非均匀尘埃等离子体中孤子的传播

运用约化摄动法研究了非均匀尘埃等离子体中孤子的传播情况. 在低阶近似下, 对于小的、但有限振幅的长波振动, 当分界面不连续变化时,孤子在不连续点的反射波与透射波均可由 KdV 方程来描述, 并给出了低阶近似情况下, 对于小的、但有限振幅的长波振动, 当入射波为单孤子时, 反射孤子与透射孤子的个数及其大小;当分界面是有限长度并连续变化时,对于小的、但有限振幅的长波振动, 尘埃声孤波由KdV型方程来描述,并由此给出了准孤子振幅、传播速度等参量在传播过程中的变化. 关键词： 尘埃等离子体 孤子 KdV方程 约化摄动法     

Second-harmonic generation of electron-bernstein waves in an inhomogeneous plasma

In the injection of electron-Bernstein waves (EBW) into a plasma, proposed for plasma heating and current drive in over-dense plasma, conversion of the fundamental to its second harmonic is predicted analytically and observed in computations. The mechanism is traced to the existence of locations where one can have both wave number and frequency matching between the fundamental and its harmonic. Further, at such locations, the second harmonic commonly has minimal group velocity, and this allows the amplitude of the second harmonic to build to values exceeding that of the fundamental at power levels less than anticipated in experiments. The second-harmonic power can then be deposited at half-harmonic resonances of the original wave, often far from the desired location of energy deposition. Estimates for the power at which this is significant are given.     

Electron acceleration during the breaking of an intense plasma wave in an inhomogeneous plasma

We investigate the dynamics of the electron acceleration when an intense plasma wave breaks near resonance at the plasma frequency (focus) in an inhomogeneous magnetized plasma. The breaking threshold has been determined. We compare our experimental dependences of the current and energy of fast electrons on the intensity of the incident wave at various times with theoretical estimates. We show that when the breaking threshold is significantly exceeded, up to 50% of the electrons at plasma resonance are captured and accelerated by the wave.     

Magnetic field contribution to soliton propagation and reflection in an inhomogeneous plasma

The propagation and reflection characteristics of an ion acoustic soliton are studied in an inhomogeneous plasma through two coupled equations of the KdV family, and the contribution of external static magnetic field is evaluated. The incident and reflected solitons behave oppositely with the angle ψ   between the directions of magnetic field and the wave propagation. Two cases of ω_pi>Ωi${\omega }_{pi}>{\Omega }_i$ and ω_pi<Ωi${\omega }_{pi}<{\Omega }_i$ are examined, where ω_pi${\omega }_{pi}$ is the ion plasma frequency and Ωi${\Omega }_i$ is the ion gyrofrequency. It is found that the soliton gets reflected more strongly when the condition ω_pi>Ωi${\omega }_{pi}>{\Omega }_i$ is achieved in the plasma. The effect of magnetic field is found to be more pronounced on the reflected soliton.     

Nonlinear wave damping on an electron hole in a weakly inhomogeneous plasma

Nonlinear damping of the Langmuir wave in a weakly inhomogeneous plasma with a negative concentration gradient is considered. For phase velocities close to the thermal velocity of electrons, their dispersion strongly differs from the linear one and cannot be taken into account by means of a small correction to the linear dispersion law. Based on the energy balance and nonlinear dispersion equations, a dependence of the wave amplitude on its phase velocity is established together with the limiting phase velocity at which the wave is completely damped.     

Nonlinear propagation of relativistically intense electromagnetic waves in a collisionless plasma

We discuss the nonlinear propagation of relativistically intense electromagnetic waves into collisionless plasmas with special emphasis on one dimensional plane wave solutions of the propagating, standing and modulated types. These solutions exhibit a rich variety of phenomena associated with relativistic electron mass variation and coupling between transverse electromagnetic and longitudinal fields. They have important applications to problems of laser propagation, self-focusing in overdense plasmas, particle and photon acceleration and to electromagnetic radiation around pulsars.     

X射线在折射率连续变化等离子体介质中的传播

从Maxwell方程出发,得到了X射线光束在非均匀等离子体介质中传播的类衍射积分解,并从理论和数值模拟上着重讨论了折射率梯度效应对光束参数的影响。结果表明,在等离子体电子密度分布较高的区域,梯度效应明显,它直接影响光束的光强分布、衍射效应和光束的偏转程度。     

X射线在折射率连续变化等离子体介质中的传播

 从Maxwell方程出发，得到了X射线光束在非均匀等离子体介质中传播的类衍射积分解，并从理论和数值模拟上着重讨论了折射率梯度效应对光束参数的影响。结果表明，在等离子体电子密度分布较高的区域，梯度效应明显，它直接影响光束的光强分布、衍射效应和光束的偏转程度。     

On the quasistatic part of the effective-dielectric-constant tensor of collisionless randomly inhomogeneous plasma

The components of the quasistatic part of the effective-dielectric-constant tensor of a collisionless randomly inhomogeneous plasma are calculated, including those near plasma resonances. In the case of an isotropic plasma, the inhomogeneities are assumed to be arbitrarily oriented ellipsoids with arbitrary anisotropy indices. In the case of an anisotropic plasma, the inhomogeneities are assumed to be infinitely extended along the external magnetic field. A test of such an approximation is formulated, and its use is justified. The formulas obtained should be used for correct determination of the effective-dielectric-constant tensor.Scientific-Research Radio-Physics Institute. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 37, No. 2, pp. 183–193, February, 1994.     

Second harmonic generation of high power Cosh-Gaussian beam in cold collisionless plasma

The purpose of this study is to explore the second harmonic generation (SHG) of a high power Cosh-Gaussian beam in cold collisionless plasma. The ponderomotive force causes carrier redistribution from high field to low field region in presence of a Cosh-Gaussian beam thereby producing density gradients in the transverse direction. The density gradients so produced the results in electron plasma wave (EPW) generation at the frequency of the input beam. The EPW interacts with the input beam resulting in the production of 2nd harmonics. WKB and paraxial approximations are employed for obtaining the 2nd order differential equation describing the behavior of the beam's spot size against normalized distance. The impact of well-established laser-plasma parameters on the behavior of the beam's spot size and SHG yield are also analyzed. The focusing behavior of the beam and SHG yield is enhanced with an increase in the density of plasma, the radius of the beam and the decentred parameter, and with a decrease in the intensity of the beam. The results of the current problem are really helpful for complete information of laser-plasma interaction physics.     

Electron kinetics in collisionless shock waves

We study the kinetic model of the formation of the energy spectrum of nonthermal electrons near the front of a quasilongitudinal, supercritical, collisionless shock wave. Nonresonant interactions of the electrons and the fluctuations generated by kinetic instabilities of the ions in the transition region inside the shock front play the main role in the heating and preacceleration of electrons. We calculate the electron energy spectrum in the vicinity of the shock wave and show that the heating and preacceleration of electrons occur on a scale of the order of several hundred ion inertial lengths in the vicinity of the viscous discontinuity. Although the electron distribution function is significantly nonequilibrium near the shock front, its low-energy part can be approximated by a Maxwellian distribution. The effective electron temperature T _eff ² behind the front, obtained in this manner, increases with the Mach number of the shock wave slower than it would if it followed the Hugoniot adiabat. We determine the condition under which the electron heating is ineffective but the electrons are effectively accelerated to high energies. The high-energy asymptotic behavior of the distribution function is that of a power law, with the exponent determined by the total compression ratio of the plasma, as in the case of acceleration by the first-order Fermi mechanism. The model is used to describe the case (important for applications) of acceleration of electrons by shock waves with large total Mach numbers, with the structure of these waves modified by the nonlinear interaction of nonthermal ions and consisting of an extended prefront with a smooth variation of the macroscopic parameters and a viscous discontinuity in speed with a moderate value of the Mach number. Zh. éksp. Teor. Fiz. 115, 846–864 (March 1999)     

Absence of shocks in an initially dilute collisionless plasma

The Cauchy Problem for the relativistic Vlasov-Maxwell equations is studied in three space dimensions. It is assumed that the initial data satisfy the required constraints and have compact support. If in addition the data have sufficiently smallC ² norm, then a uniqueC ¹ solution to this system is shown to exist on all of spacetime.Research supported in part by NSF DMS 85-20662 and NSF DMS 84-20957     

Sound propagation above an inhomogeneous impedance plane

Boundary integral equation (BIE) methods are described for the prediction of sound propagation, in particular from a line source, over a flat plane of inhomogeneous impedance. Approximate methods, which satisfy reciprocity, for the calculation of the wave field over a two-impedance plane are proposed. These approximations, applied to propagation from a line source, give results agreeing well with those of the BIE method. When they are applied to propagation from a point source, agreement with experiment is shown.     

Solitons in collisionless cold plasma

The relativistic nonlinear self-consistent equations for a collisionless plasma with stationary ions are transformed into a form appropriate for finding exact analytic solutions. It is shown that for an axial system with planar geometry, the two-dimensional stationary equations for this system can be reduced to the sh-Gordon equation. The exact solution of this equation describing the charge-density equilibrium configuration is obtained, the solution having sharp transverse boundaries and a soliton form in longitudinal direction. The generalization to the nonstationary case is considered in an perturbative approach.     

Electron plasma waves generation in suddenly created isotropicplasma

Electron plasma waves excitation in suddenly created isotropic plasma as a result of weak nonlinear interaction of linearly polarized plane electromagnetic (EM) wave and electrons has been considered. By the use of standard perturbation method the problem is solved in closed form for the case of a simple harmonic source EM wave. The appearance of the second harmonic and time independent modes have been demonstrated. The efficiency of excitation of these modes is possible to control by varying the frequency of the source wave     

非均匀量子等离子体中的非线性波

本文探讨具有温度和密度梯度的非均匀量子等离子体系统, 获得了该系统在离子与中子碰撞频率较低情况下的二维非线性流体动力学方程． 求得了非均匀量子等离子体中的电势的冲击、爆炸和旋涡解．分析讨论了在致密天体物理环境中静电势的变化, 结果表明电势的冲击波的幅度和爆炸波的宽度,都随密度的增大(即随无维量子参量的减小)而增大, 但随漂移速度的增大(即随密度和温度梯度的增大)而减小; 静电势随时空相位的增大而趋向于稳定值, 系统最后达到稳定的状态． 旋涡解表明,旋涡静电势的时空分布呈现稳定的周期性的旋涡流．