Low-energy extraction with simple two grid accelerator system

An experimental investigation for extending the ion extraction capabilities of a two grid accelerator system to low energy is described. The preliminary results have shown that low-energy ion beams ranging from 15 to 80 eV can be extracted by biasing the screen grid potential to be negative to the ground at small grid separation distance. The beam currents which have been extracted are 20--60 mA. Beam current densities ranging from 0.15 to 0.45 mA/cm2 with good uniformities are measured at a location 20 cm downstream of the grids. It is found that the extraction capabilities are mainly determined by the operation parameters of the ion source, but they can be substantially effected by changing the grid separation distance and the magnetic field geometry and strength in the discharge chamber