Time-Dependent Measurements of Metal Impurity Densities in a Tokamak Discharge by Use of Laser-Induced Fluorescence

Measured Fe i densities in the edge region of the impurity study experiment (ISX-$B$) tokamak in Ohmic and neutral-beam-heated discharges are consistent with calculated densities, if one assumes that sputtering of the stainless-steel walls by charge-exchange neutrals is the dominant production mechanism. Fe i and Ti i densities observed during plasma shift experiments indicate that the limiters play only a minor role in impurity production in ${\mathrm{D}}_2$ discharges. This also suggests that most metals are sputtered from the walls.