Previous electrostatic particle-in-cell （PIC） simulations have pointed out that elec- tron phase-space holes （electron holes） can be formed during the nonlinear evolution of the electron two-stream instability. The parallel cuts of the parallel and perpendicular electric field have bipolar and unipolar structures in these electron holes, respectively. In this study, two-dimensional （2D） electromagnetic PIC simulations are performed in the x - y plane to investigate the evolution of the electron two-stream instability, with the emphasis on the magnetic structures associated with these electron holes in different plasma conditions. In the simulations, the background magnetic field （Bo = Boer） is along the x direction. In weakly magnetized plasma （Ωe 〈ωpe, where Ωe and ωpe are the electron gyrofrequency and electron plasma frequency, respectively）, several 2D electron holes are formed. In these 2D electron holes, the parallel cut of the fluctuating magnetic field δBx and δBz has unipolar structures, while the fluctuating magnetic field δBy has bipolar structures. In strongly magnetized plasma （Ωe 〉 ωpe）, several quasi-lD electron holes are formed. The electrostatic whistler waves with streaked structures of Ey are excited. The fluctuating mag- netic field δBx and δBz also have streaked structures. The fluctuating magnetic field δBx and δBy are produced by the current in the z direction due to the electric field drift of the trapped elec- trons, while the fluctuating magnetic field δBz can be explained by the Lorentz transformation of a moving quasielectrostatic structure. The influences of the initial temperature anisotropy on the magnetic structures of the electron holes are also analyzed. The electromagnetic whistler waves are found to be excited in weakly magnetized plasma. However, they do not have any significant effects on the electrostatic structures of the electron holes.
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 AlDen 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.
