Influence of 30-MeV α-particle beams on wave propagation in the Belousov-Zhabotinsky reaction

The generation of leading centers in the Belousov-Zhabotinsky reaction under the action of collimated radiation with a high linear energy transfer has been investigated. To get insight into the mechanism of the effect of radiation on the Belousov-Zhabotinsky reaction, the radicalator model was modified to involve the interaction of the reactants with the ^•OH radical produced by water radiolysis.     

Electromagnetic-wave propagation in a bounded magnetoplasma

Summary Dispersion diagrams (ωvs. k) are obtained by numerical solution of the dispersion relation and determinantal equation for electromagnetic waves propagation along the lines of force in a bounded, cold, uniform magnetoplasma for frequencies in the vicinity of the electron cyclotron frequency. The results for slow waves (ω/k<c) are compared with those given by the electrostatic theory. By using a combined numerical and analytical analysis the electrostatic theory is obtained from the electromagnetic one. A solution of the electromagnetic dispersion relation with azimuthal-mode indexm<0 is found to correspond to the right circularly polarized mode of the infinite magnetoplasma. It is shown that there is no counterpart to this mode in the azimuthally symmetricm=0 solution.

---

Riassunto Diagrammi di dispersione (ωvs. k) sono ottenuti mediante la soluzione numerica della relazione di dispersione e l’equazione determinantale per onde elettromagnetiche che si propagano lungo le linee di forza in un magnetoplasma limitato, freddo e uniforme per frequenze nelle vicinanze della frequenza del ciclotrone dell’elettrone. I risultati per onde lente (ω/k<c) sono confrontati con quelli dati dalla teoria elettrostatica. Usando un’analisi combinata numerica ed analitica la teoria elettrostatica è ottenuta da quella elettromagnetica. Si trova che una soluzione della relazione di dispersione elettromagnetica con l’indice del modo azimutalem<0 corrisponde con il modo destro a polarizzazione circolare del magnetoplasma infinito. Si mostra che non c’è alcuna controparte a questo modo nella soluzione a simmetria azimutalem=0.

---

Резюме Получаются дисперсионные диаграммы (зависимость ω отk) путем численного решения дисперсионных соотношений и детерминантного уравнения для электромагнутных волн, распространяющихся вдоль силовой линии в ограниченной, холодной, однородной магнитоплазме для частот вблизи электронной циклотронной частоты. Результаты для медленных волн (ω/k<c) сравниваются с предсказаниями электростатической теории. Электростатическая теория получается из электромагнитной теории с помощью численного и аналитического анализа. Обнаружено, что решение электромагнитного дисперсионного соотношения с азимутальным индексомm<0, соответствует правой циркулярно поляризованной моде бесконечной магнитоплазмы. Показывается, что отсутствует соответствующая этой моде часть в азимутально симметричномm=0 решении.

     

Parametric generation of whistler waves due to the interaction of high-frequency wave beams with a magnetoplasma

The parametric generation of low-frequency whistler waves by a pump wave beam formed by high-frequency whistler waves with close frequencies is studied experimentally. The electromagnetic fields excited by the beats of two co- or counterpropagating high-frequency waves, or by an amplitude-modulated pump are studied. It is shown that the nonlinear currents at the beat (modulation) frequency are generated by a transverse ponderomotive force arising due to the finite width of the high-frequency beam. In this case, the nonlinear azimuthal drift currents enclose the pump beam and can radiate low-frequency whistler waves to the surrounding plasma.     

Ion wave instability in a collisional magnetoplasma

Temperature relaxation mechanism is found to have a destabilizing effect on ion waves propagating nearly across the magnetic field in the presence of streaming electrons.     

Drift wave turbulence in a dense semi-classical magnetoplasma

A semi-classical nonlinear collisional drift wave model for dense magnetized plasmas is developed and solved numerically. The effects of fluid electron density fluctuations associated with quantum statistical pressure and quantum Bohm force are included, and their influences on the collisional drift wave instability and the resulting fully developed nanoscale drift wave turbulence are discussed. It is found that the quantum effects increase the growth rate of the collisional drift wave instability, and introduce a finite de Broglie length screening on the drift wave turbulent density perturbations. The relevance to nanoscale turbulence in nonuniform dense magnetoplasmas is discussed.     

On Transverse Electric (TE) wave propagation in a warm moving magnetoplasma with sinusoidal electron-density distribution

It has been shown, using the first three moment equations in conjunction with Maxwell's equations, that the wave equation for the TE mode in a warm moving stratified magnetoplasma transforms, for an assumed sinusoidal distribution of the electron density, to the standard form of the Hill's differential equation.     

Laboratory modeling of the interaction of electron beams with a magnetoplasma

We present the results of laboratory experiments in which the mechanisms of interaction of electron beams with whistler waves in a magnetoplasma are studied. Different mechanisms of whistler generation during the injection of a modulated electron beam in the plasma are studied, and the mechanism of conversion of the beam kinetic energy to radiation is demonstrated. The processes of whistler wave generation by the modulated beam at the ˇ Cerenkov and Doppler resonances are analyzed in detail. The excitation of whistler waves by means of a nonresonant mechanism of the transition radiation is studied.     

Generation of millimeter wave Gaussian beams and their propagation in a dielectric waveguide

Linearly polarized fundamental mode Gaussian beams were generated and coupled to a hollow circular oversized dielectric waveguide by placing the waist of the beam at the guide entrance. The transmission properties of the waveguide were characterized as a function of frequency for a variety of coupling conditions. These conditions included changes in the input beam waist radius, angle of incidence, and displacement perpendicular and parallel to the guide axis. It has been found that: 1.) power transmission is maximized when the waist of the input beam is centered at the guide input, injected normally, and has a radius of 0.43 times the waveguide radius, 2.) power transmission decreases rapidly with increasing angle of incidence and the rate of that loss increases with frequency, 3.) the waveguide preserves the linear polarization of the input beam, 4.) power transmission in the fundamental waveguide mode is not greatly affected by moderate displacements in the input beam position, and 5.) upon exit from the waveguide the launched EH₁₁ mode propagates as a fundamental mode Gaussian beam in the quasi-far field. The results compare favorably to the transmission theory of Belland and Crenn and approximately to the near and far field mode pattern theory of Degnan.     

The propagation of wave beams in 2D cascade-induced lattices

A new method of 2D periodic lattices excitation in quadratically nonlinear media with cascade interaction is suggested. It is shown that in such structures the all-optical management of laser beams could be carried out. The possibility of switching waveguides and changing the final energy distribution among channels using the phenomenon of discrete diffraction is demonstrated.     

Free vibration analysis of planar curved beams by wave propagation

In this paper, a systematic approach for the free vibration analysis of a planar circular curved beam system is presented. The system considered includes multiple point discontinuities such as elastic supports, attached masses, and curvature changes. Neglecting transverse shear and rotary inertia, harmonic wave solutions are found for both extensional and inextensional curved beam models. Dispersion equations are obtained and cut-off frequencies are determined. Wave reflection and transmission matrices are formulated, accounting for general support conditions. These matrices are combined, with the aid of field transfer matrices, to provide a concise and efficient method for the free vibration problem of multi-span planar circular curved beams with general boundary conditions and supports. The solutions are exact since the effects of attenuating wave components are included in the formulation. Several examples are presented and compared with other methods.     

Damping rates of waves in a switched magnetoplasma medium:longitudinal propagation

The interaction of a circularly polarized electromagnetic wave with a switched-on magnetoplasma medium is considered. A static magnetic field in the direction of propagation is assumed to be present, resulting in longitudinal propagation. The incident wave splits into three waves whose frequencies are different from that of the incident wave. It is shown that these waves ultimately damp out if the plasma is even slightly lossy. The damping of the waves is interpreted in terms of their attenuation with distance and decay with time as they propagate in the lossy plasma. The attenuation-length and decay-time constants of the waves are obtained, and their dependence on the incident-wave frequency and the gyrofrequency is examined. Optimum parameters for an experiment to detect these waves are suggested     

Current driven ion wave instability in a weakly ionized collisional magnetoplasma

Ion waves propagating nearly across the magnetic field in a weakly ionized plasma with cross-field electron streaming are shown to be unstable due to dissipative effects.     

Influence of oceanic turbulence on propagation characteristics of Gaussian array beams

Based on the power spectrum of oceanic turbulence proposed by Nikishov, the influence of oceanic optical turbulence on propagation of Gaussian array beams is studied in detail by using five propagation characteristic parameters (i.e., mean-squared beam width, Rayleigh range, turbulence distance, power in the bucket and Strehl ratio). It is shown that the influence of oceanic optical turbulence on propagation of laser beams becomes stronger as τ (ratio of temperature to salinity contribution to the refractive index spectrum) and χ_T (rate of dissipation of mean-squared temperature) increase and ɛ (rate of dissipation of kinetic energy per unit mass of fluid) decreases, which is in agreement with the further analysis of oceanic turbulence shown in this paper. Furthermore, it is concluded that propagation of laser beams is more affected by oceanic optical turbulence in abyssal region than that in active region or oceanic surface.     

Influence of turbulence on the beam propagation factor of Gaussian Schell-model array beams

The analytical expression for the beam propagation factor (M²-factor) of Gaussian Schell-model (GSM) array beams propagating through atmospheric turbulence is derived. It is shown that the M²-factor of GSM array beams depends on the beam number, the relative beam separation distance, the beam coherence parameter, the type of beam superposition, and the strength of turbulence. The turbulence results in an increase of the M²-factor. However, for the superposition of the intensity the M²-factor is less sensitive to turbulence than that for the superposition of the cross-spectral density function. The M²-factor of GSM array beams is larger than that of the corresponding Gaussian array beams. However, the M²-factor of GSM array beams is less affected by turbulence than that of the corresponding Gaussian array beams. For the superposition of the cross-spectral density function a minimum of the M²-factor of GSM array beams may appear in turbulence, which is even smaller than that of the corresponding single GSM beams.     

Influence of atmospheric turbulence on the propagation of superimposed partially coherent Hermite-Gaussian beams

The influence of atmospheric turbulence on the propagation of superimposed partially coherent Hermite-Gaussian (H-G) beams is studied in detail. The closed-form propagation equation of superimposed partially coherent H-G beams through atmospheric turbulence is derived. It is shown that the turbulence accelerates the evolution of three stages which superimposed partially coherent H-G beams undergo. The turbulence results in a beam spreading and a decrease of the maximum intensity. However, the larger the beam number M, the beam order m, the separate distance x_d, and the smaller the beam correlation length σ₀ are, the less the power focusability of superimposed partially coherent H-G beams is affected by the turbulence. Specially, superimposed partially coherent H-G beams are less sensitive to turbulence than superimposed fully ones, and than partially coherent H-G beams if the beam power focusability and the maximum intensity are taken as beam criterions. However, the maximum intensity of superimposed partially coherent H-G beams is less sensitive or more sensitive to turbulence than that of superimposed Gaussian Schell-model (GSM) beams depending on σ₀.     

Ion-acoustic wave propagation in plasmas with ion beams having afinite cross section

The propagation of a low-density-modulated ion beam with finite cross section in a homogeneous plasma is considered. Analytical expressions describing a Cerenkov-like radiation pattern are obtained. An experimental setup is described that is suitable for investigating these phenomena. The results are in qualitative agreement with the analytical expressions