Production of Dense Beams of Low Energy Ions

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Abstract
Dense beams of positive ions of less than 1.0 keV energy have been produced using a duoplasmatron with an extraction voltage of 20 kV as a source. Outward radial electrostatic forces due to space charge impose a restriction upon the intensity of an ion beam while it is being formed in vacuum. This paper discusses the problem of designing the electrostatic lens system for decreasing the energy of the ions while simultaneously focusing them to produce a maximum density parallel beam. The system consisted of a unipotential lens, which was integral with the source (Radiation Dynamics type DY-1), and two additional immersion lenses. Most of the deceleration and beam compression was accomplished in the last lens. Its design was the major problem. Because a fairly exact analysis would have been very complicated, a simple approximate method for designing this lens was devised. The design values of current in the final low energy beam checked well with those from experiment.

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