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@inproceedings{karpov:ipac2021-wepab227,
author = {I. Karpov and M. Gadioux},
title = {{Mechanism of Longitudinal Single-Bunch Instability in the CERN SPS}},
booktitle = {Proc. IPAC'21},
pages = {3161--3164},
eid = {WEPAB227},
language = {english},
keywords = {impedance, simulation, synchrotron, coupling, emittance},
venue = {Campinas, SP, Brazil},
series = {International Particle Accelerator Conference},
number = {12},
publisher = {JACoW Publishing, Geneva, Switzerland},
month = {08},
year = {2021},
issn = {2673-5490},
isbn = {978-3-95450-214-1},
doi = {10.18429/JACoW-IPAC2021-WEPAB227},
url = {https://jacow.org/ipac2021/papers/wepab227.pdf},
note = {https://doi.org/10.18429/JACoW-IPAC2021-WEPAB227},
abstract = {{Understanding the origin of beam instabilities is essential for reaching the highest performance of proton synchrotrons. In the present work, the Oide-Yokoya eigenvalue method of solving the linearised Vlasov equation was used to shed light on the mechanism of longitudinal single-bunch instability in the CERN SPS. In particular, semi-analytical calculations were done for the full longitudinal impedance model, taking into account the RF nonlinearity. The obtained results agree well with macro-particle simulations and are consistent with available beam measurements. For the first time, the instability has been interpreted as a coupling of radial modes within a single azimuthal mode, due to a strong potential-well distortion of the synchrotron-frequency distribution. To avoid this instability, a higher RF voltage is required at a given emittance. Thus, the instability mechanism is very different from the loss of Landau damping, which, in contrast, is mitigated by a lower RF voltage. This understanding also allowed us to optimise the RF voltage programmes during the acceleration cycle for high-intensity bunches used in the AWAKE experiment at CERN.}},
}