初始大扰动条件下双流系统的粒子相空间振荡  

Particle phase space oscillations of the two-stream instability under strong initial perturbation

作　　者：焦鹿怀 付松[1] 倪彬彬[1] 张援农[1] JIAO LuHuai;FU Song;NI BinBin;ZHANG YuanNong(Department of Space Physics,School of Electronic Information,Wuhan University,Wuhan 430072,China)

机构地区：[1]武汉大学电子信息学院空间物理系,武汉430072

出　　处：《地球物理学报》2024年第1期1-11,共11页Chinese Journal of Geophysics

基　　金：国家自然科学基金(42025404,42188101,41974186,42174188)资助。

摘　　要：双流系统产生的不稳定性过程是近地空间中常见的等离子体不稳定性现象.地球磁尾、等离子体片边界层、地球弓激波、太阳风、极隙区和极光加速区观测到的静电孤立波被认为是由双流不稳定性产生.地球空间环境并非均匀稳态,因此对双流系统演化过程的研究往往需要考虑初始的扰动.利用所建立的动理论粒子云模型方法,我们研究了初始大扰动下双流系统的不稳定性现象,发现初始大扰动条件下粒子相空间产生振荡现象,且振荡频率与初始扰动的空间波数有关,电场与电场能量也存在该频率成分.通过线性理论,求解出了粒子相空间振荡频率.它与粒子云模拟得到的频率一致.该频率为朗缪尔振荡频率的基础之上叠加一个与初始扰动的空间波数有关的频率偏移量.我们改变等离子体频率,进一步验证了上述结论.该研究结果表明初始扰动能够对双流系统的不稳定性现象产生重要影响,对于加深理解地球磁层中双流系统的演化过程有重要参考意义.The instability generated by two-stream system is a common plasma instability in geospace.Electrostatic solitary waves that are observed in the Earth′s magnetotail,plasma sheet boundary layer,the Earth′s bow shock,the solar wind,the cusp,and in the auroral acceleration region,are generated by the two-stream instability.The geo-space environment is neither uniform nor stationary,so the initial perturbation should be considered in the study of two-stream system evolution.Based on our developed kinetic particle-in-cell model,we investigate the instability of the two-stream system with strong initial perturbation.We find that particles oscillate in the phase space.The oscillation frequency is related with the spatial wavenumber of initial perturbation.The frequency component of electric field and electric energy also exists.By linear theory,we obtain the oscillation frequency.It is consistent with the oscillation frequency obtained by particle-in-cell simulation.This frequency consists of two components:one is the Langmuir frequency of the system,the other is a frequency offset related to the spatial wavenumber of the initial perturbation.We change the plasma frequency,and confirm the conclusion.Our results indicate that the initial perturbation condition is very important to the instability of the two-stream system,and advance our understanding on the process and consequence of the evolution of the two-stream system in the Earth′s magnetosphere.

关 键 词：双流不稳定性 粒子云模拟 初始扰动 线性理论 

分 类 号：P351[天文地球—空间物理学]