In a gridded ion source, DC or RF discharge are used to generate ions, which are then accelerated and decimated using grids and apertures. Here, the DC discharge current or the RF discharge power are used to control the beam current.
The ion current density  that can be accelerated using a gridded ion source is limited by the space charge effect, which is described by Child's law:
where  is the voltage between the grids,  is the distance between the grids, and  is the ion mass.
The grids are placed as closely as possible to increase the current density, typically . The ions used have a significant impact on the maximum ion beam current, since . Everything else being equal, the maximum ion beam current with krypton is only 69% the maximum ion current of an argon beam, and with xenon the ratio drops to 55%.