Numerical study for the two-beam instability due to ions in electron-storage rings

Abstract

We discuss the two-beam instability which is caused by interactions between ions and the electron beam in electron storage rings. Motion of beam and ions trapped in the beam potential was studied by using a simulation method based on a rigid Gaussian beam model. We consider two types of the two beam instability depending on the trapped time. One is the so-called ion trapping instability, in which ions are accumulated every revolution. The growth of the coupled bunch mode, which was obtained by simulations, was consistent with experiments in the KEK-photon factory. The other is the fast ion instability, in which ions are trapped during only the passage of a single series of bunches (bunch train). Simulations gave the growth of the couple bunch mode for the KEK-B factory.