- Open Access
Characterization and mitigation of rf knockout during beam stacking
Phys. Rev. Accel. Beams 29, 074001 – Published 30 July, 2026
DOI: https://doi.org/10.1103/nt4f-3cfm
Abstract
Beam stacking allows a fixed field alternating gradient accelerator (FFA) to increase the extracted beam current while also enabling a flexible time structure, making FFAs a promising candidate for future spallation neutron sources and other high intensity beam applications. For successful beam stacking, beam loss caused by rf knockout must be prevented. rf knockout can occur during beam stacking because of the finite dispersion function at the rf cavity location, which is unavoidable in a scaling FFA. In this work, the rf knockout resonance is characterized and through a series of experiments at the ISIS Neutron and Muon Source, we show that it is possible to suppress losses due to rf knockout.
Physics Subject Headings (PhySH)
Article Text
References (14)
- S. Machida, S. Gallimore, B. Kirk, D. J. Kelliher, J.-B. Lagrange, C. T. Rogers, J. Pasternak, I. Gardner, R. Mathieson, T. J. Kuo, C. Hill, E. Yamakawa, D. Posthuma de Boer, and S. Sapkota, Fixed field alternating gradient accelerator (FFA) report, 2025, STFC Preprints:-62105376, http://purl.org/net/epubs/work/62105376.
- K. M. Terwilliger, L. W. Jones, and C. H. Pruett, Beam stacking experiments in an electron model FFAG accelerator, Rev. Sci. Instrum. 28, 987 (1957).
- T. Uesugi, Y. Ishi, Y. Kuriyama, Y. Mori, C. Jolly, D. J. Kelliher, J.-B. Lagrange, A. P. Letchford, S. Machida, D. W. P. de Boer, C. T. Rogers, E. Yamakawa, and M. Topp-Mugglestone, Beam stacking experiment at a fixed field alternating gradient accelerator, Phys. Rev. Accel. Beams 28, 012803 (2025).
- J. W. G. Thomason, The ISIS spallation neutron and muon source—The first thirty-three years, Nucl. Instrum. Methods A 917, 61 (2019).
- K. R. Symon, D. W. Kerst, L. W. Jones, L. J. Laslett, and K. M. Terwilliger, Fixed-field alternating-gradient particle accelerators, Phys. Rev. 103, 1837 (1956).
- T. Okawa, in Proceedings of the Annual Meeting of JPS, unpublished (1953).
- A. A. Kolomensky and A. N. Lebedev, Theory of Cyclic Accelerators (North-Holland, Amsterdam, 1966).
- K. M. Terwilliger, Radio frequency knockout of stacked beams, Report No. MURA-133, 1956.
- R. Baartman, FFAG04, Resonance crossing topics (2004), https://ffag2004.triumf.ca/programme.html.
- J. Le Duff, Integer resonance crossing in H.I. accumulator ring, eConf C7910292, 310 (1979).
- D. W. Kerst, Suppression of betatron oscillation excitation (RF knockout) by the RF accelerating system of a fixed field accelerator, MURA-215, 1957.
- L. W. Jones, C. H. Pruett, and K. M. Terwilliger, Experiments on radio frequency knockout of stacked beams, MURA-260, 1957.
- P. Barratt, I. Gardner, C. Planner, and G. Rees, RF system and beam loading compensation on the ISIS synchrotron, in Proceedings of the 2nd European Particle Accelerator Conference (1990), https://cds.cern.ch/record/963925.
- C. Jolly, D. J. Kelliher, J.-B. Lagrange, A. P. Letchford, S. Machida, D. W. Posthuma de Boer, C. T. Rogers, and A. Seville, Characterisation and mitigation of RF knockout during beam stacking—ISIS experimental data (2024), 10.5286/edata/957.
