Driven spin wave modes in XY ferromagnet: non-equilibrium phase transition

The dynamical responses of XY ferromagnet driven by linearly polarised propagating and standing magnetic field wave have been studied by Monte Carlo simulation in three dimensions. In the case of propagating magnetic field wave (with specified amplitude, frequency and the wavelength), the low temperature dynamical mode is a propagating spin wave and the system becomes structureless (or random) in the high temperature. A dynamical symmetry breaking phase transition is observed at a finite (non-zero) temperature. This symmetry breaking is confirmed by studying the statistical distribution of the angle of the spin vector. The dynamic non-equilibrium transition temperature was found to decrease as the amplitude of the propagating magnetic field wave increased. A comprehensive phase boundary is drawn in the plane formed by temperature and amplitude of propagating field wave. The phase boundary was observed to shrink (in the low temperature side) for longer wavelength of the propagating magnetic wave. In the case of standing magnetic field wave, the low temperature excitation is a standing spin wave which becomes structureless (or random) in the high temperature. Here also, like the case of propagating magnetic wave, a dynamical symmetry breaking non-equilibrium phase transition was observed. A comprehensive phase boundary was drawn. Unlike the case of propagating magnetic wave, the phase boundary does not show any systematic variation with the wavelength of the standing magnetic field wave. In the limit of vanishingly small amplitude of the field, the phase boundaries approach the recent Monte Carlo estimate of equilibrium transition temperature.     

Propagation Characteristics of Wave Packet in Non-Uniform Magnetic Fields

Experimental observations on a wave packet in a positive column of helium discharge with magnetic fields are reported. The wave packet is a kind of ionization wave and is created by applying voltage pulses to a mesh grid. When an axial non-uniform magnetic field is applied to a positive column, the plasma parameters change inhomogeneously near the magnetic coil. So various characteristics (amplitude, frequency, wavelength and so on) of the wave packet are changed at the both sides of the coil. The wavelength of the wave making up the wave packet varies continuously with a magnetic field. On the contrary, its amplitude and frequency vary remarkable near the magnetic coil, as a strong magnetic field is applied.     

Magnetic instability in superconductivity

Possible magnetic ordering in the magnetic superconductors is investigated by calculating the wave number dependent susceptibility χ(q) in the superconducting state for (i) clean superconductor, (ii-1) dirty superconductor with weak spin-orbit scattering and (ii-2) dirty superconductor with strong spin-orbit scattering. The wave vector q_max which maximizes χ(q) is estimated for each cases and it is pointed out that the possible magnetic ordering in superconducting state is the spin density wave with the wave number q_max.     

Pulsed magnetic resonance as a probe of longitudinal spin waves and magnetic second sound

Under appropriate conditions, longitudinal spin waves and spin wave second sound, a magnetic temperature wave, can be observed in quantum liquids and solid using pulsed magnetic resonance. A “hole-burning” experiment yields directly the spectrum ω(k) of the propagating magnetic wave.     

Study on the polarization properties of electromagnetic waves with arbitrary magnetic declination in magnetized plasma

The polarization characteristics of oblique incidence electromagnetic waves in magnetized cold plasma layer are studied using the finite-difference time-domain (FDTD) method based on the trapezoidal recursive convolution (TRC) technology. The TRC-FDTD formulations are derived in detail and are confirmed by computing the reflection and transmission coefficients for the elliptically polarized wave through a magnetized cold plasma slab with arbitrary magnetic direction. Particularly, when the propagation direction of the EM wave is parallel to the magnetic direction, the right-circular-polarized and left-circular-polarized wave should be considered. When the propagation direction of the EM wave is perpendicular to the magnetic direction, the ordinary polarized wave and extraordinary polarized wave should be considered.     

Wave propagation in viscoelastic single-walled carbon nanotubes with surface effect under magnetic field based on nonlocal strain gradient theory

The governing equation of wave motion of viscoelastic SWCNTs (single-walled carbon nanotubes) with surface effect under magnetic field is formulated on the basis of the nonlocal strain gradient theory. Based on the formulated equation of wave motion, the closed-form dispersion relation between the wave frequency (or phase velocity) and the wave number is derived. It is found that the size-dependent effects on the phase velocity may be ignored at low wave numbers, however, is significant at high wave numbers. Phase velocity can increase by decreasing damping or increasing the intensity of magnetic field. The damping ratio considering surface effect is larger than that without considering surface effect. Damping ratio can increase by increasing damping, increasing wave number, or decreasing the intensity of magnetic field.     

磁化分层等离子体中电磁波传播特性研究

采用混合矩阵法,分析了磁化分层等离子鞘套对斜入射电磁波传播特性的影响,分别计算了不同入射角以及外加磁场下电磁波透射系数和极化特性的变化。以GPS导航信号右旋圆极化波(RCP)为例,研究了磁场、电子密度对电磁波右旋圆极化特性的影响。结果表明,外加磁场能够使右旋圆极化波在等离子体中的阻带向高频方向移动,此外,外加磁场能在一定程度上改善斜入射是圆极化波的极化特性,有利于GPS信号接收。     

Supersonic Shock Wave with Landau Quantization in a Relativistic Degenerate Plasma

A three-dimensional(3D)BurgersJ equation adopting perturbative methodology is derived to study the evolution of a shock wave with Landau quantized magnetic field in relativistic quantum plasma.The characteristics of a shock wave in such a plasma under the influence of magnetic quantization,relativistic parameter and degenerate electron density are studied with assistance of steady state solution.The magnetic field has a noteworthy control,especially on the shock wave's amplitude in the lower range of the electron density,whereas the amplitude in the higher range of the electron density reduces remarkably.The rate of increase of shock wave potential is much higher(lower)with a magnetic Held in the lower(higher)range of electron density.With the relativistic factor,the shock wave's amplitude increases significantly and the rate of increase is higher(lower)for lower(higher)electron density.The combined effect of the increase of relativistic factor and the magnetic field on the strength of the shock wave,results in the highest value of the wave potential in the lower range of the degenerate electron density.     

Effect of the direction of biasing field on magnetostatic volume wave delays

An investigation of the effect of the direction of a dc biasing field on the magnetostatic volume wave delays in YIG sandwiched between two ground planes has been made. Specifically, the magnetic field has been assumed to be arbitrary in three planes: (a) forward volume wave to backward volume plane; (b) forward volume wave to surface wave plane; (c) backward volume wave to surface wave plane. A general dispersion relation has been derived. The numerical results indicate that delays can be controlled by the direction of the dc magnetic field. The effect of the thickness of the dielectric on the delay characteristics of magnetostatic backward volume waves has also been studied. The present study shows that a suitable filter can be designed, whose bandwidth may be varied by rotating the direction of the magnetic field.     

A full wave model of high-harmonic EMIC wave propagation in sheared magnetic fields

ABSTRACT

A new dispersion relation, with finite Larmor orbit effects, for oblique propagating electromagnetic ion cyclotron (EMIC) waves in a magnetized plasma medium, is derived including the magnetic shear effect. The approximate, yet accurate, dispersion relation is used to implement the ray tracing model. A parabolic magnetic field is considered to model the geomagnetic field in the magnetosphere. Energetic protons are also considered as resonant particles. The propagation characteristics of EMIC waves in the vicinity of the ion cyclotron resonances are investigated in some detail. The results reveal adiabatic oscillating motion for wave and magnetic field fluctuations where high harmonics limit the wave damping and confines the magnetic fluctuations. For inward propagating EMIC waves we find (1) turning points which depend on the wave launch position, and (2) wave trapped areas playing a role in quasi-coherent wave-particle interaction in agreement with the observational and theoretical studies. This wave trapping is an effective process for particle acceleration in the context of space plasmas.     

磁场对螺旋波等离子体波和能量吸收影响的数值研究

本文考察在径向电子数密度呈抛物形分布的情况下,外加稳恒磁场,射频通过螺旋波天线在等离子体中激发电磁波的传播性质.采用线性扰动波假设,数值求解Maxwell方程组,得到80—800 G(1 G=10-4T)磁场条件下等离子体中径向电、磁场强度及能量沉积密度的分布情形.计算结果表明,磁场增大(80→800G)时,螺旋波受到的阻尼较小,可深入等离子体传播;Trivelpiece-Gould(TG)波受到的阻尼增大,在等离子体-真空边界处衰减增强;整体的能量吸收向边界集中.磁感应强度小于100 G时,TG波可深入主等离子体区传播,等离子体径向能量吸收相对均匀.     

柱面内爆磁通量压缩实验中的磁扩散过程

利用一维磁流体力学程序MC11D,对套筒材料为不锈钢的柱面内爆磁通量压缩实验进行了数值模拟,研究了其中的磁扩散过程。计算结果表明:当套筒空腔中的磁场被压缩到350 T左右时,峭面磁扩散波开始形成,磁扩散波的波前从套筒内壁开始以0.75 km/s的平均速度向外快速推进,给磁场的压缩带来了不利影响;随着套筒内壁温度迅速升高,内壁附近会形成一个电阻率仅有0.3 mcm左右的等离子体保护层,又极大地减缓了空腔磁场向套筒中扩散的速度。在磁压缩过程中,峭面磁扩散波和等离子体层对于空腔磁场的扩散起着相反的作用,两者在发展的过程中相互竞争,在不同的阶段分别起着主导作用。     

柱面内爆磁通量压缩实验中的磁扩散过程

利用一维磁流体力学程序MC11D,对套筒材料为不锈钢的柱面内爆磁通量压缩实验进行了数值模拟,研究了其中的磁扩散过程。计算结果表明:当套筒空腔中的磁场被压缩到350 T左右时,峭面磁扩散波开始形成,磁扩散波的波前从套筒内壁开始以0.75 km/s的平均速度向外快速推进,给磁场的压缩带来了不利影响;随着套筒内壁温度迅速升高,内壁附近会形成一个电阻率仅有0.3 mcm左右的等离子体保护层,又极大地减缓了空腔磁场向套筒中扩散的速度。在磁压缩过程中,峭面磁扩散波和等离子体层对于空腔磁场的扩散起着相反的作用,两者在发展的过程中相互竞争,在不同的阶段分别起着主导作用。     

Quantum-kinetic calculation for net acceleration of high-energy electrons by a transverse undulating magnetic field and an electromagnetic wave

The average force acting on a highly relativistic electron beam traveling in a laser wave and a transverse undulating magnetic field (magnetic wiggler) is calculated using quantum kinetics. The quantum-kinetic calculation shows that the net dc force due to net inverse bremsstrahlung in the magnetic wiggler (“inverse free electron lasing”) increases linearly with the beam energy, and can be greater than the Lorentz force of the laser wave.     

Indicatrices of magnetostatic surface waves

Indicatrices (isofrequency curves) of magnetostatic surface waves are studied with allowance for wave attenuation. A bias magnetic field is applied tangentially to a ferrite film. Arbitrary angles between the bias magnetic field and the wave vector are examined.     

磁性薄膜畴壁短波长自旋波模式激发

研究约束在磁性薄膜畴壁中的自旋波Ｗｉｎｔｅｒ模式及其激励方式．用坡莫合金磁性栅格将高频均匀磁场转换成与自旋波Ｗｉｎｔｅｒ模式在时间频率和空间波长都匹配的磁场，从而实现相互间的有效耦合．采用锁相放大技术观测到了几百兆赫自旋波Ｗｉｎｔｅｒ模式微分吸收峰 关键词：     

时变磁化等离子体的LTJEC-FDTD方法研究

基于拉普拉斯变换的电流密度卷积技术（LTJEC）,构造了时变磁化等离子体的新型时域有限差分方法（LTJEC-FDTD）。借助于高斯脉冲在磁化等离子体中的传播实例,验证了LTJEC-FDTD算法的准确性及高效性。进一步,研究了Whistler波在一维时变磁化等离子体中的具体传播特性。结果表明,当离子体频率随时间指数衰减后,输出波的频率上升、极化方式不变,而电场增强、磁场减弱。同时,通过优化磁化等离子体参数,可进一步提高Whistler波的输出频率,获得了频率为300 GHz的圆极化太赫兹波。研究结果可为利用磁化等离子体产生太赫兹波源提供相关的技术支持。     

相对论磁化运动等离子体的介电张量

 定义了相对论磁化运动等离子体(MMP)的物理模型。利用微扰理论导出了系统的介电张量，研究发现，MMP具有完全不同于静态磁化等离子体介电张量的形式。对电磁波沿轴向传播的情况进行了数值模拟计算，结果表明，系统的共振频率随等离子体密度的增加而非线性增加，在相同的条件下，右旋波的共振频率高于左旋波的共振频率。对于传播的右旋电磁波，增加纵向磁场，共振频率提高，而对于左旋电磁波，增加纵向磁场，共振频率降低。