Nonlinear Interaction of Low-frequency Alfven Waves and Ions

The interaction between Alfven waves and particles is a critical phenomenon in space and laboratory plasmas, and it has been observed that low-frequency Alfven waves can accelerate and heat ions through subharmonic resonant interactions. In this study, we use test particle simulations to verify the nonlinear heating of parallelly propagating low-frequency Alfven waves on ions and analyze the underlying process in terms of the Poincare section. Our results demonstrate that low-frequency Alfven waves can periodically pick up ions, leading to oscillations of average parallel velocity and temperature of the plasma by phase mixing, ultimately resulting in the stabilization of acceleration. Furthermore, we have developed an analysis that can estimate the time required for heating and accelerating. In the case of multiple waves, our findings indicate that the presence of more chaotic modes does not necessarily result in better wave heating. We have also discussed the effect of random phases on the heating process. Overall, this research sheds light on the crucial role played by the interaction between Alfven waves and particles in astrophysics and provides new insights into the mechanisms underlying the heating and acceleration of ions through subharmonic resonant interactions with low-frequency Alfven waves. These findings may have significant implications for the understanding of plasma dynamics in a range of astrophysical environments.