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Investigation of sudden beam loss at SuperKEKB

Shinji Terui*, Takuya Ishibashi, Hitomi Ikeda, Testuo Abe, Mitsuru Shirai, Yusuke Suetsugu, Takaaki Yamaguchi, Yoshihiro Funakoshi, Kenta Uno et al.

Mulee Yao, Kyo Shibata, Naoki Akita, Xiuguang Jin, and Masaki Ishida

  • *Contact author: sterui@mail.kek.jp
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Phys. Rev. Accel. Beams 29, 093501 – Published 15 September, 2026

DOI: https://doi.org/10.1103/pyl3-rfjg

Abstract

In SuperKEKB, mitigation of sudden beam losses (SBLs) is essential to improve the luminosity. SBL refers to the rapid loss of a substantial portion of the stored beam current within a few revolutions. During SuperKEKB operation from 2019 to 2024, over 200 SBL events were observed, in which a beam abort with 5%–40% beam loss occurred within 2–3 turns, making high beam current operation difficult. The frequency of SBLs was very high, especially in the low-energy ring (LER). The occurrence of SBLs was highly concentrated during beam-current upgrade phases, presenting a severe operational bottleneck. While SBLs were rare during stable operations at lower currents, the frequency escalated to more than five events per day when operating at higher beam currents. These frequent events triggered intense beam losses, resulting in 11 quenches of the final-focus superconducting quadrupole magnets (QCS) within a period of less than three weeks in December 2024. Furthermore, SBL events could damage the collimator heads and the Belle II detector, causing devastating impacts on operation. SBLs occurred under both noncollisional and collisional conditions, but only under circumstances involving a small beam size at the interaction point and a high beam current. Most SBL events were accompanied by vacuum pressure bursts, primarily in the wiggler section of the LER, and an increase in beam size was also observed during these events. To investigate this phenomenon, SBL was artificially reproduced during beam operation and subsequently discharging the clearing electrodes. Inspecting the wiggler beam pipe, we found black stains, and removal of these stains led to a significant reduction in the frequency of SBLs. The black stains we discovered were identified as degraded vacuum sealant through observations using synchrotron radiation. This paper reports the results of an artificial reproduction test of the SBL phenomenon (knocking on the beam pipe, discharge inside the beam pipe), and an investigation of these black stains, including their composition and formation mechanism.

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Phys. Rev. Accel. Beams 29, 093501– Published 15 September, 2026
  • Received 27 February 2026
  • Accepted 28 August 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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