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Observation and simulation study on bunch fill pattern dependence of absorbed power in cavity HOM dampers

Takaaki Yamaguchi*, Takafumi Okada, Michiru Nishiwaki, and Tetsuya Kobayashi

  • *Contact author: yamaguc@post.kek.jp
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Phys. Rev. Accel. Beams 29, 103803 – Published 21 October, 2026

DOI: https://doi.org/10.1103/84l3-xsvr

Abstract

In the SuperKEKB accelerator, higher-order-mode (HOM) power absorbed by the HOM dampers of the superconducting (SC) cavities limits the attainment of the design electron beam current of the High Energy Ring. As regards cylindrical ferrite dampers installed in the SC cavities, we observed that their effective loss factors considerably depended on the bunch fill pattern. To investigate this behavior in detail, wakefield simulations were conducted. HOM power is generally evaluated from the numerically calculated coupling impedance, which provides only the total beam power loss within the structure. However, when multiple absorbers are present, the absorbed power of each absorber remains unknown. To address this limitation, we introduce calculation methods that utilize the local electromagnetic fields to evaluate the absorbed power. In this study, the theoretical basis of the methods is presented and applied to the SuperKEKB SC cavity.

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Phys. Rev. Accel. Beams 29, 103803– Published 21 October, 2026
  • Received 30 March 2026
  • Accepted 11 September 2026
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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.

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