Section III. Ion sources and instrumentation
Optimizing the geometry of a negative ion sputter source

https://doi.org/10.1016/0168-583X(84)90510-XGet rights and content

Abstract

In order to avoid isotope fractionating effects due to slight fluctuations in the position, direction or divergence of the emerging beam, the emittance of an AMS ion source has to be lower than the acceptance of the following beam handling system. The emittance of a negative ion sputter source is determined by the energy spread of the sputtered ions and by its extraction geometry. For various configurations of the latter, we have calculated particle trajectories. Greatly reduced aberrations are attained if the electric field close to the emitting surface is nearly uniform and only weakly focussing and if the acceleration takes place in at least two lens sections. The single acceleration gap of our Hortig-type ion source [1] has therefore been replaced by a two-stage accelerating lens. Further, the curvature of the field at the surface of the sputter target is controlled by an additional electrode.

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Stanford University, Stanford, CA 94305, USA.

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