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Abstract: Here we compute the ion distribution produced by an electron beam whenion-clearing electrodes are installed. This ion density is established as anequilibrium between gas ionization and ion clearing. The transverse iondistributions are shown to strongly peak in the beam-s center, producing verynonlinear forces on the electron beam. We will analyze perturbations to thebeam properties by these nonlinear fields. To obtain reasonable simulationspeeds, we develop fast algorithms that take advantage of adiabatic invariantsand scaling properties of Maxwell-s equations and the Lorentz force.Our results are very relevant for high current Energy Recovery Linacs, whereions are produced relatively quickly, and where clearing gaps in the electronbeam cannot easily be used for ion elimination. The examples in this papertherefore use parameters of the Cornell Energy Recovery Linac project. Forsimplicity we only consider the case of a circular electron beam of changingdiameter. However, we parameterize this model to approximate non-round beamswell. We find suitable places for clearing electrodes and compute theequilibrium ion density and its effect on electron-emittance growth and halodevelopment. We find that it is not sufficient to place clearing electrodesonly at the minimum of the electron beam potential where ions are accumulated.



Autor: Georg H. Hoffstaetter, Christian Spethmann

Fuente: https://arxiv.org/







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