Wave propagation in a rarefied plasma with finite Larmor radius

Wave propagation in a rarefied two-component plasma immersed in a uniform constant magnetic field has been discussed wherein the plasma pressure is assumed to be anisotropic owing to finite Larmor radius effect. It is shown that, for propagation along the external magnetic field, there exist two modes of wave propagation, namely, the gravitational mode and the hydromagnetic mode. The former is found to be independent of the magnetic field and hence of the Larmor radius, while the latter is appreciably influenced by the finite Larmor radius. On the other hand, for transverse propagation, there are three modes of wave propagation viz. the ion-sound mode, the electron-sound mode and the electromagnetic mode. It is shown that only the lowfrequency ion-sound mode is affected by the finite Larmor radius.     

Effect of multiple ion reflections on the structure of an ion-sound shock wave

It is shown that multiple ion reflection, arising as a result of collisional dissipation, from a shock front can produce an ion-sound shock wave with an arbitrarily large Mach number. For an exponentially small number of reflected ions, the ion-sound shock wave “degenerates” into a collisionless quasishock wave. The comparative role of viscosity and sound dispersion with different initial nonisothermality of the plasma is discussed. Zh. Tekh. Fiz. 69, 52–56 (December 1999)     

Influence of anisotropy on the structure of an ion-sound wave

We study the influence of magnetic field on the ion-sound disturbance of a weakly ionized plasma ahead of a strong shock wave of the neutral component. Different regimes (subsonic, sonic, and supersonic) are studied. Main attention is paid to the case of formation of a discontinuous field in the plasma. Radiophysical Research Institute, St. Petersburg University, St. Petersburg, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 42, No. 2, pp. 120–128, February 1999.     

Low-frequency longitudinal oscillations in a plasma with a relativistic electron component

Ion-sound oscillations in a three-dimensional plasma with relativistic electron component are studied. It is established that in this case ion-sound oscillations can exist only at electron and ion temperatures much less than the rest mass of the ions. In particular, it is shown that for an electron-positron plasma at relativistic temperatures ion-sound is impossible. The problem of ion-sound excitation by a charged particle beam is considered. Corresponding increments in beam instability are calculated.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 24–27, December, 1985.     

Dissipation of strong Langmuir turbulence in nonisothermal non-Maxwellian plasma

The regime of strong Langmuir turbulence characterized by the plasma nonisothermality and by the presence of an appreciable non-Maxwellian hot-electron component was experimentally studied. Turbulence was excited in the preliminary produced plasma by the relativistic electron beam. Thomson scattering of laser IR radiation served as the main diagnostic method. The spatial spectra of the Langmuir turbulence and of the attendant ion-sound turbulence were studied using Thomson collective scattering. Thomson incoherent scattering was used for studying the plasma electron distribution function and searching for the local dips of plasma density. Stark spectroscopy of turbulent microfields and the method of observation of plasma radiation at the double plasma frequency were also used. Based on the experimental data, the mechanism of Langmuir oscillation damping by plasma electrons was analyzed. The Langmuir wave conversion induced by the ion-sound turbulence is the most probable channel for energy transfer from the turbulence to plasma electrons, the low-frequency fluctuations being the direct consequence of the strong Langmuir turbulence.     

Two-tone ion-acoustic waves in degenerate quantum plasma

Ion-acoustic waves (IAWs) in a quantum electron-ion plasma with degenerate components are theoretically investigated using a system of quantum equations of gas dynamics that allow for the quantum-size character of the object (Bohm’s quantum force is included in the equation of motion) and the Pauli exclusion principle (equations of state for degenerate Fermi gases of electrons and ions are used). Linear analysis and numerical solution of equations yielded an identical qualitative result: periodic IAWs in a quantum electron-ion plasma are always a superposition of two waves with equal phase velocities but different wavelengths. The high-frequency component of the IAW is identified with free quantum oscillations of ions. A solution in the form of an ion-sound soliton with free quantum oscillations of ions superposed on its profile is also found.     

On the Existence of Hypersonic Electrostatic Solitons (Estimation of Limiting Mach Numbers of Ion-Sound Solitons in a Warm Plasma)

Journal of Experimental and Theoretical Physics - We develop a nonlinear theory of ion-sound waves in a collisionless warm electron–ion plasma. The theory is based on analysis of the Sagdeev...     

Feasibility of a plasma-filled inverse free electron laseraccelerator

A high power millimeter (mm) wave, in the presence of a magnetic wiggler, produces a large longitudinal ponderomotive force that can accelerate electrons. When a plasma of density n~n_cr, where n _cr is critical density, is introduced in the interaction region, the ponderomotive force resonantly drives a plasma wave that accelerates electrons to higher energies. However, propagation of the mm wave requires a guide magnetic field; O-mode requiring less field than the X-mode. The plasma wave in this situation goes over to the upper hybrid (UH) mode. A parabolic plasma density profile with minimum on axis provides guiding for the mm wave as well as the UH wave, the latter being more strongly localized than the former. The UH wave, for typical parameters, can accelerate electrons to several tens of megaelectronvolts     

Structural ion-sound plasma turbulence as a self-similar random process

It is shown that the experimentally investigated structural ion-sound plasma turbulence is a self-similar stationary random process. The self-similarity parameter is determined by two temporal laws: the nonrandom character of the appearance of nonlinear structures (nonlinear ion-sound solitons) in the plasma, and the nonlinear interaction between them. As the distance from the threshold of the ion-sound current instability increases, the self-similar random process approaches a Gaussian random process, but this limit has not been attained experimentally. The possibility of recording superlong time series of the fluctuations of the signal of the plasma process and processing of the time series by the R/S analysis method has made it possible to prove self-similarity of the plasma structural turbulence. Pis’ma Zh. éksp. Teor. Fiz. 70, No. 3, 203–208 (10 August 1999)     

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分析了电磁波以任意角度入射到有限磁场中的激光等离子体通道天线(LPCA)时的电磁散射特性。根据LPCA的工作原理建立了其电磁分析模型,推导出广义柱坐标系下各向异性磁化等离子体中纵向分量所满足的波动方程和纵向场与横向场的关系,得到LPCA和周围媒质中的电磁场,利用边界切向电磁场连续,得出了散射系数方程。通过计算实例,将结果与文献结果比较,吻合较好。该研究结果预期可应用于高功率微波武器系统的研究。     

Real-time measurement of wave components and intensity in a beam in the presence of a near field

A method is described by which the individual flexural wave components in a beam can be measured in real time. Attention is focussed on the case in which two propagating waves and a single near-field wave exist, although the case of two near fields is also considered. Because the presence of the near field is included, the measurements can be taken close to the force, boundary or discontinuity from which the near field arises. Potential applications include intensity measurement, active control and adaptive-passive vibration control.The wave components are measured by digitally filtering and combining the outputs of an array of sensors, with an array of three, equally spaced sensors being considered in detail. The filters are designed in the frequency domain using a wave decomposition approach, and implemented in the time domain as FIR filters. Design, implementation and performance issues are discussed and an experimental implementation described. It is seen that accurate estimates of the amplitudes of the wave components can be obtained using FIR filters of moderate order, and that the method is relatively insensitive to sensor miscalibration and measurement noise.     

Optical forces from an evanescent wave on a magnetodielectric small particle

We report the first study on the optical force exerted by an evanescent wave on a small sphere with both electric and magnetic responses to the incident field, immersed in an arbitrary nondissipative medium. New expressions and effects from their gradient, radiation pressure, and curl components are obtained owing to the particle induced electric and magnetic dipoles, as well as to their mutual interaction. We predict possible dramatic changes in the force depending on the host medium, the polarization, and the nature of the surface wave.     

Generation of harmonics of intense laser radiation in a transparent collisionless plasma

The spectral composition of a relativistically strong uniform nonlinear electromagnetic wave in a transparent collisionless plasma is analyzed. The vortex and potential components of the wave field are shown to contain only odd and even harmonics, respectively; in a transparent plasma, the wave remains quasi-monochromatic, since the intensities of the harmonics decrease exponentially with increasing harmonic number. An equation that includes diffraction effects is derived to describe the propagation of wavepackets. The results obtained are compared with experimental data.     

Repetitive formation of propagating wave packets in an anomalously resistive phase of HV straight discharge

UHF fluctuations in the plasma potential in the quasi-stationary phase of current limitation were picked up by three capacitively-coupled probes, arranged axially across the midplane. Cross-correlation measurements between the adjacent probes showed the propagation of wave packets with a velocity of nearly 4 C_S = 9 × 10⁷ cm/s, C_S being the ion-sound velocity.     

Ponderomotive effects in intense pumping wave action on electron and plasma bunches

Ponderomotive effects that arise when an intense plane pumping wave acts on low-concentration electron and plasma bunches are theoretically studied within the framework of a one-dimensional model. Using the Lagrange variables, an electron (plasma) bunch under the action of a pumping field can be represented as a gas comprising macroparticles with ponderomotive and Coulomb interactions. The ponderomotive force at small interparticle distances is attractive, that is, directed oppositely to the Coulomb force; it cannot, however, completely balance the latter. The constructed model is used to study superradiance, which arises when an intense pumping wave acts on an extended electron bunch. Radiation is then scattered in the form of narrow pulses whose amplitude is proportional to the total number of particles in the bunch. In addition, we describe acceleration of a neutral plasma layer, narrow on the wavelength scale, in the field of an intense wave and radiation field-induced partial contraction of an electron bunch with an incompletely compensated charge.     

Freak waves in laboratory and space plasmas

Generation of large-amplitude short-lived wave groups from small-amplitude initial perturbations in plasmas is discussed. Two particular wave modes existing in plasmas are considered. The first one is the ion-sound wave. In a plasmas with negative ions it is described by the Gardner equation when the negative ion concentration is close to critical. The results of numerical solution of the Gardner equation with the modulationally unstable initial condition are presented. These results clearly show the possibility of generation of freak ion-acoustic waves due to the modulational instability. The second wave mode is the Alfvén wave. When this wave propagates at a small angle with respect to the equilibrium magnetic field, and its wave length is comparable with the ion inertia length, it is described by the DNLS equation. Studying the evolution of an initial perturbation using the linearized DNLS equation shows that the generation of freak Alfvén waves is possible due to linear dispersive focusing. The numerical solution of the DNLS equation reveals that the nonlinear dispersive focusing can also produce freak Alfvén waves.     

Evolution of an intense elliptically polarized electromagnetic wave in underdense plasmas

An elliptically polarized electromagnetic wave in an underdense plasma acquires a longitudinal component of the electric field which oscillates as even harmonics of the fundamental frequency. The phase shift between transverse field components and the wave amplitudes exhibit nonlinear oscillations.     

Resonant third harmonic generation of a short pulse laser in plasma by applying a wiggler magnetic field

We examine the effect of wiggler magnetic field on pulse slippage of short pulse laser-induced third harmonic generation in plasma. The process of third harmonic generation of an intense short pulse laser in plasma is resonantly enhanced by the application of a magnetic wiggler. The laser exerts a ponderomotive force at second harmonic driving density oscillations. The second harmonic oscillations coupled with electron velocity at the laser frequency, produces a non-linear current, driving the third harmonic. Third harmonic pulse generates in the fundamental pulse domain. However, the group velocity of the third harmonic wave is greater than the fundamental wave. Hence, the third harmonic pulse saturates strongly and moves forward from the fundamental pulse at shorter distance than the second harmonic pulse.     

Mean force on a small sphere in a sound field in a viscous fluid

A mean force exerted on a small rigid sphere by a sound wave in a viscous fluid is calculated. The force is expressed as a sum of drag force coming from the external steady flow existing in the absence of the sphere and contributions that are cross products of velocity and velocity derivatives of the incident field. Because of the drag force and an acoustic streaming generated near the sphere, the mean force does not coincide with the acoustic radiation pressure, i.e., the mean momentum flux carried by the sound field through any surface enclosing the sphere. If the sphere radius R is considerably smaller than the viscous wave penetration depth delta, the drag force can give the leading-order contribution (in powers of delta/R) to the mean force and the latter can then be directed against the radiation pressure. In another limit, delta< or =R, the drag force and acoustic streaming play a minor role, and the mean force reduces to the radiation pressure, which can be expressed through source strengths of the scattered sound field. The effect of viscosity can then be significant only if the incident wave is locally plane traveling.