参量激励过程中三波耦合的一般色散关系(Ⅰ)最容易激励参量不稳定性的频率和波矢条件

讨论了在各向同性的均匀无耗电离层背景下激励参量不稳定性的三波耦合过程．首先从波的非线性耦合理论出发，分析入射电磁波和多个等离子体本征波模间的耦合情况；然后得到了无耗情况下参量激励过程满足的色散关系，在激励等离子体波的临界情况下表现为两种频率和波矢匹配条件，进而从理论上证明最容易激励参量不稳定性的条件是耦合生成电子Langmuir波和离子声波．     

等离子体片边界层中静电不稳定性产生的波-粒动量交换率

本文介绍了非均匀等离子体片外边缘离子束流-密度梯度漂移不稳定性的二级理论。二级动量交换率的计算表明, 模型等离子体中冷、暖束流离子的场向动量以及暖束流离子的横向动量可以被静电波来减小。这些波是由离子束流-密度梯度漂移不稳定性产生的。这些结果对于理解等离子体片外边缘等离子体的各向同性化和热化是很有用的。      

离子非线性极化漂移对动力学Alfvén孤波特性的影响

考虑离子极化漂移中非线性项对动力学Alfven孤波特性的影响，采用双流体模型研究磁化等离子体中低频动力学Alfven稀疏型孤波的特性，所得的结果表明，两种类型的动力学Alfven稀疏型孤波在磁层中大范围内均存在（参数β约为10^-6,0,1,β为等离子体的热压之磁压之比，即β＝20μ0nT/B0^2)，它们或以超Alfven速或以亚Alfven速传播。同时发现在β值较小（10^-6-10^-4)时，离子极化漂移非线性项对动力学Alfven孤波特性有较大的影响，不可忽略，而在较大值时（β－0．1），此修正作用不大，由于动力学Alfven孤波允许平行电场存在，故它对等离子体中带电粒子的加速和能化起重要作用。同时也对离子的横向加速有一定的作用，它使一种新的能量转换机制成为可能。     

参量激励过程中三波耦合的一般色散关系(Ⅱ)一般色散关系以及泵场阈值和增长率

本文讨论了各向同性的均匀有耗电离层背景下激励参量不稳定性的三波耦合过程．首先推导有耗情况下参量激励过程中的一般色散关系,然后针对文献得出的两种频率和波矢匹配条件计算激励参量不稳定性所需要的泵波阈值场强和受激励的等离子体波的增长率．结果表明,过密加热时泵场阈值与电子碰撞频率和离子碰撞频率的乘积成正比,不同于以前的一些理论模型得到的泵场阈值与碰撞频率的一次方成正比的结论;欠密加热比过密加热需要能量更高的高频泵波来激励参量不稳定性．     

无碰撞激波上游低频波的激发及其对激波耗散机制的影响

由于很大一部分来自激波上游的粒子被激波面所反射,因此在准平行无碰撞激波的上游存在着等离子体束流．通过一维混合模拟方法,计算了束流密度较小(nb／n0=0．02)和较大(nb／n0=0．2)两种不同情形下的等离子体束流不稳定性．结果表明,在束流密度较小时,束流激发的主要是平行于背景磁场方向传播的右旋波,此波动只能对束流粒子产生影响,包括减速和加热．在束流密度较大时,束流可同时激发平行和反平行于背景磁场方向传播的右旋波,除能对束流粒子产生影响外,还可通过非共振作用加速和加热背景粒子．文中对准平行无碰撞激波耗散机制的影响也进行了讨论。     

等离子体片边界层处离子的随机加速

本文讨论宽频带静电噪声对等离子体片边界层处粒子的随机加速问题.计算表明:宽频带静电噪声会使离子轨道在相空间Poincare截面上一定范围内无规行走, 该范围与扰动电场的振幅、频率和波矢有关;引起的离子随机加速使一部离子能获得较高的能量, 在等离子体片参数下预计最大能量可达1000keV量级;对电子, 随机效应不明显.该结果为等离子体片中高能离子的存在这一长时观测特性提供一种新的可能产生机制.      

太阳风中低频离子静电孤波

本文给出在太阳风超声速流动条件下,离子静电孤波的传播特性,结果与Helios1,2卫星观测的静电离子噪声做了比较。离子声波扰动的非线性发展使太阳风等离子体呈规则的小尺度起伏,离子声波在马赫锥外传播,因此理论预言密度起伏不沿着太阳风速度方向,而是在横向方向.      

离子温度对磁化等离子体中非线性静电波的影响

本文讨论了无碰撞磁化低β等离子体中离子温度对非线性静电波的影响。结果表明,在参量α≡T_i/T_e≠0条件下,存在着三种非线性静电波(T_i和T_e分别为离子和电子的热能):在波速ν_p>(1+α)(1/2)c_s情况下存在着非线性离子回旋周期波;在(1+α)(1/2)c_scosθp<(1+α)(1/2)c_s情况下存在着离子声孤立波;在v_p<(1+α)(1/2)c_scosθ情况下存在着非线性离子声周期波。当参量α增加时,孤立波的波幅(最大电位)减小,而另外两种非线性周期波的电位幅度都几乎保持不变。      

磁化等离子体中斜传播的离子孤波

近几年卫星空间电场测量经常证认出局地非线性离子静电波,它们可能与极光粒子加速有直接关系。这些静电波被认为或者是离子声波模的演化,或者是静电离子逥旋波模的演化结果。本文研究了磁场中斜传播小振幅离子非线性波的演化,得到非线性Schrodinger方程。结果表明离子声孤波和离子迴旋孤波都是可能的。计算结果与卫星S(3-3)电场测量比较,可以很好说明部分测量结果。      

碘工质射频离子推力器栅极系统束流特性仿真

为分析碘工质射频离子推力器束流特性,应用粒子云网格算法（PIC）,对碘工质射频离子推力器栅极系统进行三维数值仿真。碘工质电离产物中除了大量存在的I⁺,还包含少量I₂⁺、I²⁺、I³⁺几种多价离子。对添加多价离子前后束流特性的仿真结果进行对比,得出该栅极系统离子空间分布、电势分布、离子相空间分布以及束流、束流发散角,并对变密度工况下束流大小进行统计。计算结果表明,程序能较好地模拟离子在栅极系统中的运动情况：添加多价离子后,等离子体悬浮电势有所上升,鞍点电势有所下降,但整体电势分布的变化幅度较小;添加多价离子后束流大小略有增加,束流发散角略有减小,通过理论分析可知仿真所得理论推力及理论比冲均有小幅度增加;放电室等离子体数密度增加到约2.4×10¹⁷m^-3时,该栅极系统达到了束流引出的极限,后续增大等离子体密度引出束流不增反降。模拟结果可以为碘工质射频离子推力器栅极系统的设计提供参考。     

Solitary and periodic waves in magneto–rotating plasmas: Effect of the Kappa–Cairns distributed electrons

The nonlinear propagation of ion–acoustic (IA) waves in a magneto–rotating plasma is studied by considering the Kappa-Cairns electron distribution. Employing the perturbation scheme, Korteweg–de Vries equation is derived. It is seen that both positive and negative potential solitons can be supported in the present plasma model. The numerical results reveal that the Kappa-Cairns distributed electrons modify features of the electrostatic waves significantly. The effects of non–thermal parameters, plasma rotation frequency, ion temperature, and the wave propagation angle on electrostatic solitary wave structures are also discussed here. It is found that the plasma parameters considerably influence the propagation of IA waves in rotating plasmas. Furthermore, using the bifurcation theory of planar dynamical systems to the K-dV equation, we have presented the existence of solitary and periodic traveling waves. Our study may be helpful to understand the behavior of ion–acoustic wave in the rotating plasma.     

Ion- and electron-acoustic solitons and double layers in multi-component space plasmas

A general model for the ion- and electron-acoustic solitons and double layers in a multi-component unmagnetized plasma consisting of background electrons, counter-streaming electron beams and ions is discussed. The model is based on the multi-fluid equations and the Poisson equation, and uses the Sagdeev pseudo-potential techniques. For identical counter-streaming electron beams and depending upon the plasma parameters, three types of solutions, namely, ion-acoustic, slow and fast electron-acoustic soliton/double layer, are possible. Generally, the ion acoustic solitons have positive potentials, slow-electron acoustic solitons have negative potentials and fast electron-acoustic solitons and double layers can have either positive or negative potentials depending on the core electron density. As beam speed is increased, first ion-acoustic and then slow electron-acoustic solitons disappear. At large beam speed, only fast electron-acoustic solitons/double layers survive. The results may be relevant to the observations of the electrostatic solitary waves (ESWs) observed in the Earth’s magnetosphere.     

太阳风质子束流的演化

太阳神飞船观测表明，太阳风高速流中质子束分量相对于核分量的密度随日心距离增加而增加．提出解释这一观测现象的机理并给出二维数值模拟结果．由于阿尔芬波速随日心距离增加而减少，第二支左旋波将与更多的质子共振，把部分原来属于核分布的质子拉到束分布中来．用数值模拟方程方法求解回旋波共振导致的准线性扩散方程，数值结果与观测结果相符合．     

Broadband electrostatic noise and low-frequency waves in the Earth’s magnetosphere

Broadband electrostatic noise (BEN) is commonly observed in different regions of the Earth’s magnetosphere, eg., auroral region, plasma sheet boundary layer, etc. The frequency of these BENs lies in the range from lower hybrid to the local electron plasma frequency and sometimes even higher. Spacecraft observations suggest that the high and low-frequency parts of BEN appear to be two different wave modes. There is a well established theory for the high-frequency part which can be explained by electrostatic solitary waves, however, low-frequency part is yet to be fully understood. The linear theory of low-frequency waves is developed in a four-component magnetized plasma consisting of three types of electrons, namely cold background electron, warm electrons, warm electron beam and ions. The electrostatic dispersion relation is solved, both analytically and numerically. For the parameters relevant to the auroral region, our analysis predict excitation of electron acoustic waves in the frequency range of 17 Hz to 2.6 kHz with transverse wavelengths in range of (1–70) km. The results from this model may be applied to explain some features of the low-frequency part of the broadband electrostatic noise observed in other regions of the magnetosphere.     

Two dimensional simulation of amplitude modulated electron plasma waves

Highly modulated waves near electron plasma frequency with both parallel and perpendicular polarization have been observed near diffusion region at dayside and in the tail region. In this paper, two dimensional Particle-In-Cell (PIC) simulation was performed to study the possible generation mechanism of these modulated electron plasma waves. It is shown that weak beam instability could generate the modulated Langmuir wave and the ambient magnetic field plays an important role in the formation of modulation. When the weak beam has loss cone distribution, highly modulated upper hybrid waves are generated and propagate with large angle to the ambient magnetic field. The properties of these modulated waves are discussed and compared with observations.     

Small amplitude ion acoustic solitons in a weakly magnetized plasma with anisotropic ion pressure and kappa distributed electrons

The Zakharov–Kuznetzov (ZK) equation is derived for nonlinear electrostatic waves in a weakly magnetized plasma in the presence of anisotropic ion pressure and superthermal electrons. The anisotropic ion pressure is defined using Chew–Goldberger–Low (CGL) while a generalized Lorentzian (kappa) distribution is assumed for the non-thermal electrons. The standard reductive perturbation method (RPM) is employed to derive the two dimensional ZK equation for the dynamics of obliquely propagating low frequency ion acoustic wave. The influence of spectral index (kappa) of non-thermal electron on the soliton is discussed in the presence of anisotropic ion pressure in plasmas. It is found that ion pressure anisotropy and superthermality of electrons affect both the width and amplitude of the solitary waves. On the other hand the magnetic field is found to alter the dispersive property of the plasma only, and hence the width of the solitons is affected while the amplitude of the solitary waves is independent of external magnetic field. The numerical results are also presented for illustrations.     

二维静电孤立波的粒子模拟研究

利用二维粒子模拟程序研究了双流不稳定性激发静电波并演化为静电孤立波的物理过程.计算结果表明,在线性增长阶段,主要激发的是沿磁场传播的静电波;在非线性演化阶段,相邻的静电波会互相合并,直至形成静电孤立波,并可激发静电哨声波.还研究了磁场强度和离子温度对此过程的影响.当磁场强度比较小时,无法形成静电孤立波,只有磁场强度达到一定程度后静电孤立波才能形成;同时,离子温度会影响静电孤立波的稳定性,当离子温度比较小时,静电孤立波的稳定性减弱,在演化一段时间后会逐渐瓦解.      

Electron acoustic solitary waves in the Earth’s magnetotail region

Satellite observations have revealed solitary potential structures in the Earth’s magnetotail region. These structures have both positive (compressive) and negative (rarefactive) electrostatic potentials. In this paper we study the electron-acoustic solitary waves (EASWs) in an unmagnetized plasma consisting of cold plasma electrons and isothermal ions with two different temperatures. Using the reductive perturbation method, the nonlinear evolution of such structures is studied. The numerical computations are performed to study the role of two temperature ions in the generation of EASWs. In this case, the model supports the existence of both positive and negative electrostatic potentials with bipolar pulses. The electric field associated with these positive and negative solitary structures are numerically computed. The present study could be useful to construe the compressive and rarefactive electric field bipolar pulses associated with the BEN type emissions in the magnetospheric regions where the electron beams are not present.     

色散和耗散对Alfven孤立波的影响

利用变数变换和解析积分的方法,分别找到了带色散项的DNLS方程和带耗散的MKdV方程的一类解析解,给出了存在孤立波的条件。