Longitudinal solitons in bunched beams

Stable, coherent, longitudinal oscillations have been observed in several accelerators. Within the context of perturbation theory, the beam parameters and machine impedance often suggest these oscillations should be Landau damped. When nonlinear effects are included, long-lived, stable oscillations become possible for low intensity beams. In this paper we report observations of stable humps in bunched beams and present a theoretical framework for their description. Implications for bunched beam stochastic cooling are considered.