Landau damping due to octupoles of non-rigid head–tail modes

Abstract

Octupole magnets are often used as a passive mitigation for the collective instabilities in ring accelerators, also for the unstable head–tail modes in bunches. An important advantage of the octupole mitigation is the ability to suppress the intra-bunch oscillations. We investigate the non-rigid oscillations of the head–tail modes using particle tracking simulations. Stability thresholds are determined and compared with the analytic predictions. The stabilization of the modes above the thresholds, and the related emittance blowup, are demonstrated and quantified for modes of different order.