Experimental verification of the shear-modified ion-acoustic instability

The predicted shear-induced shift of the wave phase velocity, the essence of the shear-modified ion-acoustic (SMIA) instability mechanism that reduces ion Landau damping for otherwise damped ion-acoustic waves [V. Gavrishchaka et al., 80, 728 (1998)], is verified with direct measurements in a strongly magnetized laboratory plasma. The SMIA growth rate is shown to increase with increasing shear, as predicted. SMIA wave propagation is shown to be possible at both small and large angles to the magnetic field, consistent with space observations of ion-acoustic-like waves.     

Dust ion-acoustic wave oscillations in single-walled carbon nanotubes

In this paper, a charged single-walled carbon nanotube that surrounded by charged nanoparticles is modeled as a cylindrical shell of electron–ion–dust plasma. By employing the fluid theory for electron–ion–dust plasma, the dispersion relation of the dust ion-acoustic wave oscillations in the composed system is studied. For negatively charged dust particles, with increasing dust charge density, the phase velocity of the dust ion-acoustic wave will increase in comparison to the pure ion-acoustic wave oscillations.     

Mode transitions on the surface dust ion-acoustic wave in a semibounded dusty plasma

The effects of elongated rotating dust grains on the mode transitions of the dispersion relation of the surface dust ion-acoustic waves are investigated in a semi-bounded dusty plasma. The dispersion relation of the surface dust ion-acoustic wave is obtained by the plasma dielectric function with the specular reflection boundary condition. The result shows the existence of the dust ion-acoustic resonance modes in small and large wave number regions. It is also shown that the surface wave would be propagated in intermediate wave number domains. It is interesting to note that the wave propagation domain has been diminished with an increase of the rotation frequency.     

Nonlinear excitation and stability analysis of ion-acoustic waves in a magnetized quantum plasma with exchange-correlation effects of degenerate electrons

The nonlinear ion-acoustic wave excitation and its stability analysis are investigated in a magnetized quantum plasma with exchange-correlation and Bohm diffraction effects of degenerate electrons in the model. Using reductive perturbation technique, the Zakharov-Kuznetsov (ZK) equation is derived for two dimensional propagation of ion-acoustic wave in a magnetized quantum plasma. It is found that the phase speed, amplitude and width of the nonlinear ion-acoustic wave structures are affected in the presence of exchange-correlation potential in the model. The stability analysis of the 2D ion-acoustic wave pulse is also presented. It is found that growth rate of the first and second order instabilities of 2D ion acoustic wave soliton is enhanced with the inclusion of exchange-correlation potential effect in the model.     

A study of electron beams extracted from a plasma produced by laser interaction with a solid target

In this work, wave formation in laser-produced plasma is investigated by an analysis of time-of-flight signal of the electron pulse. Electrons are extracted from a non-equilibrium plasma, generated by pulsed laser ablation on a solid Ge target. The process is represented by ion-acoustic waves, which are generated from an external perturbation, given by the positive bias voltage of a Faraday cup. The characteristics of the waves depend substantially on the geometry of the plasma expansion chamber and on laser fluence, but are independent on bias potential. A KrF excimer UV laser was employed for plasma generation. Measurements were performed at two different laser fluences, 4 and 7 J/cm². The plasma created propagates with a mean velocity of about 1.1?×?10⁴ m/s. A movable Faraday cup was employed in order to collect electrons at different bias voltage values.     

Head-on collision of ion-acoustic solitary waves in an unmagnetized electron-positron-ion plasma

The head-on collision between two ion-acoustic solitary waves in an unmagnetized electron-positron-ion plasma has been investigated. By using the extended Poincaré-Lighthill-Kuo perturbation method, we obtain the KdV equation and the analytical phase shift after the head-on collision of two solitary waves in this three-component plasma. The effects of the ratio of electron temperature to positron temperature, and the ratio of the number density of positrons to that of electrons on the phase shift are studied. It is found that these parameters can significantly influence the phase shifts of the solitons. Moreover, the compressive solitary wave can propagate in this system.     

Oblique Interaction of Ion-Acoustic Solitary Waves in e-p-i Plasmas

In this study, we investigate the oblique collision of two ion-acoustic waves (IAWs) in a three-species plasma composed of electrons, positrons, and ions. We use the extended Poincare-Lighthill-Kuo (PLK) method to derive the two-sided Korteweg-de-Vries (KdV) equations and Hirota’s method for soliton solutions. The effects of the ratio (δ) of electron temperature to positron temperature and the ratio (p) of the number density of positrons to that of electrons on the phase shift are studied. It is observed that the phase shift is significantly influenced by the parameters mentioned above. It is also observed that for some time interval during oblique collision, one practically motionless composite structure is formed, i.e., when two ion-acoustic waves with the same amplitude interact obliquely, a new non-linear wave is formed during their collision, which means that ahead of the colliding ion-acoustic solitary waves, both the amplitude and width are greater that those of the colliding solitary waves. As a result, the nonlinear wave formed after collision is a new one and is delayed. The oblique collision of solitary waves in a two-dimensional geometry is more realistic in high-energy astrophysical pair plasmas such as the magnetosphere of neutron stars and black holes.     

Kinetic theory of surface waves in a semibounded plasma flow

A study is made of the spectrum of surface waves in a semibounded plasma flow. The frequency spectra and damping rates of the waves propagating along the flow are analyzed both in the high-frequency range (in which the spatial dispersion is weak and the wave damping is governed primarily by electron collisions) and the low-frequency range (in which the spatial-dispersion effects dominate), with focus on the effect of the flow velocity on the propagation of ion-acoustic waves. Special attention is paid to the penetration of a static field into a plasma flowing at a supersonic velocity.     

Modulational instability of ion—acoustic waves in a warm plasma

Using the standard reductive perturbation technique,a nonlinear Schroedinger equation is derived to study the modulational instability of finite-amplitude ion-acoustic waves in a non-magnetized warm plasma.It is found that the inclusion of ion temperature in the equation modifies the nature of the ion-acoustic wave stability and the soliton stuctures.The effects of ion plasma temperature on the modulational stability and ion-acoustic wave properties are inestigated in detail.     

Longitudinal electro-kinetic waves in ion-implanted semiconductor plasmas

A comprehensive investigation of propagation of new longitudinal electro-kinetic modes and novel properties introduced due to presence of negatively charged colloids in semiconductor plasma is presented. By employing the multi-fluid balance equations, a compact dispersion relation for the cases in which wave phase velocity is either larger or smaller than electron thermal velocity is derived. This dispersion relation is used to study wave phenomena and electro-kinetic mode instability numerically. We find important modifications in electro-kinetic branch as well as the existence of new modes of propagation in colloids laden semiconductor plasma. The results of this investigation should be useful in understanding the characteristics of longitudinal electro-kinetic wave in colloids laden semiconductor plasmas whose main constituents are electrons, holes and negatively charged colloids.Received: 15 June 2004, Published online: 7 September 2004PACS: 52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves) - 72.30. + q High-frequency effects; plasma effects - 61.72.Ww Doping and impurity implantation in other materials - 82.70.Dd Colloids     

Unstable mode of ion-acoustic waves with two temperature q-nonextensive distributed electrons

The linear characteristics of the unstable mode of ion-acoustic waves are examined in an electrostatic electron-ion plasma composed of streaming hot electrons, non-streaming cold electrons and dynamical positive ions. The plasma under consideration is modeled by using a non-gyrotropic nonextensive q-distribution function in which the free energy source for wave excitation is provided by the relative directed motion of streaming hot electrons with respect to the other plasma species. In the frame work of kinetic model, a linearized set of Vlasov–Poisson's equations are solved to obtain the analytical expressions for dispersion relation and Landau damping rate. The threshold condition for the unstable ionacoustic wave is derived to assess the stability of the wave in the presence of nonextensive effects. Growth in the wave spectrum and nontrivial effects of q-nonextensive parameter on the ion-acoustic waves can be of interest for the readers in the regions of Saturns' s magnetosphere.     

A Model for Periodic Nonlinear Electric Field Structures in Space Plasmas

In this study, we present a physical model to explain the generation mechanism of nonlinear periodic waves with a large amplitude electric field structures propagating obliquely and exactly parallel to the magnetic field. The ``Sagdeev potential' fromthe MHD equations is derived and the nonlinear electric field waveforms are obtained when the Mach number, direction of propagation, and the initial electric field satisfy certain plasma conditions. For the parallel propagation, the amplitude of theelectric field waves with ion-acoustic mode increases with the increase of initial electric field and Mach number but its frequency decreases with the increase of Mach number. The amplitude and frequency of the electric field waves with ion-cyclotron mode decrease with the increase of Mach number and become less spiky, andits amplitude increases with the increase of initial electric field. For the oblique propagation, only periodic electric field wave with an ion-cyclotron mode obtained, its amplitude and frequency increase with the increase of Mach number and become spiky. From our model the electric field structures show periodic, spiky, and saw-tooth behaviours corresponding to different plasma conditions.     

Effects of suprathermal particles on the dust ion-acoustic waves in a complex plasma

Dust ion-acoustic waves propagating in a complex plasma containing dusty particles and suprathermal electrons and ions are kinetically analyzed. The suprathermal particles are effectively modeled by the Lorentzian (kappa) velocity distribution function. For a collisionless and unmagnetized plasma, the full spectrum of the dispersion relation is obtained and the suprathermal particle effects on the wave frequency and the Landau damping are investigated. For a given wave number, the wave frequency decreases as the spectral index κ decreases, especially very rapidly in the low κ region. The Landau damping of the wave and its maximum are derived. They are found to be enhanced by the increase of suprathermal particles. The ion-to-electron density ratio also enhances the damping rate greatly.     

Supernonlinear ion-acoustic waves in a dusty plasma

An exact solution is obtained for the equations that describe nonlinear ion-acoustic waves in a dusty plasma. It is shown that the solution can be in the form of nonlinear periodic waves, solitons, and supernonlinear waves whose trajectories envelope one or several separatrices in the phase portrait of the wave. Profiles of physical quantities in the wave are constructed. The supernonlinear waves are shown to be of two types, subsonic (type 1) and supersonic (type 2). Existence regions of supernonlinear waves of both types and solitons are constructed in the plane of the problem parameters.     

Expansion,compression and triangular shockwaves in traffic flow above critical point

We study the formation of shockwaves from an initial condition of the pulse form in supercritical flow of traffic by using the optimal velocity model. The jam with the pulse form propagates with changing the initial form. The wave velocity is derived numerically and analytically. The dependence of wave velocity on headway is clarified. When the headway is lower than the safety distance, the rear of initial pulse evolves to the expansion shockwave, while the front of initial pulse evolves to the compression shockwave if the headway is higher than the safety distance. The dependence of wave velocity on headway determines whether either expansion or compression waves evolve to the shockwave. After the rear of initial pulse collapses with the front, the wave evolves to the triangular shockwave. It is shown that the triangular shockwave is described by the Burgers equation.     

Can ion-acoustic waves in plasma be backward waves?

The dispersion relation for ion-acoustic waves in plasma with ion flow has been analyzed. It is shown that these waves may exist (under certain conditions) in the form of backward waves with antiparallel group and phase velocities. The range of ion flow velocities allowing implementation of backward ion-acoustic waves is found.     

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.     

Nonlinear adiabatic models of ion-acoustic waves in dust plasma

Nonlinear adiabatic models of ion-acoustic waves in a dust plasma are developed. The problem of the structure of subsonic periodic and supersonic solitary ion-acoustic waves is exactly solved analytically under the assumption of a constant charge of dust particles; the critical Mach numbers for the solitary wave are determined. The problem of the wave structure is solved numerically for the case when the charge of dust particles was assumed to be variable.     

Korteweg-De Vries Equation for Non-Linear Ion-Acoustic Waves in a Plasma with Negative Ions

The theoretical analysis, based on the perturbation technique, of ion-acoustic waves in the vicinity of a Korteweg-de Vries (K-dV) equation derived in a plasma with some negative ions has been made. The investigation shows that the negative ions in plasma with isothermal electrons introduced a critical concentration at which the ion-acoustic wave plays an important role of wave-breaking and forming a precursor while the plasma with non-isothermal electrons has no such singular behaviour of the wave. These two distinct features of ion waves lead to an overall different approach of present study of ion-waves. A distinct feature of non-uniform transition from the nonisothermal case to isothermal case has been shown. Few particular plasma models have been chosen to show the characteristics behaviour of the ion-waves existing in different cases.