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Design of a storage ring based on a fixed-field alternating-gradient configuration with an internal target for heavy-ion beams with stochastic charge state conversions

Yoshihiro Ishi*, Tomonori Uesugi, and Yoshiharu Mori

Katsuhisa Nishio

  • Institute for Integrated Radiation and Nuclear Science, Kyoto University, Kumatori, Osaka 590-0494, Japan

  • *Contact author: ishi.yoshihiro.4m@kyoto-u.ac.jp
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Phys. Rev. Accel. Beams 29, 050101 – Published 6 May, 2026

DOI: https://doi.org/10.1103/th5l-mq3q

Abstract

In heavy-ion accelerators used for radioactive isotope production, the accelerated beam is typically directed onto a target and then discarded in a beam dump. To make more efficient use of the beam, recycling of the beam passed through the target is proposed in the framework of the so-called energy recovery internal target (ERIT). In the ERIT system, the target is irradiated by a circulating beam, while the energy lost in the target is recovered using rf cavities. So far, such a system has been realized only for proton beams. Here, an ERIT system for heavy-ion beams is demonstrated for the first time. A major challenge is the circulation of ions with multiple atomic charge states. After passing through the target, ions rapidly reach an equilibrated charge-state distribution, independent of the initial charge state. This stochastic charge-state conversion (SCSC) leads to rapid beam-emittance growth. To mitigate this effect, we develop a method to match the closed orbits and betatron functions of different charge states at the target location, based on a scaling fixed-field alternating-gradient (FFA) lattice. We present the design of such an FFA ring and show, through 6D beam-tracking simulations, that the transverse emittance growth induced by SCSC can be significantly reduced over a practical number of turns, whereas longitudinal emittance growth remains significant and is discussed separately.

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Phys. Rev. Accel. Beams 29, 050101– Published 6 May, 2026
  • Received 14 July 2025
  • Accepted 9 April 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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