New diagnostics and cures for coupled-bunch instabilities

Abstract

As circular accelerators move towards larger numbers of bunches and higher beam currents, the task of diagnosing and curing coupled-bunch instabilities becomes ever harder. This paper describes the use of phase space tracking, i.e. reconstruction of bunch phase space trajectories, as a comprehensive instability diagnostic. A new instability cure is also presented, based on recent insights into the dynamics of unevenly-filled rings. Data is shown from PEP-II and the ALS, where "optimally shaped" uneven fills have yielded significant increases in instability thresholds.