- 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

Beam-based impedance measurement of HL-LHC low-impedance collimators

A. Kurtulus1,2, D. Amorim2, N. Biancacci2, X. Buffat2, L. Giacomel2, J. Leuthold1, N. Mounet2, S. Redaelli2, and J. Smajic1

  • 1Institute of Electromagnetic Fields (IEF), ETH Zurich, Zurich, Switzerland
  • 2CERN, Geneva, Switzerland

PDF

Phys. Rev. Accel. Beams 28, 103001 – Published 27 October, 2025

DOI: https://doi.org/10.1103/z197-398z

Abstract

The objective of the High Luminosity Large Hadron Collider (HL-LHC) upgrade is to attain an instantaneous luminosity that is 5 times greater than the design value of the LHC. This requires nearly 2 times higher beam intensity compared to the operational LHC value during Run 2 (2015–2018). Higher bunch intensity makes the beam more prone to coherent instabilities. To keep beam stability under control and preserve beam quality, it is therefore necessary to reduce the machine beam coupling impedance. The collimation system of the LHC is presently responsible for a significant portion of the total machine impedance budget. In this context, during the LHC long-shutdown 2 (LS2), the LHC machine has been upgraded with newly engineered low-impedance collimators whose absorbing jaws are made of molybdenum-graphite (MoGr) compared to the previously used carbon fiber composite (CFC). Secondary collimators are also coated with molybdenum (Mo) to further boost conductivity. In order to validate the benefits of the impedance reduction targeted at the collimators and to identify possible nonconformities, we performed a series of tune shift measurements on the newly installed primary and secondary collimators with LHC beams and quantified the agreement with predictions. As expected, the results show a significant reduction in the collimators’ impedance contribution. Additionally, the remaining discrepancy between measurements and predictions is investigated with 3D numerical simulations by using the Wakefield Solver of Computer Simulation Technology.

View figure in article

Physics Subject Headings (PhySH)

Article Text

References (26)

  1. R. W. Assmann et al., The final collimation system for the LHC, CERN, Geneva, Switzerland, Report No. CERN-LHC-Project-Report-919, 2006, https://cds.cern.ch/record/972336.
  2. L. Palumbo, V. G. Vaccaro, and M. Zobov, Wake fields and impedance, INFN-LNF, Frascati, Italy, Report No. LNF-94-041-P, 1995, 10.5170/CERN-1995-006.331.
  3. L. Giacomel et al., Assessment of the real part of the impedance of the LHC collimators with instability growth rate measurements, in Proceedings of the 15th International Particle Accelerator Conference, IPAC-2024, Nashville, TN (JACoW, Geneva, Switzerland, 2024), 10.18429/JACoW-IPAC2024-THPC57.
  4. N. Mounet, R. Tomás et al., High intensity beam dynamics assessment and challenges for HL-LHC, J. Instrum. 19, T05016 (2024).
  5. G. Apollinari et al., High-Luminosity Large Hadron Collider (HL-LHC): Technical design report V.0.1, CERN, Geneva, Switzerland, Report No. CERN-2017-007-M, 2017, 10.2172/1767028.
  6. E. Métral et al., Update of the HL-LHC operational scenarios for proton operation, Report No. CERN-ACC-NOTE-2018-0002, CERN, Geneva, Switzerland, 2018.
  7. D. Amorim, L. Vega Cid, N. Mounet, B. Salvant, G. Mazzacano et al., HL-LHC impedance and related effects, Report No. CERN-ACC-NOTE-2018-0087, CERN, Geneva, Switzerland, 2018.
  8. S. A. Antipov et al., Transverse beam stability with low-impedance collimators in the High-Luminosity Large Hadron Collider: Status and challenges, Phys. Rev. Accel. Beams 23, 034403 (2020).
  9. S. Antipov, Effect of collimator coating thickness on HL-LHC octupole thresholds, in Proceedings of the 134th HSC Section Meeting (CERN, Geneva, Switzerland, 2018), https://indico.cern.ch/event/703766/.
  10. E. Chapochnikova, Beam-based impedance measurements, CERN Yellow Rep. School Proc. 3, 107 (2017).
  11. C. Accettura et al., Resistivity characterization of molybdenum-coated graphite-based substrates for high-luminosity LHC collimators, Coatings 10, 361 (2020)..
  12. A. Kurtulus et al., Detailed electromagnetic characterisation of HL-LHC low impedance collimators, in Proceedings of the 12th International Particle Accelerator Conference, Campinas, SP, Brazil (JACoW, Geneva, Switzerland, 2021), 10.18429/JACoW-IPAC2021-THPAB235.
  13. Computer Simulation Technology, Dassault Systèmes, cst studio suite, https://www.3ds.com/products-services/simulia/products/cst-studio-suite/.
  14. G. Stupakov, Low frequency impedance of tapered transitions with arbitrary cross sections, Phys. Rev. ST Accel. Beams 10, 094401 (2007).
  15. D. Valuch, Excitation by ADT and active bunch by bunch tune measurements, in Proceedings of the 129th SPS and LHC Machine Protection Panel Meeting (CERN, Geneva, Switzerland 2016).
  16. M. Soderen and D. Valuch, ADT ObsBox data acquisition (LHC Beam Operation Committee, 2017), https://indico.cern.ch/event/645898.
  17. R. Bartolini and F. Schmidt, A computer code for frequency analysis of non-linear betatron motion, Report No. CERN SL-Note-98-017-AP, CERN, Geneva, 1998, https://cds.cern.ch/record/702438.
  18. L. Malina, Harpy: A fast, simple and accurate harmonic analysis with error propagation, in Proceedings of the 13th International Particle Accelerator Conference, IPAC-2022, Bangkok, Thailand (JACoW, Geneva, Switzerland, 2022), pp. 2326–2329, 10.18429/JACoW-IPAC2022-WEPOMS035.
  19. F. Sacherer, Transverse–part II: Bunched beams, in Proceedings of the 1st International School of Particle Accelerators “Ettore Majorana” (1977), 10.5170/CERN-1977-013.198.
  20. N. Mounet, LHC impedance and wake model, GitLab Repository, https://gitlab.cern.ch/IRIS/LHC_IW_model (2021).
  21. N. Biancacci, Interpretation of wire measurements on TCSPM, in Proceedings of the Impedance Meeting (CERN, Geneva, Switzerland, 2017), https://indico.cern.ch/event/670910/.
  22. N. Mounet, N. Biancacci, D. Amorim, and E. Vik, impedancewake2d, https://twiki.cern.ch/twiki/bin/view/ABPComputing/ImpedanceWake2D (2012).
  23. N. Biancacci et al., 2D and 3D collimator impedance modeling and experimental measurements, in CERN Yellow Reports: Conference Proceedings (CERN, Geneva, Switzerland, 2018), Vol. 1, pp. 17–23.
  24. N. Biancacci et al., Impedance simulations and measurements on the LHC collimators with embedded beam position monitors, Phys. Rev. Accel. Beams 20, 011003 (2017).
  25. O. Frasciello et al., Geometric beam coupling impedance of LHC secondary collimators, Nucl. Instrum. Methods Phys. Res., Sect. A 810, 68 (2016).
  26. A. Kurtulus, LHC collimators tune shift measurements and the modelling of collimator impedances, in Proceedings of the ABP Group Information Meeting (CERN, Geneva, Switzerland, 2023), https://indico.cern.ch/event/1244689/.

Outline

Information

Phys. Rev. Accel. Beams 28, 103001– Published 27 October, 2025
  • Received 8 April 2025
  • Accepted 17 September 2025
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