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

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.