Space-Charge Expansion of a Positive Hydrogen Ion Beam Leaving a Duoplasmatron Ion Source

Space-charge is shown to be the controlling influence in the expansion of a positive hydrogen ion beam leaving a duoplasmatron source aperture. This implies that there is an optimum source aperture radius for each application. In particular, when high currents are required, this aperture may be large—i.e., greater than 0.05 in. radius. The gas flow from the source into the vacuum system may then become excessive; an extraction system which allows the aperture radius to be increased without this attendant gas flow, is described.