Interaction between ion source plasma and ion source wall

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Condition of the wall largely affects the performance of an ion source. Several fundamental mechanisms are responsible for the change in extractable amount of ions from the source. These include change of particle/energy reflection coefficient at the source wall due to formation of deposition layers, and alteration of dc electromagnetic structures near the source wall. Time-of-flight energy analysis for neutral particles, optical emission spectroscopy, and electrostatic probes were the three major tools employed to investigate factors governing the plasma-surface interactions in ion source plasmas. Peaks of velocity distribution functions of neutrals effusing out of plasma, shift toward the higher energy side with the increasing discharge power into the ion source. Vacuum ultraviolet spectra of hydrogen gas in a negative hydrogen ion source have shown the coverage of high temperature cathode materials alters distributions of molecular excitation levels of the gas confined in the ion so … More urce. High frequency electrical powers can excite plasma without any cathodes acting as sputtering/evaporation particle sources, but they still form deposition layers on ion source walls. The deposition layers formed by high frequency discharge power often show insulating characteristics causing change in local potential distributions around the ion extraction holes. The penetration of local electrical potential into plasma has been measured with the extraction potential turned on. The result has clearly shown the presence of field attracting ions to be extracted from the source. The extraction probability calculated from the local electric field has been compared with the experimental result. Plasma flow speed which is an input parameter for the theoretical model to predict extraction probability has been measured experimentally by dc laser photodetachment method. Other diagnostic methods to characterize plasma surface interaction like laser induced photoelectron emission have been developed to further deepen the understanding the plasma-surface interaction for ion source and process plasmas. Less