Any discussion of impurity behavior during neutral-beam injection in ISX-B is best formulated in terms of the distinctive differences observed between ohmically heated, co-injection, and counter-injection discharges. In ohmically heated discharges both the production and the transport of impurities depend upon whether the working gas is hydrogen or deuterium. The influx of oxygen is almost the same for both cases, but the influx of metals is about a factor of 3 larger in the deuterium discharges. These results are consistent with the picture that oxygen gets into the plasma mainly through some process of chemical detachment, but that the metals are produced by neutral-particle sputtering at the walls. This conclusion pertains to discharges that are kept centered in the vacuum chamber so that the plasma limiter interactions are minimized. Under this condition the ion temperature near the edge of the current column is apparently low enough that charged particle sputtering of the limiter is a relatively small effect
