PIC simulation study of electron kinetic effects on nonlinear plasma waves

Abstract

We have studied electron kinetic effects on nonlinear plasma waves using 1D PIC simulation. First, electron kinetic effects on electron holes propagating in density homogeneous region is studied. Electron holes (EHs) are known to be generated by streaming instability after magnetotail reconnection and to propagate to Earth’s polar region along the magnetic field line. While propagating, they encounter density inhomogeneity and their structures are changed due to interactions with the density gradient. Passing the density gradient region. We figured out that the oscillation is odd eigenmode trapped in the electron hole (OEM) which is closely related to the electron bouncing motion in EH potential. Potential amplitude of OEM in density inhomogeneity is asymmetric and ions are accelerated backward direction due to this potential difference. As a result, backward propagating ion acoustic waves or ion acoustic solitary waves are formed. We have derived the frequency and shape of OEM using Lewis’s formalism and they show very good agreement with the simulation results. Second, nonlinear evolution of oblique whistler waves is studied. When wave parameters correspond to non-stochastic region (or O’Neil-like damping region), vortex structures in $x-v_x$ phase space distribution, plateau distribution in parallel velocity distribution and saturation of wave energy and electron energy are commonly observed. The waves and electron energy are saturated in time scale of t∼O(100 $omega_{ce}^{-1}$). Therefore, we conclude that electron parallel energy is increased by Landau-resonance and the energy exchange is saturated after particle trapping is fully developed in those case. On the other hand, the wave parameters in stochastic region, the saturation is prevented by the stochastic change of particle motion. They lead fully thermalized phase space distribution and extreme damping of wave energy. These results imply that very large amplitude oblique whistler waves could be hardly observed in satellite data due to their very rapid damping.