Thermionically emitted primary beam (usually Cesium).
A beam sputter simulation is shown in the following plots. The first plot is the primary beam which is emitted thermionically from the ring-shaped electrode. The beam is computed to the target, which is the sputter ion source. The space charge densities are saved (with the sign reversed) and are restored for the secondary run of the sputtered beam. The emission current density distribution is proportional to the space-charge density of the primary beam at the target. A cosine distribution of current is injected from each point along the target for the secondary run of the sputtered current.
Sputtered beam from target (usually a negatively charged heavy metal).