Title: Observation of bunch motion due to the longitudinal dipole-coupled bunch instability at CESR
Abstract: In the past a longitudinal dipole-coupled bunch instability had limited high current operation at CESR and resulted in a degradation of luminosity performance. A longitudinal feedback system successfully damps this instability and the exchange of superconducting RF cavities for normal conducting RF cavities in CESR has further reduced the instability's strength. In this paper measurements of the longitudinal dynamics using a dual-axis synchroscan streak camera are presented. The measurements were made on single trains of bunches and give a characterization of the instabilities and modes of oscillation.