Impurity Sources And Accumulation In Ohmically Heated Isx-B Discharges

Spectroscopic observations on the ISX-$B$ (impurity study experiment) tokamak indicate that most of the metallic impurities come from the wall in Ohmically heated discharges in which the plasma is kept centered in the vacuum chamber. These impurities appear to accumulate during the quasi-steady-state part of the discharge if the working gas is deuterium but not if it is hydrogen.