The Vertical Instability in a Positron Bunched Beam

Abstract

The results of experiments on the vertical instability observed in both positron and electron multibunch accumulations at the Photon Factory storage ring are presented. The betatron sidebands, which indicate a vertical instability, appear at different frequency regions depending on the polarities of the beam. The cause of these instabilities cannot be attributed to the well-known transverse wakefields induced by beam-wall interactions. We propose that these vertical instabilities are induced by electrons in a positron bunched beam, and by trapped ions in an electron bunched beam.