Parametric Instabilities of Waves in Magnetized Plasmas

Results from kinetic theory are reformulated in order to generalize previous equations for wave-wave interactions in magnetized plasmas.     

On the Instabilities of the Collisionless and Non-Magnetized Active Plasmas

Spontaneously excited instabilities in a uniform, collisionless and non-magnetized active plasma are studied, under the assumption that the polarisability of its active constituent is due to transitions of only one optical electron between two inversely populated energy levels. The attention is focused on non-resonant situations in which the modal frequencies of the excited waves differ significantly from the frequency of coherent electromagnetic radiation arising due to the presence of the active constituent. The longitudinal (‘acoustic’) waves in both low and high phase velocity domains, as well as the transverse (‘optical’) waves, are investigated. It is shown that the instabilities excited are most frequently aperiodical, and appear within, a comparatively large wavelength range. Their amplitude increments are evaluated. Under certain particular conditions, specified in the paper, the instabilities turn out to be periodical and to appear in very narrow wavelength bands only. Their modal frequencies and amplitude increments are also evaluated.     

Charge Shielding in Magnetized Plasmas

The shielding of a test charge imbedded into a magnetized plasma has been investigated by means of a PIC (particle‐in‐cell) model. It is shown that the ratio of the gyration radius to the Debye length is the main parameter in the analysis. For small values of this parameter the plasma surrounding the test charge is not able to compensate this additional charge and shielding does not occur. For high values of this parameter the effect of the magnetic field vanishes and the electric forces dominate. Scaling rules are given in order to compare different sets of plasma parameters.     

Three-wave Interactions in Magnetized Plasmas

This paper considers the nonlinear interaction between three waves in a warm magnetized twocomponent plasma. A general formalism is developed within a simple macroscopic theory in order to treat waves propagating in arbitrary directions. Some results of previous papers are generalized and discussed.     

Effects of External Magnetic Field on Propagation of Electromagnetic Wave in Uniform Magnetized Plasma Slabs

Absorbers and reflectors of electromagnetic waves have many applications, and so the interactions between electromagnetic waves and low-temperature plasma, particularly numerical analysis of reflection, absorption, and transmission of electromagnetic waves in unmagnetized, magnetized, nonuniform, and uniform plasma, have been a topic of intensive research. For instance, Laroussi numerically evaluated the interactions between electromagnetic waves and a uniform magnetized plasma cylinder, and Helaly and Yeh studied the scattering from nonuniform magnetized plasma cylinders.     

Diffusion in Two-dimensional Magnetized Dusty Plasmas

A molecular dynamical simulation method is used to investigate the diffusion of the two-dimensional magnetized dusty plasmas. The effects of charge and mass of the particles, as well as the external magnetic field are discussed in detail. It is shown that, relative to the mass of particulate, the charge and magnetic field have a more considerable effect on the diffusion process, particularly on the resulting structure of the system. The dependence of diffusion coefficient on the temperature is shown to be linearly changed over a wide range of temperature.     

Difusion in Two-dimensional Magnetized Dusty Plasmas

A molecular dynamical simulation method is used to investigate the difusion of the two-dimensional magnetized dusty plasmas.The efects of charge and mass of the particles,as well as the external magnetic field are discussed in detail.It is shown that,relative to the mass of particulate,the charge and magnetic field have a more considerable efect on the difusion process,particularly on the resulting structure of the system.The dependence of difusion coefcient on the temperature is shown to be linearly changed over a wide range of temperature.     

Positively Biased Probes in Magnetized Plasmas

Positively biased probes in magnetized plasmas can create several phenomena which are not described by standard probe theories. These include transient currents for pulsed electrodes in the regime of Electron MHD, relaxation oscillations induced by large probes and high frequency instabilities at the sheath‐plasma frequency. Although they may limit the use of probes for diagnostic purposes they also offer new applications and belong to the general knowledge of probes in plasmas (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Electrostatic Waves in Weakly Magnetized Quantum Plasmas

By using the quantum magnetohydrodynamic model, the electrostatic waves in weakly magnetized quantum plasmas are investigated. The electrons are treated as a quantum and magnetized species, while the ions are classical unmagnetized ones. The general dispersion relations are derived. It is shown that, both the high frequency electron waves （Langmuire wave and upper-hybrid wave） and the low frequency ion acoustic wave can propagate when the plasmas are cold.     

Compensation of Magnetic Field Instabilities in Field Cycling NMR by Reference Deconvolution

Performing a nuclear magnetic resonance (NMR) experiment in an unstable magnetic field causes fluctuations in the NMR frequency, leading to a loss of reproducibility and an effective shortening of the free induction decay after data averaging. Reference deconvolution allows the compensation of field fluctuations via simultaneous measurement of an internal or external reference signal. The technique was applied to compensate the effect of field fluctuations in a resistive electromagnet used for fast field cycling NMR. An external sample was chosen as the reference.     

Nonlinear Simulations of the Bump-on-Tail Instabilities in Tokamak Plasmas

We reproduce nonlinear behaviors,including frequency chirping and mode splitting,referred to as bump-on-tail instabilities.As has been reported in previous works,the generation and motion of phase-space hole-clump pairs in a kinetically driven,dissipative system can result in frequency chirping.We provide examples of frequency chirping,both with and without pure diffusion,in order to illustrate the role of the diffusion effect,which can suppress holes and clumps;Asymmetric frequency chirpings are produced with drag effect,which is essential to enhance holes,and suppress clumps.Although both diffusion and drag effect suppress the clumps,downward sweepings are observed,caused by a complicated interaction of diffusion and drag.In addition,we examine the discrepancies in frequency chirping between marginally unstable,and far from marginally unstable cases,which we elucidate by means of a dissipative system.In addition,mode splitting is also produced via BOT code for a marginal case with large diffusion.     

Electromagnetic Instability in Counterstreaming Collisional Plasmas in a Magnetic Field

The stability of low frequency electromagnetic waves is studied for collisional, counterstreaming plasmas situated in a steady magnetic field. Based on the cold fluid equations, it is found that obliquely propagating waves are unstable when the parallel component of the phase velocity is smaller than the electron streaming velocity. The frequency of the instability is of the order of but always smaller than the ion cyclotron frequency. The growth rate is proportional to the electron-ion collisional frequency.     

Heat Diffusion across a Strong Stochastic Magnetic Field in Tokamak Plasmas

We investigate heat diffusion across a local strong stochastic magnetic field by using eleven low-m perturbed magnetic islands. A maximum stochasticity of 38.82 between two neighboring rational surfaces is attained. The correlation between the effective radial heat conductivity xτ and the ratio of the parallel heat diffusion coefficient to the perpendicular coefficient, χⅡ/χ⊥, is numerically studied and compared with earlier work.     

Low Frequency Electromagnetic Modes in Strongly Magnetized Coupled Plasmas

We consider the effect of Coulomb correlation on the low frequency part of the spectrum of electromagnetic waves propagating in a non‐ideal electron‐ion plasma. The dielectric tensor constructed by means of the theory of moments is employed.     

利用轴向磁化的永磁环制造轴向梯度磁场

首先叙述了由单个轴向磁化环所产生的磁场,并就两个永磁环所产生的纵向磁场进行了分析.对于两个沿同一方向磁化的永磁体环,沿磁环中心线将会产生一个强度较为均匀的轴向磁场.如果两者的磁化方向相反,则在两磁铁间的区域将产生一个纵向的梯度磁场,其磁场强度介于-B₀到+B₀之间.设计制造了一个高梯度的轴向磁场,其磁场梯度为47.2Tm,测量结果与计算结果非常一致.文中还讨论了产生变梯度磁场的方法.由于永磁环所产生的磁场和螺线管的磁场较为相似,磁铁外部空间将有较大的漏场,最后还讨论了屏蔽漏场的问题.     

Instability of Waves in Magnetized Vortex-Like Ion Distribution Dusty Plasmas

A modified Zakharov-Kuznetsov equation for small but finite dustic waces in a magnetized votex-like ion distribution dusty plasma is obtained in this paper.It seems that there are instability for a soliton under higher-order transverse perturbations in this system. There is a certain critical value 4λ0. If the ratio of the wave length of the higher-order perturbations to the width of the soliton is larger than this critical value, the solitary wave is unstable, otherwise it is stable.     

电磁波在磁化等离子体中传播的时域有限差分模拟

基于Z变换形式的时域有限差分法计算公式,模拟了传播方向垂直于磁化磁场的电磁波在磁化等离子体层中的传播.通过离散傅立叶变换,给出了电磁波通过均匀和非均匀磁化等离子体后的反射系数和透射系数随频率的变化关系.还给出了电磁波经过均匀磁化等离子体层后的反射和透射系数和理论值的对比.     

Magnetic Behavior of Ferri-ferromagnetic Alloy in Presence of External Magnetic Field

The magnetic behavior of the mixed ferro-ferrimagnetic alloy with (A_a B_b C_c)_y D structure composed of Ising spins S_A=1, S_B=5/2, S_C=2, and S_D=3/2 in the presence of the external magnetic field is investigated by the use of the effective field theory. The role of concentration b is discussed in this system in detail. Results show that for a=0.4, only when the concentration b is in the region 0.60≥b>0.34 can the ferrimagnetic behavior be seen. Otherwise, the alloy shows ferromagnetic behavior.