Influx and sources of medium- and high-Z intrinsic impurities in the alcator C tokamak

The influx of heavy impurities in the Alcator C tokamak is determined as a function of plasma parameters from observations of intrinsic impurities, in conjunction with an empirically derived anomalous impurity diffusion model. The influx of molybdenum as a function of electron density is found to decrease dramatically as the electron density is raised above 1 × 1014 cm−3. Sputtering (by neutrals, ions and impurities) is probably the dominant molybdenum release mechanism in Ohmically heated discharges.