Investigation of fast beam-ion instability (FBII) in wake function formalism for the Indus-2 storage ring

Abstract

The fast beam ion instability (FBII) in electron storage ring is widely studied by solving two coupled equations of motion for electrons and ions. The instability growth rate was estimated from the analytical method and also from the numerical method using strong–weak and strong–strong interactions among the electrons and ions. In a storage ring, several ion species exists, and each of them have different ion frequencies at different locations along the circumference, due to strong focusing lattice. This creates a spread in ion frequencies, and that helps in damping the instability effect via Landau damping. In essence, ions couple the electron beam with different oscillating frequencies. The combined contributions of multi-gas species and optics variation in the lattice are taken care by solving the fast ion instability in the wake function formalism. Here, the wake field produced by the ions is estimated following a similar procedure, which is being used for the cavity like structure inside the vacuum chamber. Since the associated wake function due to ions last for duration more than the bunch to bunch separation duration, it drives multi-bunch instability. We investigate the possibility of FBII for the Indus-2 storage ring using the growth rate formulation of conventional multi-bunch instability, and the results are presented. Also a suitable bunch filling pattern is mooted for suppression of the FBII.