Simulation of Multiturn Transverse Instabilities in Electron Storage Rings

Multiturn transverse beam instabilities place limitations on realizable beam currents in e+ e- storage rings. Such instabilities become particularly important as one considers future accelerators employing superconducting RF cavities. Higher order cavity modes (HOM) can couple to betatron and synchrobetatron harmonics and, unless sufficiently damped, will lead to instability. A code has been developed for computer simulation of the beam-HOM interaction. Results obtained agree well with experience. Of particular interest is the result that a realistic spread in synchrotron frequencies provides adequate Landau damping of quadrupole oscillations while not significantly affecting dipole behavior. The simulation predicts a quadrupole instability threshold above 1 Ampere for the Cornell elliptical superconducting cavity design placed in CESR.