In plasma source ion implantation (PSII), a target to be implanted is immersed in a weakly ionized plasma and pulsed to a high negative voltage. Plasma ions are accelerated toward the target and implanted in its surface. In this article, two factors in the analysis of these discharges are examined for the first time: (1) displacement current across the expanding sheath results in increased implant current and decreased implanted ion energy, with respect to existing models; and (2) ion depletion around the target due to high pulse repetition rates results in decreased implant current and dose. These effects are studied with analytic models and particle‐in‐cell simulations. Simulation results are compared to previously published PSII models.