Fast beam-ion instability. II. Effect of ion decoherence

Abstract

The ionization of residual gas by an electron beam in an accelerator generates ions that can resonantly couple to the beam through a wave propagating in the beam-ion system. A beam-ion instability is studied for a multibunch train, taking into account the decoherence of ion oscillations due to the ion frequency spread. It is shown that while the decoherence does not completely suppress the instability, it makes the growth rate smaller. A comparison of analytical and numerical results indicates a good agreement with direct macroparticle simulation of the instability.