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State-of-the-art beam loss minimization at high-intensity beam operation of the 3 GeV rapid cycling synchrotron at the Japan Proton Accelerator Research Complex

P. K. Saha*, H. Harada, F. Tamura, K. Okabe, M. Yoshimoto, Y. Shobuda, H. Okita, K. Kojima, T. Nakanoya et al.

H. Hotchi

S. Hatakeyama, T. Takayanagi, and K. Yamamoto

  • Accelerator Division, J-PARC Center, Japan Atomic Energy Agency (JAEA), 2-4 Shirakata, Tokai-mura, Naka-gun, Ibaraki 319-1195, Japan

  • *Contact author: saha.pranab@j-parc.jp.
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Phys. Rev. Accel. Beams 28, 074201 – Published 25 July, 2025

DOI: https://doi.org/10.1103/tbyh-jcq3

Abstract

At the 3-GeV rapid cycling synchrotron (RCS) of the Japan Proton Accelerator Research Complex, we have minimized the beam loss at high-intensity beam operation up to the designed beam power of 1 MW. This was accomplished through systematic numerical simulations and experimental studies conducted over 2 years from 2020 and 2022. We first focused on mitigating uncontrolled beam losses originating from the foil scattering of the circulating beam, which results in high residual radiation levels, particularly in the injection area. These uncontrolled beam losses were well mitigated by reducing the stripper foil size and optimizing the injection beam size. Subsequently, we attempted to minimize the space charge effects and the associated beam losses at 1 MW by implementing several measures, such as refining both longitudinal and transverse injection paintings, correcting betatron resonances, and optimizing betatron tunes at injection. Consequently, we reduced beam losses throughout the RCS, including the collimator area, by 80% as compared to those observed at 1-MW trial operation in 2020. The residual beam loss at 1 MW is now estimated to be well below 10−3, which is primarily attributed to residual foil scattering-induced beam losses. Notably, beam losses in areas other than the collimator section are uncontrolled and required to be well minimized to ensure stable operation and regular accelerator maintenance. We have considerably reduced the machine activation, achieving a 1-order-of-magnitude decrease at the collimator compared to that in 2020. This improvement has enabled the RCS to maintain more than 98% availability for user operation recently. The simulation and measurement results, demonstrating good agreement, provide a detailed understanding of the beam loss mechanism at each step and guide the implementation of effective optimizations.

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Phys. Rev. Accel. Beams 28, 074201– Published 25 July, 2025
  • Received 4 October 2024
  • Accepted 20 June 2025
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