Suppression of the Fast Beam-Ion Instability by Tune Spread in the Electron Beam due to Beam-Beam Effects

TL;DR

This paper models the fast beam-ion instability in electron beams, demonstrating that beam-beam effects can induce sufficient tune spread to suppress the instability in electron-ion colliders.

Contribution

It introduces a new model incorporating beam-beam induced tune spread to explain suppression of FII, relevant for collider design.

Findings

Beam-beam effects can suppress FII at high beam-beam parameters.

The model estimates suppression conditions for eRHIC parameters.

Tune spread from nonlinear potential helps stabilize the beam.

Abstract

The fast beam-ion instability (FII) is caused by the interaction of an electron bunch train with the residual gas ions. The ion oscillations in the potential well of the electron beam have an inherent frequency spread due to the nonlinear profile of the potential. However, this frequency spread and associated with it Landau damping typically is not strong enough to suppress the instability. In this work, we develop a model of FII which takes into account the frequency spread in the electron beam due to the beam-beam interaction in an electron-ion collider. We show that with a large enough beam-beam parameter the fast ion instability can be suppressed. We estimate the strength of this effect for the parameters of the eRHIC electron-ion collider.