Speaker
Description
The beam quality of high-intensity proton and ion bunches in the CERN Proton Synchrotron (PS) is limited by longitudinal microwave instability at transition crossing. This single-bunch instability manifests as a rapid longitudinal emittance blow-up and impacts, for instance, the intensity and bunch length to the AWAKE experiment. In this contribution, results of complete parameter scans are presented to experimentally establish the beam stability limits. These are compared to detailed tracking simulations with the BLonD code, including collective effects with the longitudinal impedance model, beam feedback loops, and the gamma transition jump. Remarkable agreement with measurements is obtained for instability thresholds and micro-bunch structures. Nonetheless, the characteristics of the simulated instability strongly depend on the modelling of longitudinal space charge, which focuses the micro-bunches but also introduces significant numerical noise. The results improve the understanding of performance limitations due to transition crossing and guide future mitigation strategies.
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