Performance enhancement of a compact radio frequency ion source by the injection of supplemental electrons

A versatile, high brightness, volume type, RF source, capable of producing positive ion beams with intensities as high as 1 mA from gaseous feed materials and microamperes of negative ion beams has been characterized. The source can also be operated as a plasma sputter negative ion source to generate up to 1 mA of a selected species. The performance of the source in the positive and negative volume modes of operation can be greatly enhanced by addition of a removable, water cooled filament assembly in place of the negative sputter probe. For example, the material utilization efficiencies of gaseous feed species can be more than doubled, total current intensities increased up to 40%, N₂ molecular dissociation fractions increased by 20% and minimum operating pressures reduced by a factor of four when operated in the volume mode. These added electrons also favorably effect, as a consequence of lower pressures, the emittance apparently through a reduction of scattering in the beam through the transport system. A brief description of the source and performance data for the positive volume mode of operation will be presented