Plasma-maser interaction of langmuir wave with kinetic Alfvén wave turbulence

A theoretical study is made on the generation mechanism of Langmuir mode wave in the presence of kinetic Alfvén wave turbulence in a magnetized plasma on the basis of plasma-maser interaction. It is shown that a test high frequency Langmuir mode wave is unstable in the presence of low frequency kinetic Alfvén wave turbulence. The growth of the Langmuir wave occurs due to direct and polarization coupling terms. Because of the universal existence of the kinetic Alfvén waves in large scale plasmas, the results have potential importance in space and astrophysical radiation processes.     

Plasma-maser instability of the ion acoustics wave in the presence of lower hybrid wave turbulence in inhomogeneous plasma

A theoretical study is made on the generation mechanism of ion acoustics wave in the presence of lower hybrid wave turbulence field in inhomogeneous plasma on the basis of plasma-maser interaction. The lower hybrid wave turbulence field is taken as the low-frequency turbulence field. The growth rate of test high frequency ion acoustics wave is obtained with the involvement of spatial density gradient parameter. A comparative study of the role of density gradient for the generation of ion acoustics wave on the basis of plasma-maser effect is presented. It is found that the density gradient influences the growth rate of ion acoustics wave.     

The evolution of the resonant mode in plasma-maser interaction

We study the evolution of the resonant waves considering its interaction with the nonresonant waves and the plasma particles due to plasma-maser effect. The nonlinear dielectric function of the resonant wave is calculated and is found to consist of two parts: the direct and the polarization coupling terms. On the other hand, the nonlinear dielectric function of the nonresonant wave consists only of the direct coupling term. The significance of our results is discussed.     

Nonlinear evolution of a three-dimensional transverse wave packet in a hot plasma including the effect of its interaction with an ion-acoustic wave

By a perturbation method two coupled nonlinear partial differential equations are obtained for the nonlinear evolution of a three dimensional transverse wave packet in a hot plasma including the effect of its interaction with a long wavelength ion-acoustic wave. From these two equations a nonlinear dispersion relation is obtained, from which the instability condition of a uniform transverse wave train including the effect of its interaction, both at resonance and at nonresonance with a long wavelength ion-acoustic wave, are deduced. Resonance occurs when the component of group velocity of the longitudinal wave along the direction of propagation of the ion-acoustic wave is equal to the phase velocity of the wave. Assuming the usual type of dependence of amplitude on space and time the coupled equations are transformed into two other coupled equations, which reduced to a single nonliear Schrödingsr equation when three dimensionality is disregarded. It is found that these three transformed equations cannot give instability condition at resonance.On leave fromThe Department of Mathematics, University of Kalyani, West Bengal, India.     

Growth of a laser ripple in a magnetoplasma and its effect on plasma wave excitation

Summary This paper presents an investigation of the growth of a radially symmetrical ripple, superimposed on a Gaussian laser beam in a collisionless magnetoplasma. The effect of the magnetic field and the intensity of the laser on the growth of the ripple is presented in some detail. The effect of the presence of the ripple on the excitation of an electron plasma wave is also investigated. Coupling of a weak plasma wave with the main laser beam is through the modified background density. The combined effect of increased intensity of the laser beam and magnetic field is observed to suppress the growth of the ripple as well as the excitation of the plasma wave. The authors of this paper have agreed to not receive the proofs for correction.     

Resonant decay of a Langmuir wave in the presence of dust grains in a cylindrical plasma

The resonant parametric decay of a Langmuir wave into a backward propagating Langmuir wave and an ion acoustic (IA) wave is studied in a cylindrical dusty plasma. The analysis shows that the frequency of the IA mode decreases with the parameter δ_c (where δ_c is the ratio of the ion density to the electron density) for negatively charged dust grains. The growth rate of the resonance decay instability (RDI) and the threshold required for its onset also decrease with δ_c and are strongly dependent on the electron to ion temperature ratio for both positively and negatively charged dust grains. The results obtained also illustrate the dependence of the threshold of the resonance decay instability (μ_th) on the plasma cylinder radius.     

Acoustic backscattering enhancements resulting from the interaction of an obliquely incident plane wave with an infinite cylinder

Background and objective

The analysis of the acoustic backscattering enhancements from tilted cylinders is of particular importance in determining some of the (visco)elastic properties of the cylinder, and/or its surrounding fluid in ultrasonic non-destructive evaluation (NDE) and imaging (NDI) applications. Previous related investigations on an aluminum cylinder limited to incidence angles varying from 0° to 40°, revealed the existence of an anomalous “pseudo-Rayleigh” mode (above the critical Rayleigh angle) identified as the rigid-body translational dipole (n = 1) mode. The objective here is to provide a complete investigation on the backscattering enhancements for incidence angles larger than 40° for various elastic and viscoelastic cylinder materials.

Method

Using the partial-wave series solution for the linear scattering by an infinite circular cylinder, the acoustic backscattering from isotropic elastic and viscoelastic (polymer-type) cylinders excited by an obliquely incident plane acoustic wave is investigated. Total and resonance backscattering form functions are calculated for several elastic and viscoelastic cylinder materials immersed in water versus the angle of incidence 0° ? α < 90°. The “pure” resonance peaks are isolated by subtracting a rigid background from the total form function, so the associated resonance modes are properly identified.

Results and conclusion

The plots of the partial-wave series reveal acoustic backscattering enhancements (not shown in previous investigations) generally occurring at ka? 0.1 at a critical angle α_c bounded by the longitudinal and shear waves coupling angles θ_L=sin^-1(c/c_L) and θ_S=sin^-1(c/c_S) such that θ_L<α_c<θ_S (where c_L and c_S are the phase velocities of the longitudinal and shear waves inside the elastic cylinder, and c is the speed of sound in the surrounding medium). It is shown here that the backscattering enhancements with a critical angle θ_L<α_c<θ_S result from the excitation of the monopole (n = 0) resonance mode. Moreover, additional acoustic backscattering enhancements still occur in the range 1 ?ka? 6 even though the angle of tilt is greater than the Rayleigh wave coupling angle θ_R=sin^-1(c/c_R) (where c_R is the Rayleigh wave velocity in an elastic half-space). The resonance scattering theory shows that such additional enhancements are associated with the excitation of a dipole (n = 1) resonance mode which may result from the interference of meridional and/or helical waves propagating along the cylinder’s surface. It is therefore essential to consider tilt angles ranging from normal to end-on incidence for a complete analysis of the backscattering by elastic and viscoelastic cylinders.