空间等离子体中二维电子相空间空洞  

Two-dimensional electron phase-space holes in space plasmas

作　　者：陆全明[1] 黄灿[1] 

机构地区：[1]中国科学技术大学地球和空间科学学院,安徽合肥230026

出　　处：《中国科学技术大学学报》2007年第8期879-884,共6页JUSTC

基　　金：国家自然科学基金(40674093;40336052);教育部博士学科点专项科研基金(96035815)资助

摘　　要：利用二维粒子模拟方法分别研究了弱磁化(Ωe=0.5pωe,其中Ωe和ωpe分别为电子的回旋频率和等离子体频率)和强磁化(Ωe=2.0pωe)等离子体中电子双流不稳定性激发静电波的非线性演化过程.结果表明,在这两种情况下,基本的物理过程都是一个几乎单色的静电波在波动的线性阶段被激发,随后在非线性阶段这个静电波的波形互相合并,直至最后形成一个或几个静电孤立结构,这些结构对应于电子速度相空间中的空洞.所不同的是,在弱磁化等离子体中,形成的孤立波有着二维结构,即在两个方向都是有界的.而在强磁化等离子体中,所形成的孤立波是准一维的,即在平行于背景磁场方向是有界的,而在垂直于背景磁场方向是无界的,但是在此方向上无论是平行还是垂直电场都是有变化的.如沿着平行于背景磁场的方向切割静电孤立结构,这两种情况下的孤立波的平行电场都具有双极结构,而垂直电场有单极结构,这些结果和在地球极区上空的观测相符.另外,在强磁化等离子体中,电子空洞可激发静电哨声波,并破坏这些静电孤立结构,直至静电哨声波足够强后这些静电孤立结构消失.Two-dimensional （2D） electrostatic particle-in-cell simulations were performed to investigate the nonlinear evolution of electron bi-stream instability in weakly （Ω2e = 0. 5ωpe, where Ωe and cope are the electron cyclotron frequency and electron plasma frequency, respectively） and strongly （Ωe =2ωpe） magnetized plasma. The results show that nearly monochromatic electrostatic waves are firstly excited, then these waves coalesce with adjacent waves. At last one or several solitary waves are formed, which corresponds to electron phase-space holes. In weakly magnetized plasma, these holes have two-dimensional structures, which are isolated in both directions parallel and perpendicular to the background magnetic field. In strongly magnetized plasma, these electron holes have quasi-one-dimensional structures. The parallel extent is limited while the perpendicular extent is unlimited. However, the amplitude of the electric fields is varied along the perpendicular direction. In both cases, in these holes, the parallel cut of the parallel electric field （Ex） exhibits bipolar structures while the perpendicular electric field Ey is unipolar. The results are consistent with observations in auroral region. We also find that electrostatic whistler waves are unstable in strongly magnetized plasma, which can destroy the electrostatic solitary structures.

关 键 词：电子空洞 静电孤立结构 粒子模拟 静电哨声波 

分 类 号：P354[天文地球—空间物理学] O534[天文地球—地球物理学]