Formation of electrostatic solitary waves in space plasmas: Particle simulations with open boundary conditions
Formation of electrostatic solitary waves in space plasmas: Particle simulations with open boundary conditions
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DOI：
10.1029/2001ja000286
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发表时间：
2002-12
影响因子：
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通讯作者：
T. Umeda;Y. Omura;H. Matsumoto;H. Usui
中科院分区：
文献类型：
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作者：
T. Umeda;Y. Omura;H. Matsumoto;H. Usui
[1]本文利用一维和二维开放边界静电粒子模拟方法研究了近年来航天器观测到的静电孤立波的形成过程。以前的模拟已经表明，ESW对应于由电子束不稳定性形成的Bernstein-Greene-Kruskal电子空穴。然而，由于以前的模拟是在均匀周期系统中进行的，电子束不稳定性的波粒相互作用在系统中均匀地发生。在本研究中，我们注入一个弱的电子束从一个开放的边界到背景等离子体研究的空间和时间发展的凸点尾部不稳定性的本地化源。在开放系统中，电子空穴的空间结构根据与电子束源的距离而变化。在模拟运行的早期阶段，在垂直于磁场的方向上最初均匀的电子空穴通过倾斜电子束模式的调制而变得扭曲。当电子空穴沿着磁场传播时，它们通过聚结在垂直方向上排列。在远离源的区域中的电子空穴的空间结构变为一维。在不稳定性的长期演化中，离子动力学在确定电子空穴的空间结构方面变得重要。通过与电子空穴以相同的平行相速度耦合，在靠近电子束源的区域局部激发出低混杂模。低混杂模式调制在后期激发的电子空穴，从而形成调制的一维势。由于电子空穴的垂直电场以电子空穴的漂移速度由电子空穴携带，因此即使在远离源的地方也可以观察到它们。
[1] We study formation process of electrostatic solitary waves (ESW) observed by recent spacecraft via one- and two-dimensional electrostatic particle simulations with open boundaries. The previous simulations have demonstrated that ESW correspond to Bernstein-Greene-Kruskal electron holes formed by electron beam instabilities. However, since the previous simulations were performed in uniform periodic systems, wave-particle interaction of an electron beam instability was taking place uniformly in the systems. In the present study, we inject a weak electron beam from an open boundary into the background plasma to study spatial and temporal development of a bump-on-tail instability from a localized source. In the open system, spatial structures of electron holes vary depending on the distance from the source of the electron beam. In an early phase of the simulation run, electron holes that are initially uniform in the direction perpendicular to the magnetic field become twisted through modulation by oblique electron beam modes. As the electron holes propagate along the magnetic field, they are aligned in the perpendicular direction through coalescence. Spatial structures of electron holes in a distant region from the source become one-dimensional. In a long-time evolution of the instability, ion dynamics becomes important in determining spatial structures of electron holes. A lower hybrid mode is excited locally in the region close to the source of the electron beam through coupling with electron holes at the same parallel phase velocity. The lower hybrid mode modulates electron holes excited in later phases, resulting in formation of modulated one-dimensional potentials. Since the perpendicular electric fields of electron holes are carried by the electron holes at the drift velocity of the electron holes, they can be observed even at a distant place from the source.