- Physical Review Journals
All JournalsPhysics Magazine

Physical Review Accelerators and Beams

Reuse & Permissions

It is not necessary to obtain permission to reuse this article or its components as it is available under the terms of the Creative Commons Attribution 4.0 International license. This license permits unrestricted use, distribution, and reproduction in any medium, provided attribution to the author(s) and the published article's title, journal citation, and DOI are maintained. Please note that some figures may have been included with permission from other third parties. It is your responsibility to obtain the proper permission from the rights holder directly for these figures.

Export citation

Export citation

Choose format for download:

Download Citation
  • Open Access

Three-dimensional collimator design for suppressing transverse single-bunch instabilities in crab-waist colliders

Takuya Ishibashi1,2,*, Zeyuan Meng3, and Demin Zhou1,2

  • *Contact author: takuya.ishibashi@kek.jp
PDF

Phys. Rev. Accel. Beams 29, 063001 – Published 29 June, 2026

DOI: https://doi.org/10.1103/vcpn-ds5b

Abstract

The collimator system is a significant source of impedance in ring colliders and can drive transverse mode coupling instabilities (TMCIs) through vertical dipolar wakefields. In this study, we investigate the impact of collimator geometry on wake potentials using electromagnetic simulations based on simplified and realistic models. Various taper shapes, jaw widths, and structural modifications such as hollowed and asymmetric configurations are evaluated with a focus on reducing the vertical dipolar kick factor. Three mitigation strategies are proposed and benchmarked using the pyheadtail tracking code, with the SuperKEKB Low Energy Ring used as a case study. Our results show that the implementation of hollowed exponential taper jaws, especially in one-sided layouts, leads to a substantial reduction in the total βy-weighted dipolar kick factor and increases the TMCI threshold by up to approximately 90%.

View figure in article

Physics Subject Headings (PhySH)

Article Text

References (41)

  1. P. Raimondi, 2nd SuperB Workshop, INFN-LNF, Frascati, 2006, http://www.lnf.infn.it/conference/superb06/.
  2. M. Zobov et al., Test of “Crab-waist” collisions at the DAΦNEΦ factory, Phys. Rev. Lett. 104, 174801 (2010).
  3. SuperKEKB design report, https://kds.kek.jp/event/15914/.
  4. FCC. collaboration et al., FCC-ee: The lepton collider: Future circular collider conceptual design report volume 2, Eur. Phys. J. ST 228, 261 (2019).
  5. The CEPC Study Group, CEPC conceptual design report: Volume 1-accelerator, arXiv:1809.00285.
  6. D. A. Epifanov et al., Project of Super Charm-Tau Factory, Phys. At. Nucl. 83, 944 (2020).
  7. Qing Luo, Weiwei Gao, Jieqin Lan, Wei Li, Xu Derong et al., Progress of conceptual study for the accelerators of a 2–7 GeV super tau charm facility at China, in Proceedings of the 10th International Particle Accelerator Conference (IPAC’19), Melbourne, Australia (JACoW, Geneva, Switzerland, 2019), pp. 643–645.
  8. KEKB B-Factory Design Report, KEK Report, 95-7, 1995.
  9. PEP-II: An asymmetric B factory: Conceptual design report, SLAC-418, 1993.
  10. T. Ishibashi, M. Migliorati, D. Zhou, K. Shibata, T. Abe, M. Tobiyama, Y. Suetsugu, and S. Terui, Impedance modelling and single-bunch collective instability simulations for the SuperKEKB main rings, J. Instrum. 19, P02013 (2024).
  11. D. Gibellieri, A. Ghribi, M. Migliorati, C. Zannini, and M. Zobov, Impact of the geometric impedance of collimators on beam stability in FCC-ee, in Proceedings of the International Particle Accelerator Conference, IPAC’25, Taipei, Taiwan (2025), paper WEPM074.
  12. Yuan Zhang, Na Wang, Kazuhito Ohmi, Demin Zhou, Takuya Ishibashi, and Chuntao Lin, Combined phenomenon of transverse impedance and beam-beam interaction with large Piwinski angle, Phys. Rev. Accel. Beams 26, 064401 (2023).
  13. Demin Zhou, Kazuhito Ohmi, Yoshihiro Funakoshi, Yukiyoshi Ohnishi, and Yuan Zhang, Simulations and experimental results of beam-beam effects in SuperKEKB, Phys. Rev. Accel. Beams 26, 071001 (2023).
  14. Kazuhito Ohmi and Yuan Zhang, Effects of space charge force on the beam-beam mode coupling instability, Phys. Rev. Accel. Beams 27, 101001 (2024).
  15. Kaoru Yokoya, Impedance of slowly tapered structures, Report No. CERN SL/90-88 (AP), 1990.
  16. G. Stupakov, Low frequency impedance of tapered transitions with arbitrary cross sections, Phys. Rev. ST Accel. Beams 10, 094401 (2007).
  17. I. Zagorodnov and K. L. F. Bane, Wakefield calculations for 3D collimators, in Proceedings of the 10th European Particle Accelerator Conference, Edinburgh, Scotland, 2006 (EPS-AG, Edinburgh, Scotland, 2006), pp. 2859–2861.
  18. B. Podobedov and S. Krinsky, Transverse impedance of tapered transitions with elliptical cross section, Phys. Rev. ST Accel. Beams 10, 074402 (2007).
  19. Igor Zagorodnov, Karl L. F. Bane, and Gennady Stupakov, Calculation of wakefields in 2D rectangular structures, Phys. Rev. ST Accel. Beams 18, 104401 (2015).
  20. A. Burov and V. Danilov, Suppression of transverse bunch instabilities by asymmetries in the chamber geometry, Phys. Rev. Lett. 82, 2286 (1999).
  21. G. Bassi Alexei Blednykh, V. Smaluk, and R. Lindberg, Impedance modeling and its application to the analysis of the collective effects, Phys. Rev. Accel. Beams 24, 104801 (2021).
  22. The GdfidL Electromagnetic Field Simulator, http://www.lnf.infn.it/conference/superb06/.
  23. ECHO4D, https://echo4d.de/.
  24. A. Oeftiger, An overview of PyHEADTAIL, Report No. CERN-ACC-NOTE-2019-0013, http://cds-lb.cern.ch/record/2672381/files/CERN-ACC-NOTE-2019-0013.pdf.
  25. Yukiyoshi Ohnishi, Tetsuo Abe, Toshikazu Adachi, Kazunori Akai, Yasushi Arimoto, Kiyokazu Ebihara, Kazumi Egawa, John Flanagan, Hitoshi Fukuma, Funakoshi Yoshihiro et al., Accelerator design at SuperKEKB, Prog. Theor. Exp. Phys. 2013, 03A011 (2013).
  26. T. Ishibashi, S. Terui, Y. Suetsugu, K. Watanabe, and M. Shirai, Movable collimator system for SuperKEKB, Phys. Rev. Accel. Beams 23, 053501 (2020).
  27. Gennady V. Stupakov, Impedance of small angle collimators in high frequency limit, Report No. SLAC-PUB-8857, 2001.
  28. Victor Smaluk, Richard Fielder, Alexei Blednykh, Guenther Rehm, and Riccardo Bartolini, Coupling impedance of an in-vacuum undulator: Measurement, simulation, and analytical estimation, Phys. Rev. ST Accel. Beams 17, 074402 (2014).
  29. A. Khan and V. Smaluk, Convergence study of wakefield simulations with GdfidL and ECHO3D, Nucl. Instrum. Methods Phys. Res., Sect. A 1082, 171073 (2025).
  30. CST Studio Suite, https://www.3ds.com/products-services/simulia/products/cst-studio-suite/.
  31. Y. Suetsugu, T. Kageyama, K. Shibata, and T. Sanami, Latest movable mask system for KEKB, Nucl. Instrum. Methods Phys. Res., Sect. A 513, 465 (2003).
  32. S. DeBarger, S. Metcalfe, C. Ng, T. G. Porter, J. Seeman, M. Sullivan, U. Wienands et al., The PEP-II movable collimators, Report No. SLAC-PUB-11752, 2001.
  33. Gennady Stupakov and Demin Zhou, Transverse wakefields due to asymmetric protrusions into a vacuum chamber, Nucl. Instrum. Methods Phys. Res., Sect. A 764, 378 (2014).
  34. T. Ishibashi, Impedance budget and single-bunch collective effects in the SuperKEKB low energy ring with a new collimation system after the first long-term shutdown, in Proceedings of the eeFACT2025, Tsukuba, Japan (to be publshed).
  35. A. Morita, NLC (What NLC is.), The 26th KEKB Accelerator Review Committee, Dec. 13-14 (2022), https://www-kekb.kek.jp/MAC/2022/.
  36. Shinji Terui, Yoshihiro Funakoshi, Takuya Ishibashi, Haruyo Koiso, Mika Masuzawa, Yu Morikawa, Akio Morita, Shu Nakamura, Hiroyuki Nakayama, Ohnishi Yukiyoshi et al., Collimator challenges at SuperKEKB and their countermeasures using nonlinear collimator, Phys. Rev. Accel. Beams 27, 081001 (2024).
  37. S. Terui et al., Report on the results of the first experiments on a nonlinear collimator for, in Proceedings of PASJ2024, Yamagata, Japan (2024), pp. 104–109, https://www.pasj.jp/web_publish/pasj2024/proceedings/PDF/THOA/THOA04.pdf.
  38. N. Ohuchi, Y. Arimoto, K. Akai, K. Aoki, N. Higashi, K. Kanazawa, M. Kawai, T. Kawamoto, H. Koiso, Y. Kondou et al., SuperKEKB beam final focus superconducting magnet system, Nucl. Instrum. Methods Phys. Res., Sect. A 1021, 165930 (2022).
  39. J. W. Flanagan M. Tobiyama and A. Drago, Bunch by bunch feedback systems for SuperKEKB rings, in Proceedings of PASJ2016, Chiba, Japan (2016), pp. 144–148, https://www.pasj.jp/web_publish/pasj2016/proceedings/PDF/TUOM/TUOM06.pdf.
  40. E. Métral and M. Migliorati, Longitudinal and transverse mode coupling instability: Vlasov solvers and tracking codes, Phys. Rev. Accel. Beams 23, 071001 (2020).
  41. S. Terui, T. Ishibashi, M. Shirai, Y. Suetsugu, K. Shibata, K. Kanazawa, H. Hisamatsu, Y. Ohnishi, Y. Funakoshi, and M. Tobiyama, Report on collimator damaged event in SuperKEKB, in Proceedings of the 12th International Particle Accelerator Conference (IPAC’21), Campinas, Brazil (JACoW, Geneva, Switzerland, 2021), pp. 3541–3544, 10.18429/JACoW-IPAC2021-WEPAB359.

Outline

Information

Phys. Rev. Accel. Beams 29, 063001– Published 29 June, 2026
  • Received 10 February 2026
  • Accepted 4 May 2026
Crossmark - Check for updates button
Creative Commons Logo

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

Sign In to Your Journals Account

Filter

Filter

Article Lookup

Enter a citation