Longitudinal beam dynamics with active cavity systems
Abstract
In storage-ring-based light sources, harmonic cavities are commonly employed to lengthen the bunch, thereby mitigating collective effects and enhancing beam lifetime. However, this dual-RF configuration also introduces significant challenges, as the impedance of the fundamental modes can drive the beam into a longitudinal coupled-bunch instability regime. To mitigate this effect, low-level radio-frequency (LLRF) feedback is proposed to reduce the effective impedance experienced by the beam. This work investigates longitudinal beam dynamics in the PETRA-IV dual-RF system with normal-conducting cavities, explicitly accounting for the LLRF feedback loop. Both analytical modeling and numerical simulations are employed to characterize the onset and growth of coupled-bunch instabilities. The results show that, with appropriately defined LLRF specifications, the destabilizing influence of the cavity fundamental modes can be effectively suppressed, enabling stable operation of the storage ring at the design current. This work highlights the critical role of RF feedback systems in ensuring robust longitudinal stability, thereby supporting the realization of PETRA-IV's design goals and contributing to the broader development of next-generation synchrotron light sources, where high brilliance and operational reliability are essential.
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BibTeX
@misc{li2026longitudinal,
title = {{Longitudinal beam dynamics with active cavity systems}},
author = {Chao Li and Yong-Chul Chae and Sven Pfeiffer and Chris Christou},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2605.27613},
eprint = {2605.27613},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2605.27613},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Longitudinal beam dynamics with active cavity systems
AU - Chao Li
AU - Yong-Chul Chae
AU - Sven Pfeiffer
AU - Chris Christou
PY - 2026
DA - 2026/09/15
PB - arXiv
DO - 10.48550/arxiv.2605.27613
UR - https://arxiv.org/abs/2605.27613
AB - In storage-ring-based light sources, harmonic cavities are commonly employed to lengthen the bunch, thereby mitigating collective effects and enhancing beam lifetime. However, this dual-RF configuration also introduces significant challenges, as the impedance of the fundamental modes can drive the beam into a longitudinal coupled-bunch instability regime. To mitigate this effect, low-level radio-frequency (LLRF) feedback is proposed to reduce the effective impedance experienced by the beam. This work investigates longitudinal beam dynamics in the PETRA-IV dual-RF system with normal-conducting cavities, explicitly accounting for the LLRF feedback loop. Both analytical modeling and numerical simulations are employed to characterize the onset and growth of coupled-bunch instabilities. The results show that, with appropriately defined LLRF specifications, the destabilizing influence of the cavity fundamental modes can be effectively suppressed, enabling stable operation of the storage ring at the design current. This work highlights the critical role of RF feedback systems in ensuring robust longitudinal stability, thereby supporting the realization of PETRA-IV's design goals and contributing to the broader development of next-generation synchrotron light sources, where high brilliance and operational reliability are essential.
ER -