Low-Z impurities in the PLT Tokamak

Concentrations and influx rates of oxygen and carbon ions have been determined in a variety of discharges in the PLT Tokamak. Oxygen, and to a lesser extent carbon are found to affect strongly the plasma behavior, mostly by changes in resistivity. The principal effect appears to be peripheral cooling by oxygen radiation, which changes the radial distribution of current density and temperature, and simultaneously inhibits the influx of high-Z limiter and wall material. (author)