Nonlinear Resonant Interaction of Two Longitudinal Waves and a Transverse Wave in a Hot Magnetized Plasma

By Whitham's method of averaged Lagrangian and using Low's form of Lagrangian, coupled mode equations and coupling coefficients are derived for resonant nonlinear interaction of two longitudinal and one transverse wave in a magnetized plasma, in which the later wave propagates along the external uniform magnetic field. The limiting form of these coupling coefficients are obtained when the external magnetic field vanishes.     

Wave-trapped particle interaction in a weak transverse magnetic field

Damping of an electrostatic plasma wave loaded with a small density bunches of trapped electrons and propagating across a weak magnetic field is studied. To describe the time evolution of the wave, simple algebraic equations are derived under some restrictions on the parameters of the physical system. It is shown that the nonlinear frequency shift of the wave due to the presence of the trapped particles plays an important role and must be taken into account in the self-consistent treatment of the wave–particle interaction.     

Relativistic study of electromagnetic electron cyclotron instability based on trapped electrons in kappa-Maxwellian auroral plasmas

The presence of relativistic electrons in the Earth's magnetosphere may excite EMEC waves via resonant interaction. The understanding of EMEC waves induced by such electrons requires relativistic treatment. Therefore, we present here the investigation of EMEC waves based on relativistic trapped electrons represented by kappa-Maxwellian distribution in auroral plasmas. The analytical expressions of real frequency and relativistic growth rate are derived. Our numerical outcomes report that relativistic approximation increases the wave growth and causes reduction in the threshold value of drift velocity of trapped electrons for instability. The wave frequency that corresponds to the maximum growth decreases as we go from nonrelativistic limit to relativistic. The maximum growth increases with the increment in plasma frequency, perpendicular thermal velocity, drift velocity of trapped electrons, and Lorentz factor γ. Moreover, the relativistic effects on maximum growth are more pronounced for smaller values of drift velocity and perpendicular thermal velocity.     

Observation of Raman forward scattering and electron accelerationin the relativistic regime

Raman forward scattering (RFS) is observed in the interaction of a high intensity (>10¹⁸ W/cm²) short pulse (<1 ps) laser with an underdense plasma (n_e~10¹⁹ cm ^-3). Electrons are trapped and accelerated up to 44 MeV by the high-amplitude plasma wave produced by RFS. The laser spectrum is strongly modulated by the interaction, showing sidebands at the plasma frequency. Furthermore, as the quiver velocity of the electrons in the high electric field of the laser beam becomes relativistic, various effects are observed which can be attributed to the variation of electron mass with laser intensity     

激光尾波场横向波破的粒子模拟

用粒子模拟方法，研究激光脉冲的横向宽度有限时对产生激光尾波场和电子加热的影响. 在 纵向和横向有质动力的作用下，电子密度的空间分布形成“马蹄型”的低密度区，这些低密 度区好像运动的透镜，使长脉冲激光自聚焦，而且随着激光的传播，“马蹄型”的曲率越来 越大，直到产生横向波破. 横向波破一方面使得波破时静电场极值远小于波破极限，另一方 面将更多的电子推入加速相位，静电场“俘获”的电子数目大大增加，但最大电子动能明显 减小. 关键词： 尾波场 有质动力 电子俘获 横向波破     

变周期慢波系统内同步问题的研究

由于行波管的工作依赖于其慢波系统中的电子注与沿轴传输交变电磁场之间的相互作用而完成,而这样的相互作用要求沿轴传输的交变电磁场必须与电子注有着近乎同步的速度,所以慢波系统内的同步问题就成了研究行波管的一个很重要的问题.而变周期慢波系统是将一般慢波系统的周期进行变化而形成的,它可以比原周期慢波系统有着更宽的带宽,更高的互作用效率,还可以选择空间谐波.本文分析了变周期慢波系统内的空间谐波,提出了使慢波系统内的一次空间谐波一直与电子注同步所需要满足的原则,最后以变周期折叠波导为例,证明了这个原则. 关键词： 变周期 慢波系统 空间谐波 同步     

Net acceleration of high-energy electrons by net inverse Bremsstrahlung of a laser wave in a uniform magnetic field and a transverse undulating magnetic field

The nonzero net dc force acting on relativistic beam electrons traveling in a uniform magnetic field, a laser wave, and transverse undulating magnetic field (magnetic wiggler) is calculated by using quantum-kinetics in accordance with the correspondence principle. It is found that the average of this force can be as strong as the Lorentz force of the laser wave in an electron energy region beyong energies for free electron lasing, and decreases linearly with the inverse of the electron energy far beyond this energy region.     

Amplification of light during the scattering of a relativistic electron by a nucleus in a moderately strong field of a circularly polarized light wave

The amplification (attenuation) factor of an electromagnetic wave during the scattering of a relativistic electron by a nucleus in a moderately strong field of a circularly polarized electromagnetic wave is studied theoretically. The effect of amplification of an electromagnetic field is discovered in a certain interval of polar angles of the incident electron; this interval of angles essentially depends on the electron energy and the field intensity. It is shown that the amplification of a field attains its maximum for nonrelativistic electrons in the range of medium fields. As the electron energy increases, the amplification decreases and vanishes for ultrarelativistic electrons. An increase in the field intensity for a given electron energy also leads to a slow decrease in the amplification of a field. At high intensities of the wave, the effect of amplification vanishes. It is shown that, in the range of optical frequencies for medium fields (F ～ 10⁶V/cm), the amplification factor of laser light may amount to about μ ～ 10^?1 cm^?1 for sufficiently high-power electron beams.     

Single-stage depressed collectors for gyrotrons

Two 140 GHz gyrotrons with a single-step depressed collector have been operated. The different position of the isolating collector gap in the stray magnetic field causes the electron motion in the retarding region to be in one case adiabatic and in the other case nonadiabatic. The kind of motion within the retarding field influences strongly the behavior of the gyrotron with a depressed collector. In the case of nonadiabatic motion a significant amount of transverse momentum is given to the electrons reflected at the collector potential. This causes the reflected electrons to be trapped between the magnetic mirror and the collector. The electrons escape from the trap by diffusion across the magnetic field to the body of the tube thus contributing to the body current. Despite the high body current there is no observable influence of the collector voltage on the RF output power. In the case of adiabatic motion the reflected electrons do not gain a sufficient amount of transverse momentum to be trapped by the magnetic mirror. They pass the cavity toward the gun and they are trapped between the negative gun potential and the collector. The interaction with the RF field by electrons traveling through the cavity enhances the diffusion in the velocity space thus enabling the trapped electrons to overcome the potential barrier and escape toward the collector. Therefore the body current stays at low values since in this case the reflected electrons do not contribute to it. However, at higher collector voltages a reduction of RF power occurred and some noise in the electron beam was observed     

Competing mechanisms of plasma transport in inhomogeneous configurations with velocity shear: the solar-wind interaction with earth's magnetosphere

Two-dimensional simulations of the Kelvin-Helmholtz instability in an inhomogeneous compressible plasma with a density gradient show that, in a transverse magnetic field configuration, the vortex pairing process and the Rayleigh-Taylor secondary instability compete during the nonlinear evolution of the vortices. Two different regimes exist depending on the value of the density jump across the velocity shear layer. These regimes have different physical signatures that can be crucial for the interpretation of satellite data of the interaction of the solar wind with the magnetospheric plasma.     

Amplification of longitudinal plasma oscillations upon a decrease in plasma concentration

Amplification of plasma oscillations in a homogeneous plasma by reducing its concentration is considered. The frequency of plasma oscillations decreases upon a decrease in the plasma concentration, and the resonant velocity of the plasma electrons, which is equal to the wave phase velocity, also decreases. Due to this, the number of resonant electrons exponentially increases in the equilibrium plasma. Since the energy of plasma oscillations is mainly determined by the contribution of the resonant electrons, this energy also increases exponentially.     

Modulational instability of relativistic ion-acoustic waves in aplasma with trapped electrons

The association between the modified Korteweg-de Vries solitary wave and the modulationally unstable envelope solitary wave in a weakly relativistic unmagnetized plasma with trapped electrons is discussed. The effect of trapped electrons modifies the nonlinearity of the nonlinear Schrodinger equation and gives rise to the propagation of the modulationally unstable ion-acoustic solitary wave. The amplitude of the envelope solitary wave increases while the number of trapped electrons decreases. The velocity of the solitary wave decreases with increasing ionic temperature and increasing particle velocities. The ion oscillation mode, which satisfies the nonlinear dispersion relation, is also derived. The theory is applied to explain space observations of the solar energetic flows in interplanetary space and of the energetic particle events in the Earth's magnetosphere     

Propagation of waves in a multicomponent plasma having charged dust particles

Propagation of both low and high frequency waves in a plasma consisting of electrons, ions, positrons and charged dust particles have been theoretically studied. The characteristics of dust acoustic wave propagating through the plasma has been analysed and the dispersion relation deduced is a generalization of that obtained by previous authors. It is found that nonlinear localization of high frequency electromagnetic field in such a plasma generates magnetic field. This magnetic field is seen to depend on the temperatures of electrons and positrons and also on their equilibrium density ratio. It is suggested that the present model would be applicable to find the magnetic field generation in space plasma.     

Self-consistent structure of a dc discharge with a closed hall current in crossed electric and magnetic fields

A dc glow discharge with a closed Hall current in crossed electric and magnetic fields in helium is investigated. It is shown that the main features of an unmagnetized dc discharge [1] (such as the separation of the discharge into a space charge sheath and a quasineutral plasma, the formation of a cathode fall region and a negative glow, the appearance of a region with a reversed electric field producing a potential well for low-energy electrons and resulting in the formation of a Faraday dark space, and the formation of three pronounced groups of electrons in the electron distribution function) are also retained in a discharge in crossed fields. It is found that the sheath length is almost independent of the magnetic field, while the length of the negative glow region decreases appreciably with increasing magnetic field. The measured electron distribution function agrees well with the nonlocal theory, according to which the current in the Faraday dark space is carried by the intermediate electrons that are not trapped in the potential well and the energies of which are lower than the first excitation energy.     

Stimulated Raman scattering of gaussian laser beam in relativistic plasma

This paper presents an investigation of Stimulated Raman Scattering of gaussian laser beam in relativistic Plasma. The pump beam interacts with a pre-excited electron plasma wave and thereby generate a back-scattered wave. Due to intense laser beam, electron oscillatory velocity becomes comparable to the velocity of light, which modifies the background plasma density profile in a direction transverse to pump beam axis. The relativistic non-linearity due to increase in mass of the electrons effects the incident laser beam, electron plasma wave and back-scattered beam. We have set up the non-linear differential equations for the beam width parameters of the main beam, electron plasma wave, back-scattered wave and derived SRS back-reflectivity by taking full non-linear part of the dielectric constant of relativistic plasma with the help of moment theory approach. It is observed from the analysis that self-focusing of the pump beam greatly affects the SRS reflectivity, which plays a significant role in laser induced fusion.     

Enhancement of the nonlinear acoustoelectric interaction in a photoexcited plasma in a quantum well

Nonlinear interaction of an intense surface acoustic wave (SAW) with a 2D electron-hole plasma generated by light in a semiconductor quantum well near a piezoelectric crystal is investigated. It is shown that, in a strongly nonlinear regime, the acoustoelectric interaction is enhanced because of the accumulation of carriers in the field of an intense SAW. In addition, in a strongly nonlinear regime, the dissipation of the acoustic wave energy increases and the sound velocity decreases. These dependences fundamentally differ from those observed in a unipolar plasma. For high sound intensities, analytical results are obtained.     

Field theory of dielectric Cherenkov maser

The effect of three-dimensional perturbed velocity and three-dimensional perturbed current density on the beam-wave interaction of dielectric Cherenkov maser is analysed by use of the self-consistent linear field theory. Three distinct cases are considered. First, the propagation of the electron beam in an annular dielectric liner enclosed by a loss-free conducting wall is investigated. The dispersion equation and the simultaneous condition of the beam-wave interaction are derived. It's clearly shown that the instability of the interaction results from the coupling of the TM mode in the dielectric lined slow-wave waveguide to the beam mode via the electron beam. And the coupling is proportional to the density of the beam. The growth rate of the wave produced by the electron beam are obtained. Then, the case of a relativistic electron beam guided by a longitudinal magnetic field in the same slow-wave structure is examined. The motion of electrons could be approximated to be one-dimensional when the simultaneous condition of the beam-wave interaction of dielectric Cherenkov maser is satisfied. Finally, the effect of the background plasma on the instability of the beam-wave interaction is studied.This work is supported by National Natural Science Foundation of China.     

磁化等离子体中逃逸电子的临界速度

根据等离子体动力论,分析了在磁化等离子体中逃逸电子的临界速度,并在托卡马克参数下作了数值计算。计算表明,有磁场时,逃逸电子所受到的摩擦力,在纵向速度较大时比无磁场时的为大,这相应于逃逸电子临界速度的提高,因而高能的逃逸电子也较难产生。当磁场增大时,摩擦力略有减小。在纵向速度较高时,逃逸电子的横向速度分量对临界速度的影响较明显,横向速度越大,临界速度也越大。 关键词：     

Conditions for the existence of a positively charged structure in a Penning discharge

An analytical model is developed for the high-current form of a low-pressure glow discharge in a magnetic field. Expressions are derived for the critical magnetic induction and critical pressure, below which it becomes impossible for this form of discharge to exist. It is shown that the transition from the high-voltage form to the high-current form of discharge with increasing pressure is not attributable to an increase in the ionization rate, but to an increase in the drift velocity of plasma electrons across the magnetic field. Estimates based on the expressions derived in the article agree in order of magnitude with the experimental data. It is shown that the region in which discharge exists can change considerably in the presence of electron emission. Zh. Tekh. Fiz. 68, 56–63 (July 1998)     

Evolution of a langmuir wave in a weakly inhomogeneous plasma with a positive concentration gradient

Spatial evolution of a Langmuir wave excited by external sources in a weakly inhomogeneous electron plasma without external sources is considered for a small positive gradient of the plasma concentration in the direction of propagation of the wave. At the first state of the evolution, the dispersion of the wave is close to linear. When the phase velocity is doubled, the second stage of the evolution begins. The wave loses its individuality and becomes a hybrid of two waves. Its profile acquires the shape of an alternating sequence of fragments of these waves. The wave dispersion is determined by the dispersion of each fragment. In the course of evolution, the spacing between the equilibrium values of the wave fragments increases; as a result, the wave decays into two waves, which are also loaded by trapped electrons. Prior to decay, the humps of the wave become steeper; as a result, at the instant of the decay, the wave is transformed into a sequence of solitons with different polarities.