Speaker
Description
The half integer resonance is a potential cause of significant emittance growth, beam loss, and thus a possible performance limitation on high intensity hadron rings. Of key importance is the transverse redistribution of the beam with space charge, as it approaches resonance (in most cases from above). The behaviour is a combination of both coherent and incoherent effects whose relative importance has a sensitive dependence on a few key parameters: a better understanding of these would be a valuable tool in minimising loss.
Using simulations and measurements of resonance crossing on the ISIS synchrotron in storage ring mode, with coasting beams and various optimised tune ramps, we investigate evolution of profiles and compare them with predictions from simple theoretical models. In particular, resonance models with frozen space charge for representative distributions, provide useful predictions of location and locus of stable and unstable fixed points as the beam distributions evolve. The hope is that these models will give useful insight and better understanding of observed redistributions of beam with space charge, allowing for improved control. The relation of these and other relevant measurements to losses in operational RCS mode will also be reviewed.