to the influence of RF sheath rectification. The measurements of the plasma potential on field lines connected to the antenna are very high whe n the antennas are energized, often reaching hundreds of volts.