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First experimental report of nonlinear collimator in the SuperKEKB

Shinji Terui*, Yoshihiro Funakoshi†, Naoko Iida, Takuya Ishibashi, Haruyo Koiso, Akio Morita, Shu Nakamura, Yukiyoshi Ohnishi, Hiroshi Sugimoto et al.

Giacomo Broggi

Katsunobu Oide

Andrii Natochii

Qingyuan Liu

Kyo Shibata, Kenta Uno, and Mulee Yao

  • *Contact author: sterui@mail.kek.jp
  • †Contact author: yoshihiro.funakoshi@kek.jp
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Phys. Rev. Accel. Beams 29, 041002 – Published 8 April, 2026

DOI: https://doi.org/10.1103/ys83-2xqh

Abstract

SuperKEKB collimator system protects the superconducting final focusing magnets (QC1 and QC2) from quenching caused by beam halo particles. For effective shielding, the minimum aperture of vertical collimators is set smaller than the physical aperture of QC1. However, such collimators become dominant sources of beam coupling impedance, which can limit the maximum beam current due to impedance-driven instabilities. To address this issue, a nonlinear collimator (NLC) was introduced in February 2024. NLC is designed to reduce both beam backgrounds and collimator impedance, thereby suppressing beam instabilities caused by short-range wakefields. In this paper, we describe the results on impedance effects, beam background reduction, and beam lifetime when the nonlinear collimation system is turned on and off. These results validate the NLC concept and offer a promising approach for future high-luminosity colliders.

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Phys. Rev. Accel. Beams 29, 041002– Published 8 April, 2026
  • Received 15 November 2025
  • Accepted 18 March 2026
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