Influence of Electrode Structure on Ion Beam Extraction in Cold-Cathode Ion Source

In this study, we investigated the influence of the electrode structure on ion beam extraction in a cold-cathode ion source. Numerical simulations were performed for three typical structures of cold-cathode ion sources with different cathode and anode geometries using in-house 2-D ion ray-tracing code. We found that the potential structure inside the plasma source, which is greatly influenced by the electrode structure, plays a significant role in determining the amount and divergence of the extracted ion beam. The electrode structure influences the potential structure inside the plasma source and forms a radial electric field between the sheath edge and the extraction aperture. The radial electric field guides the ion beam to focus or diverge in this region, thus changing the characteristics of the ion beam extracted from the aperture. The simulation results reveal that the ion source with the cylindrical anode geometry extracts a higher current than those with other geometries due to its potential structure, which focuses the ion beam more efficiently. The simulation results are consistent with those of our experiments with a small-sized cold-cathode ion source.