Speaker
Description
In hadron synchrotrons coherent bunch modes and their loss of Landau damping thresholds are important to determine active feedback requirements and bunch intensity limits. At low or medium energies space charge is the dominant collective force acting on the longitudinal bunch distribution. Usually simple g-factor or impedance models are applied, assuming a transversely constant force and a cutoff harmonic in the frequency domain. We show that improved space charge models are required to account for the transverse variation of the longitudinal force, which result in an additional frequency spread. We focus on parameters typical at injection energies in ion synchrotrons, with bunches that are long relative to the beam pipe diameter. Mode spectra and finite thresholds for the loss LD are identified from grid-less, spectral tracking simulations with the improved space charge models. The similarities to coherent modes in trapped non-neutral plasma clouds is pointed out.