Instabilities of high-order beam modes driven by space-charge coupling resonances

Space charge presents a fundamental limitation to high intensity circular accelerators. Its effects are especially important in the latest designs for high-intensity proton rings, which require beam losses much smaller than presently achieved in existing facilities. It is therefore necessary to understand the major space-charge effects which could lead to emittance growth and associated beam loss. In this paper, we explore the excitation of high-order collective beam modes and associated instabilities driven by space-charge coupling resonances. Such studies help us to understand energy exchange and emittance growth driven by space-charge coupling. They also have direct application to the choice of a good working point in a high-intensity machine. The studies are performed using an earlier version of the Spallation Neutron Source lattice, which was used as a generic example of a circular machine. In this way, we explore the nature of the observed space-charge coupling effect and its applicability to high-intensity rings in general.