Low-frequency Electrostatic Waves Research Articles

Self-gravitation effect on the nonlinear dynamics of an electron–positron–ion magnetoplasma

A new set of nonlinear equations governing the dynamics of low-frequency electrostatic drift waves in a self-gravitating electron–positron–ion (e–p–i) magnetoplasma with equilibrium density, temperature, magnetic field and velocity gradients has been derived. It is shown that possible stationary solutions of the nonlinear equations can be represented in the form of dipolar and tripolar vortices of gravitational potential. The results of the present investigation are useful to understand the nonlinear dynamics of low-frequency gravitational-drift waves in laboratory and astrophysical e–p–i magnetoplasmas.

Rayleigh instability in non-uniform multi-ion species magnetoplasmas

We present the Rayleigh instability of low-frequency (in comparison with the ion-gyrofrequency) electrostatic waves in multi-ion species plasmas containing equilibrium density gradient and transverse ion-sheared flows caused by the dc electric field. For this purpose, multi-fluid equations are used to obtain the governing equations for two-dimensional convective cells and pseudo-three-dimensional drift waves in a non-uniform magnetoplasma. Standard procedures are then employed to study the Raleigh instability. Thresholds and growth rates are obtained. Applications to Hall thrusters are discussed.

Dust-lower-hybrid instability in the presence of dust charge fluctuations in a magnetized dusty plasma

The growth and damping of the low-frequency electrostatic dust-lower-hybrid (DLH) wave have been examined in the presence of dust charge fluctuations in a uniform magnetized dusty plasma. To obtain the dust charge fluctuation effects, the charging currents of electrons and ions to a spherical dust grain in a uniform magnetized dusty plasma have been calculated under the orbit-limited motion approximation. It is found that the external magnetic field reduces the charging currents, thereby reducing the dust charge fluctuation damping of a low-frequency electrostatic wave in a dusty plasma. However, for sufficiently low-frequency DLH wave having a finite parallel wave number, the thermal electrons may give rise to an instability of the DLH wave.

Ultra Low Frequency Electrostatic and Electromagnetic Waves in Electron-Positron Plasmas Induced by Rotation

It is shown that the rotation can induce ultra low frequency electrostatic and electromagnetic waves in electron-positron plasmas. In the nonlinear regime these waves can give rise to solitary structures in the form of vortices. The relevance of this investigation to astrophysical plasmas like pulsars is pointed out.

Electrostatic vortices associated with ion-temperature-gradient driven drift modes in electron-positron-ion plasmas

A set of nonlinear equations governing the dynamics of low-frequency electrostatic waves in the presence of equilibrium density, temperature, magnetic field and electrostatic potential gradients has been derived. In the linear limit, it is shown that nonzero equilibrium ion-temperature-gradient and the presence of positrons modify the basic drift modes. On the other hand, in the nonlinear case, it is shown that under certain conditions possible stationary solutions of the same set of nonlinear equations are reduced in the form of various types of vortex patterns. The results of the present investigation should be useful to understand the wave phenomena in laboratory and astrophysical e-p-i plasmas.

Microwave-generated low-frequency plasma wave excited in the periphery of the evanescent layer

The observation of microwave-created low-frequency electrostatic waves from the evanescent layer in a pulsed plasma discharge and effects of a weak magnetic field on its propagation characteristics are reported. The creation of the electrostatic wave depends on the density variations along the direction of microwave propagation. It is observable when a part of the microwave is reflected and another part of it eventually gets absorbed in the resonance-absorption layers (ɷ=ɷpe) on two sides of the evanescent layer. The velocity of the wave is one order of magnitude higher than that of the ion-acoustic wave. Under the application of a very weak magnetic field (affecting only the electrons) perpendicular to the direction of propagation of both the excited plasma waves and the microwaves, the waves are still observable only with altered velocity and characteristics. At higher magnetic fields the electrostatic waves are completely subdued under a continuous instability independent of presence or absence of the microwaves.

Sheared-flow-driven ion-acoustic drift-wave instability and the formation of quadrupolar vortices in a nonuniform electron–positron–ion magnetoplasma

A system of nonlinear equations which governs the dynamics of low-frequency (in comparison with the ion gyrofrequency) electrostatic waves in a nonuniform electron–positron–ion (e-p-i) magnetoplasma with sheared ion flows is presented. In the linear limit, a dispersion relation is obtained that admits new instabilities of drift-waves. It is found that ion-acoustic and electrostatic drift waves can become unstable due to ion sheared flow. Furthermore, the nonlinear interactions between these finite amplitude short-wavelength waves give rise to quadrupolar vortices. The relevance of the investigation to laboratory and astrophysical plasmas is pointed out.

Electrostatic instabilities and nonlinear structures of low-frequency waves in nonuniform electron–positron–ion plasmas with shear flow

It is found that the low-frequency ion acoustic and electrostatic drift waves can become unstable in uniform electron–ion and electron–positron–ion plasmas due to the ion shear flow. In a collisional plasma a drift-dissipative instability can also take place. In the presence of collisions the temporal behavior of nonlinear drift-dissipative mode can be represented in the form of well-known Lorenz and Stenflo type equations that admit chaotic trajectories. On the other hand, a quasi-stationary solution of the mode coupling equations can be represented in the form of monopolar vortex. The results of the present investigation can be helpful in understanding electrostatic turbulence and wave phenomena in laboratory and astrophysical plasmas.

Dust charge fluctuations in a magnetized dusty plasma.

Charging currents of electrons and ions to a spherical dust grain in a uniform magnetized dusty plasma have been examined. It is found that the external magnetic field reduces the charging currents, thereby decreasing the dust charge fluctuation damping of a low-frequency electrostatic wave in a dusty plasma.

Interaction of suprathermal solar wind electron fluxes with sheared whistler waves: fan instability

Abstract. Several in situ measurements performed in the solar wind evidenced that solar type III radio bursts were some-times associated with locally excited Langmuir waves, high-energy electron fluxes and low-frequency electrostatic and electromagnetic waves; moreover, in some cases, the simultaneous identification of energetic electron fluxes, Langmuir and whistler waves was performed. This paper shows how whistlers can be excited in the disturbed solar wind through the so-called "fan instability" by interacting with energetic electrons at the anomalous Doppler resonance. This instability process, which is driven by the anisotropy in the energetic electron velocity distribution along the ambient magnetic field, does not require any positive slope in the suprathermal electron tail and thus can account for physical situations where plateaued reduced electron velocity distributions were observed in solar wind plasmas in association with Langmuir and whistler waves. Owing to linear calculations of growth rates, we show that for disturbed solar wind conditions (that is, when suprathermal particle fluxes propagate along the ambient magnetic field), the fan instability can excite VLF waves (whistlers and lower hybrid waves) with characteristics close to those observed in space experiments.Key words. Space plasma physics (waves and instabilities) – Radio Science (waves in plasma) – Solar physics, astrophysics and astronomy (radio emissions)

Space-time evolution of electron-beam driven electron holes and their effects on the plasma

Abstract. We report here further results from the three-dimensional particle-in-cell simulations of the electron-beam driven electron holes. We focus here on (i) the transformation of oscillatory waves driven by the electron-beam instability into electron holes, (ii) the continued evolution and propagation of electron holes after their formation, including merging of electron holes, and (iii) the effects of the evolution on the plasma density and ion velocity distribution function. We find that initially electron-beam modes with perpendicular wave numbers k^ = 0 and as well as k^ ≠ 0 are driven resonantly below the electron plasma frequency of the target plasma. The modes interact nonlinearly and modulate each other both in space and time, producing wave structures with finite perpendicular scale lengths. Nonlinear evolution of such wave structures generates the electron holes in the simulations. Initially, a large number of electron holes form in the plasma. Their merging yields continuously a decreasing number of electron holes. The propagation velocity of the electron holes evolves dynamically and is affected by their merging. At late times only a few electron holes are left in the simulation and they decay by emitting low-frequency electrostatic whistler waves just above the lower hybrid (LH) frequency vlh . These waves, which are long structures parallel to the ambient magnetic field B0 and quite short transverse to B0, are associated with similar structures in the plasma density, producing density filaments. It turns out that electron-beam driven plasmas, in general, develop such filaments at some stage of the evolution of the beam-driven waves. In view of the excitation of the LH waves near vlh, which could resonate with the ions, an analysis shows that it is possible to heat transversely the ions in a time scale of a few seconds in the auroral return current plasma, in which electron holes and transversely heated ions have been simultaneously observed.

Some cross-field instabilities in magnetized dusty plasmas

It is shown that the resonant streaming energy associated with cross-field motions (due to the cross product of dc electric and magnetic fields) of the plasma particles can be coupled to low-frequency electrostatic waves. Conditions under which unstable waves appear are obtained for both collisionless and collisional dusty magnetoplasmas. The relevance of the present investigation to understanding the origin of nonthermal fluctuations in laboratory and space plasmas is pointed out.

Low frequency dusty plasma modes in a uniform magnetic field

Low frequency electrostatic waves of dusty plasmas in a uniform magnetic field are investigated. Since in conventional experiment parameter ranges the dust particles can hardly be magnetized, a “moderately magnetized” assumption of magnetized electrons and ions and unmagnetized dust particles is applied to such dusty plasmas. Effects of the neutral gas damping and the ion drag force on dust particles are taken into account. In the frequency range of ion waves, both dust-ion-acoustic waves propagating parallel to the magnetic field and the ion cyclotron waves are damped due to the ion drag on dust particles. In the very low dust frequency range, a new mode of slow dust waves propagating across the field line is found. The mode is damped to zero frequency in the long wavelength range due to the neutral gas damping and ion drag.

Low-frequency electrostatic waves in self-gravitating dusty plasmas with dust-ion collisions.

The influence of dust-ion collisions on low-frequency modes in a self-gravitating dusty plasma is studied. The stability of the system is easily determined using elementary principles of rootlocus theory. It shows that collisions between ions and dust grains do not change the criteria for gravitational collapse at any value of their collision frequency, but diminish the growth rate of unstable dusty plasmas. Moreover, the rootlocus plots visualize qualitatively the evolution of the real frequencies and damping decrements of the dust-acoustic and ion-acoustic modes as the dust-ion collision frequency increases.

Numerical simulations of a three-wave coupling occurring in the ionospheric plasma

Abstract. We studied a three-wave coupling process occurring in an active experiment of microwave power transmission (MPT) in the ionospheric plasma by performing one-dimensional electromagnetic PIC (Particle-In-Cell) simulations. In order to examine the spatial variation of the coupling process, we continuously emitted intense electromagnetic waves from an antenna located at a simulation boundary. In the three-wave coupling, a low-frequency electrostatic wave is excited as the result of a nonlinear interaction between the forward propagating pump wave and backscattered wave. In the simulations, low-frequency electrostatic bursts are discontinuously observed in space. The discontinuity of the electrostatic bursts is accounted for by the local electron heating due to the bursts and the associated modification of the wave dispersion relation. In a case where the pump wave propagates along the geomagnetic field Bext , several bursts of Langmuir waves are observed. Since the first burst consumes a part of the pump wave energy, the pump wave is weakened and cannot trigger the three-wave coupling beyond the region where the burst occurs. Since the dispersion relation of the Langmuir wave is variable, due to the local electron heating by the burst, the coupling condition eventually becomes unsatisfied and the first interaction becomes weak. Another burst of Langmuir waves is observed at a different region beyond the location of the first burst. In the case of perpendicular propagation, the upper hybrid wave, one of the mode branches of the electron cyclotron harmonic waves, is excited. Since the dispersion relation of the upper hybrid wave is less sensitive to the electron temperature, the coupling condition is not easily violated by the temperature increase. As a result, the three-wave coupling periodically takes place in time and eventually, the transmission ratio of the microwaves becomes approximately 20%, while almost no attenuation of the pump waves is observed after the first electrostatic burst in the parallel case. We also examined the dependency of the temporal growth rate for the electrostatic waves on the amplitude of the pump wave.

Low Frequency Nonlinear Waves in the Auroral Plasma

The nonlinear evolution of low frequency electrostatic waves in a magnetised plasma is investigated for parameters characteristic of the auroral acceleration region. Our model consists of Boltzmann electrons and warm ions. Using fluid theory, a nonlinear evolution equation is derived for the wave potential. Numerical solutions show the existence of sinusoidal, sawtooth or bipolar waveforms. The effects of plasma parameters on the wave amplitude are examined, in particular the effect of a finite ion temperature.

Addendum to “Charge Variation Effects on Low-Frequency Electrostatic Waves in Dusty Plasmas”

Addendum to “Charge Variation Effects on Low-Frequency Electrostatic Waves in Dusty Plasmas”

Comment on “Role of quasineutrality in drift waves” [Phys. Plasmas 8, 368 (2001)

The physics of various low-frequency electrostatic and electromagnetic waves in a nonuniform magnetoplasma is revisited. It is shown that the approach of Saleem and Haque [Phys. Plasmas 8, 368 (2001)] is misleading with regard to the electrostatic limit and the role of the quasineutrality approximation.

Coherent Structures of Dust-Drift Waves in a Dusty Plasma

A new type of very low-frequency electrostatic wave in a dusty plasma,called the dust-drift wave, has been investigated with the three-componentfluid model. The dispersion of the waves depends strongly on thedust grain content in plasma. Due to their nonlinear interaction, thedust-drift waves can form two-dimensional dip-hump and multi-peak localizedstructures. The amplitudes of those structures decrease with the increasingdust content.

Formation of a tripolar vortex in a contaminated electron-positron magnetoplasma with sheared flows

We derive a system of nonlinear equations governing the dynamics of low-frequency electrostatic waves in a magnetized pair plasma with sheared flows that is contaminated by dust grains. For some specific profiles of the equilibrium sheared flows, the nonlinear equations admit a stationary solution in the form of a tripolar vortex. The implications of our investigation to laboratory and space plasmas are discussed.