任意磁场位形下弱相对论等离子体的普遍色散关系

由相对论回旋动力论方程出发,推导出弱相对论非均匀等离子体的普遍色散关系。该色散关系可以适用于任意的磁场位形和任意有限频率。在色散关系中把带有速度平方项分母的奇异积分用等离子体漂移色散函数解析地表示出来,从而可以把这一结果用于较系统地解析或半解析地研究由弱相对论效应,磁场的梯度和曲率,回旋频移等共振驱动的各种微观不稳定性的性质。由于推导时考虑了温度各向异性的麦氏分布函数,因而可以直接推广并应用到损失锥非平衡分布的情况。文中还演示了它在低杂漂移不稳定性研究中的应用。由该色散关系出发,可以简捷并系统地得到Drake等人的结果。 关键词：     

托卡马克中漂移不稳定性的回旋动理学二维本征模方程

从弗拉索夫方程出发，导出了托卡马克等离子体中漂移不稳定性的回旋动理学二维本征模积分方程组。该方程组保留了离子的动理学效应，包括沿磁场的运动、磁场梯度和曲率漂移以及有限拉莫半径效应。与传统的采用气球模表象得到的一维回旋动理学方程(其只能给出不稳定模沿磁场线的结构)不同，该方程组不仅能给出托卡马克等离子体中漂移不稳定模的径向结构，同时还考虑了由离子的环形性漂移引起的相邻极向模之间的线性耦合，进而得到模的极向结构。该结果为相应的数值模拟研究提供了理论基础。     

磁场和温度对相对论电磁双流不稳定性的影响

本文在考虑到约束磁场B_0和等离子体温度T的情况下,导出了相对论电磁双流不稳定性的普遍色散关系。并对几种简化情况进行了分析,结果发现磁场和温度对于K⊥B_0这种电磁不稳定性具有较强的抑制作用,而且电磁不稳定性与温度的关系因波的种类不同而异。相对论效应可加强K⊥B_0的电磁不稳定性的发展,抑制静电不稳定性。最后对回旋波色散关系进行了数值计算,得到了不稳定性判据和引起不稳定性的最佳值。     

无碰撞电流片低频电磁模不稳定性：MHD模型

利用含无电阻广义Ohm定律的可压缩磁流体力学(MHD)理论，研究了在具有剪切磁场的无碰撞电流片中低频电磁模不稳定性，假定等离子体压力各向同性，推导出了三维扰动传播波模的色散关系.色散关系的数值求解集中在电流片中间平面(z=0)和半厚度边缘(z=1)上，并分别考虑了二维传播和三维传播，以及不同的离子惯性长度情况.主要结果如下：1)对 于二维扰动传播(k_z=0)的波，在z=0平面上，Alfven波增长率最大，不稳定的波 频率 和波数范围也更宽.离中间平面越远，增长率越小，波数区域越小.同时，随着离子惯性长度 的增大，Alfven波不稳定性的增长率变大.2)对于三维扰动传播(k_z≠0)的波， 哨声是 不稳定的.在电流片中间平面上，哨声有明显的增长率；而在离子惯性区外边，哨声的增长 率还变大.3)在电流片中间(z=0)平面上，低频波主要是电流不稳定性激发的.在离中间 平面较远处，电流、密度和压力的梯度不稳定性变得更重要. 关键词： 无碰撞电流片 磁流体力学 色散关系 不稳定性     

托卡马克中漂移不稳定性的回旋动理学二维本征模方程

从弗拉索夫方程出发,导出了托卡马克等离子体中漂移不稳定性的回旋动理学二维本征模积分方程组。该方程组保留了离子的动理学效应,包括沿磁场的运动、磁场梯度和曲率漂移以及有限拉莫半径效应。与传统的采用气球模表象得到的一维回旋动理学方程(其只能给出不稳定模沿磁场线的结构)不同,该方程组不仅能给出托卡马克等离子体中漂移不稳定模的径向结构,同时还考虑了由离子的环形性漂移引起的相邻极向模之间的线性耦合,进而得到模的极向结构。该结果为相应的数值模拟研究提供了理论基础。     

托卡马克等离子体中动力剪切阿尔芬波不稳定性的数值研究

用积分本征模方程研究了在托卡马克等离子体中包含全部动力学效应的动力剪切阿尔芬波模 (无论是否存在温度梯度). 引入了一个新的积分变量，将实平面的积分解析延拓到复平面. 这样可以同时研究增长模和阻尼模. 结果表明，在有离子温度梯度(ITG)的情况下，激发动 力剪切阿尔芬不稳定性所需的等离子体压强梯度比激发理想磁流体动力学气球模不稳定性的 阈值低得多，没有ITG时两者相同. 与动力无碰撞气球模结果不同，当有限ITG存在时，剪切 阿尔芬模存在第二稳定区. 关键词： 动力剪切阿尔芬模 磁流体气球模 阈值压强梯度     

环形等离子体中电子温度梯度不稳定性的粒子模拟

用粒子模拟方法求解描述环形等离子体中电子温度梯度静电模的回旋动力学方程.方程采用圆磁通面的轴对称环形几何系统，考虑了有限拉摩半径、电子渡越频率k_∥v _∥以及环形漂移(曲率和磁场梯度)运动w_D(v²_⊥,v ²_∥,θ)的效应.简述了粒子模拟的基本方法.采用了四阶变步长积分格式，使计算省时、简便.讨论了模的基本特征 , 并且给出了临界梯度对电子温度与离子温度之 关键词： 电子温度梯度不稳定性 粒子模拟 变步长积分格式 临界梯度     

等离子体高频不稳定性的高阻抗探针测量

采用高阻抗探针，测量了热电子等离子体的高频扰动，扰动频率与外磁场的关系及爆发区域匠实验观察表明，高频扰动为离子漂移回旋不稳定性。     

高能量粒子尾隆分布情况下的色散函数研究

当同时使用离子(或电子)回旋及中性束注入方式加热等离子体时,高能量粒子的能量分布函数一般应为尾部隆起(简称尾隆)分布。这种具有正能量梯度区域的分布函数更容易激发不稳定性,同时由于分布函数尾部隆起,在色散关系中引入了新的色散函数。主要研究了这种新色散函数的计算方法,结果表明：色散函数实部是关于原点对称的奇函数;而虚部则是关于纵轴对称的偶函数。色散函数的实部有2~4 个极值点且极值点的位置与尾隆分布函数的能量梯度Δ 有关、虚部有1~3 个极值点但极值点位置与Δ 无关。当其宗量趋于无穷大时,色散函数的值趋于零。当尾隆分布趋近于麦克斯韦分布时,用该方法计算的结果与色散函数表中给出的结果非常吻合。     

热压强对磁化等离子体中静电双流不稳定性的影响

一、引 言 在等离子体中,当电子与离子之间发生相对运动并且其相对运动速度VD超过某个阈值时,体系就会成为不稳定的.例如,当Te=Ti而VD>Vthe时就会出现毕尼曼(Buneman)不稳定性;而当Te》Ti和VD〉Vi.时出现的是离子声(ion-acoustic)不稳定性.其中Te和Ti 分别为电子和离子的温度;Vthe=和 分别为电子热速度和离子声速;m和M分别为电子和离子质量.本文在考虑到电子和离子热压强的情况下,给出了磁化等离子体中静电双流不稳定性的普遍色散关系,把以前文献[1-3]中常用的三种不同形式的色散关系作为特例而包括进来.最后对四种形式的色散关系进…     

Generation of broadband electrostatic waves in Earth's magnetotail

The theory that broad-band electrostatic waves (BEN) in Earth's magnetotail are trapped-electron ("BGK") modes is reexamined. Electron/ion beams analyzed for a realistic magnetized-plasma source model with kappa distributions are found to drive an unstable spectrum of broad angular range over several orders of magnitude in f, up to (0.1-0.2)f(pe). Analysis indicates that trapping essential for the BGK paradigm is good only at the highest f, whereas most of the spectrum has minimal trapping and can be driven by electron/ion beam instabilities. A new model is proposed in which trapped-electron modes exist only at the highest f band, whereas electron/ion beam instabilities drive the bulk of the broad-band spectrum below that. BEN wave data from ISEE-1 and ISEE-3 show large angles of propagation with respect to the magnetic field for ff(ce) is observed only in a narrow angular range around the magnetic field and may be BGK modes. This predicts that the BEN solitary waves in the source region are not in BEN well into the lobe.     

Instabilities responsible for magnetic turbulence in laboratory rotating plasma

Instabilities responsible for magnetic turbulence in laboratory rotating plasma are investigated. It is shown that the plasma compressibility gives a new driving mechanism in addition to the known Velikhov effect due to the negative rotation frequency gradient. This new mechanism is related to the perpendicular plasma pressure gradient, while the density gradient gives an additional drive depending also on the pressure gradient. It is shown that these new effects can manifest themselves even in the absence of the equilibrium magnetic field, which corresponds to nonmagnetic instabilities.     

Role of flow shear in the ballooning stability of tokamak transport barriers

A tokamak's confinement time is greatly increased by a transport barrier (TB), a region having a high pressure gradient and usually also a strongly sheared plasma flow. The pressure gradient in a TB can be limited by ideal magnetohydrodynamic instabilities with a high toroidal mode number n ("ballooning modes"). Previous studies in the limit n--> infinity showed that arbitrarily small (but nonzero) flow shears have a large stabilizing influence. In contrast, the more realistic finite n ballooning modes studied here are found to be insensitive to sub-Alfvénic flow shears, provided the magnetic shear s approximately 1 (typical for TBs near the plasma's edge). However, for the lower magnetic shears that are associated with internal transport barriers, significantly lower flow shears will influence ballooning mode stability, and flow shear should be retained in the analysis of their stability.     

Parametric instabilities in magnetized bi-ion and dusty plasmas

The excitation of low frequency modes of oscillations in a magnetized bi-ion or dusty plasma with parametric pumping of the magnetic field is analysed. The equation of motion governing the perturbed plasma is derived and parametrically excited transverse modes propagating along the magnetic field are found. With multiple ion species or charged dust present, a number of different circularly polarized modes can be excited. The stability of these modes is investigated as a function of the plasma parameters. The modulational instabilities of large amplitude normal modes, modified by the extra ion species or dust and propagating along the magnetic field, are also investigated Article presented at the International Conference on the Frontiers of Plasma Physics and Technology, 9–14 December 2002, Bangalore, India.     

Turbulent particle transport in magnetized plasmas

Particle transport in magnetized plasmas is investigated with a fluid model of drift wave turbulence. An analytical calculation shows that magnetic field curvature and thermodiffusion drive an anomalous pinch. The curvature driven pinch velocity is consistent with the prediction of turbulence equipartition theory. The thermodiffusion flux is found to be directed inward for a small ratio of electron to ion pressure gradient, and it reverses its sign when increasing this ratio. Numerical simulations confirm that a turbulent particle pinch exists. It is mainly driven by curvature for equal ion and electron heat sources. The sign and relative weights of the curvature and thermodiffusion pinches are consistent with the analytical calculation.     

Velocity gradient driven flute instabilities in plasmas

The effect of velocity gradient across the magnetic field on the low frequency flute modes is examined in detail, using the normal mode analysis. It is shown that some new type of instabilities driven primarily by the velocitygradient arise and these excited modes eventually attain the convective saturation. The onset of plasma turbulence due to these instabilities may possibly be one of the major contributors for anomalous heating process and enhanced plasma resistivity.     

Magnetic reconnection in collisionless plasmas

A class of processes involving magnetic field reconnection, in collisionless plasmas and magnetic configurations where the field undergoes a finite change of direction, is investigated. Reconnecting modes that rely on the effects of electron Landau resonance and density gradient for their excitation are found to require the analytical or numerical treatment of four consecutive asymptotic regions. The influence of finite electron temperature gradient in the region where the effects of electron Landau resonance prevail, and the convection of energy toward the region where ion Landau resonance is dominant tend to dampen these modes. Conversely, significant distortions of the ion distribution can follow their excitation. The relevance of the obtained results to experimental observations on laboratory plasmas and in space physics is discussed. Different processes are involved with magnetic reconnection in magnetic configurations where the field does not have appreciable shear but has a neutral surface on which it vanishes.     

The Pulsational Instability of Non-Isothermal Magnetized Accretion Disk with Self-Gravity in the Transition Zone

By analyzing the fifth-order dispersion relation, the influence of coupled magnetic field and self-gravity on the pulsational instability of gas pressure dominated accretion disk is investigated. Our main results are that the viscous modes become more stable with the increase of self-gravity, magnetized field and viscosity, while they enhance the instabilities of acoustic modes. The effect of self-gravity to the instability is much greater than that of magnetic field in transition zone of the accretion disk. Especially, the self-gravity affects the thermal-modes and acoustic modes strongly. Finally, we discuss our results.     

THE KINETIC EFFECTS OF THE RUNAWAY ELECTRONS DURING THE DISCHARGE PROCESS IN THE TOROIDAL SYSTEM

In this paper, the kinetic effects of the runaway electrons during the discharge process in the toroidal system are investigated, taking into account the effects of the, curvature and the gradient of the magnetic field. The density and the temperature of the electrons are inhomogeneous and some criterions of the.instabilities are obtained.