Plasma and Fusion Research

Volume 21, 1401029 (2026)

Regular Articles

Heavy-Ion Acceleration by Nonlinear Magnetosonic Waves in a Two-Ion-Species Plasma with a Large Difference in Cyclotron Frequencies

Mieko TOIDA^1,2), Tsubasa KOTANI³⁾

1): National Institute for Fusion Science, National Institutes of Natural Sciences, Toki, Gifu 509-5292, Japan
2): The Graduate University for Advanced Studies, SOKENDAI, Toki, Gifu 509-5292, Japan
3): Data Analysis Center for Geomagnetism and Space Magnetism, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan

(Received 8 December 2025 / Accepted 2 March 2026 / Published 3 July 2026)

Abstract

In a two-ion-species plasma, a magnetosonic wave splits into two distinct modes: a low-frequency mode and a high-frequency mode. Nonlinear solitary waves corresponding to these modes can accelerate heavy ions in a plasma composed of hydrogen (H) and a heavier ion species (denoted by b). In this study, we theoretically examine the dependence of the heavy-ion acceleration on the heavy-ion mass (m_b) and the difference between cyclotron frequencies Ω_H and Ω_b. When the pulse amplitude is fixed, the heavy-ion acceleration weakens as m_b increases for both the low- and high-frequency-mode pulses. However, for the low-frequency-mode pulse, a maximum attainable amplitude exists, and this amplitude increases as the ratio Ω_H/Ω_b becomes larger. Consequently, in a plasma containing heavy ions with larger m_b, the low-frequency-mode pulse can have a larger amplitude, leading to the enhancement of the heavy-ion acceleration. These results indicate that the low-frequency-mode pulse can accelerate, for instance, oxygen (O) ions in an H-O plasma more effectively than helium (He) ions in an H-He plasma.

Keywords

magnetosonic wave, solitary wave, two-ion-species plasma, heavy-ion acceleration, Earth’s magnetosphere, comets

DOI: 10.1585/pfr.21.1401029

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