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Nondestructive beam envelope measurements using beam position monitors for low-beta heavy ion beams in a superconducting linear accelerator

Takahiro Nishi1,*, Tamaki Watanabe1, Taihei Adachi1, Ryo Koyama2, Naruhiko Sakamoto1, Kazunari Yamada1, and Osamu Kamigaito1

  • *Contact author: takahiro.nishi@riken.jp
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Phys. Rev. Accel. Beams 28, 092803 – Published 29 September, 2025

DOI: https://doi.org/10.1103/8ct7-x1xf

Abstract

In a superconducting linear accelerators (linacs), accurately monitoring beam dynamics is essential for minimizing beam losses and ensuring stable operations. However, destructive diagnostics must be avoided in superconducting sections to prevent the occurrence of particulates and outgassing, rendering direct measurements of the beam envelope particularly challenging. This study presents a nondestructive method that uses beam position monitors (BPMs) to estimate the transverse beam envelope based on measurements of the quadrupole moment of the beam distribution. Although this concept was originally proposed in the 1980s, its application, especially to hadron beams, has been limited because of low signal sensitivity and the accuracy constraints associated with conventional BPM geometries. To overcome these challenges, we employed cos2θ-type BPMs, which offer improved sensitivity to quadrupole components and are well suited for low-β heavy ion beams. This method was applied to the heavy ion beams in the superconducting RIKEN linac (SRILAC), for which data from eight BPMs were combined with transfer matrix calculations and supplemental wire scanner data. The resulting beam envelope estimates exhibited good agreement with conventional quadrupole scan results, demonstrating the feasibility of this technique for routine, nondestructive beam monitoring in superconducting accelerator sections.

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Phys. Rev. Accel. Beams 28, 092803– Published 29 September, 2025
  • Received 21 April 2025
  • Accepted 6 August 2025
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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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