The Efficiency of Ion Stochastic Heating by a Monochromatic Obliquely Propagating Low-Frequency Alfven Wave

Abstract

The process of ion heating by a monochromatic obliquely propagating low-frequency Alfven wave is investigated. This process can be roughly divided into three stages: at first, the ions are picked up by the Alfven wave in several gyro-periods and a bulk velocity in the transverse direction is achieved; then, the ions are scattered in the transverse direction by the wave, which produces phase differences between the ions and leads to ion heating, especially in the perpendicular direction; and finally, the ions are stochastically heated due to the sub-cyclotron resonance. In this paper, with a test particle method, the efficiency and time scale of the ion stochastic heating by a monochromatic obliquely propagating low-frequency Alfven wave are studied. The results show that with the increase of the amplitude, frequency, and propagation angle of the Alfven wave, the efficiency of the ion stochastic heating increases, while the time scale of the ion stochastic heating decreases. With the increase of the plasma beta β, the ions are stochastically heated with less efficiency, and the time scale increases. We also investigate the heating of heavy ion species (He2+ and O5+), which can be heated with a higher efficiency by the oblique Alfven wave.