Neutralization of the positive ion space charge between the grids of a positively charged‐ion accelerator by injecting negative charges into this region has been studied theoretically. The current density of a beam of charged particles being accelerated between two parallel plate electrodes can be increased substantially by this injection. Multiple beams of oppositely charged particles can be used to produce the most substantial increases in the current density of the primary beam. The current density of this beam increases monotomically with the number of optimally selected, injected particle beams being used. There is an optimum injected particle current density and energy associated with each beam that yields the maximum extracted beam current density for a given number of injection stages. The total required injected particle current density, regardless of the number of stages used, is of the order of the ion current density times the square root of the extracted ion‐to‐injected particle mass ratio.