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Beam-breakup instability in anharmonic ion-focused-regime channels.

The beam-breakup instability is analyzed for a high-current electron beam transported in an anharmonic ion channel. A multicomponent model of transverse beam motion is used to treat the damping effect of nonlinear focusing. An analytic dispersion relation is obtained, and'growth rates are calculated for specific beam and channel profiles. The instability is completely suppressed when a stability criterion obtained from the dispersion relation is satisfied. The analytic results are in good agreement with the results of a particle-simulation code. Nonlinear development of the instability is discussed briefly