• Open Access

Longitudinal mode-coupling instabilities of proton bunches in the CERN Super Proton Synchrotron

Ivan Karpov
Phys. Rev. Accel. Beams 26, 014401 – Published 12 January 2023

Abstract

In this paper, we study single-bunch instabilities observed in the CERN Super Proton Synchrotron (SPS). According to the linearized Vlasov theory, radial or azimuthal mode-coupling instabilities result from a coupling of bunch-oscillation modes, which belong to either the same or adjacent azimuthal modes, respectively. We show that both instability mechanisms exist in the SPS by applying the Oide-Yokoya approach to compute van Kampen modes for the realistic longitudinal impedance model of the SPS. The results agree with macroparticle simulations and are consistent with beam measurements. In particular, we see that the uncontrolled longitudinal emittance blowup of single bunches observed before the recent impedance reduction campaign (2018–2021) is due to the radial mode-coupling instability. Unexpectedly, this instability is as strong as the azimuthal mode-coupling instability, which is possible in the SPS for other combinations of bunch length and intensity. We also demonstrate the significant role of rf nonlinearity and potential-well distortion in determining these instability thresholds. Finally, we discuss the effect of the recent impedance reduction campaign on beam stability in single- and double-rf configurations.

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  • Received 30 September 2022
  • Accepted 19 December 2022

DOI:https://doi.org/10.1103/PhysRevAccelBeams.26.014401

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.

Published by the American Physical Society

Physics Subject Headings (PhySH)

Accelerators & Beams

Authors & Affiliations

Ivan Karpov*

  • CERN, CH-1211 Geneva, Switzerland

  • *ivan.karpov@cern.ch

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Issue

Vol. 26, Iss. 1 — January 2023

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