Excitation Of Ion-acoustic Waves Research Articles

Excitation of ion acoustic waves by Laguerre−Gaussian laser beams in collisionless plasma: combined effects of self focusing and density ramp

Excitation of ion acoustic waves by Laguerre−Gaussian laser beams in collisionless plasma: combined effects of self focusing and density ramp

Excitation of ion acoustic waves by self-focused q-Gaussian laser beam in plasma with axial density ramp

Excitation of ion acoustic waves by self-focused q-Gaussian laser beam in plasma with axial density ramp

A Study on Second Harmonic Excitation in Electron Beam–Plasma Instability

The electron beam–plasma interaction is a fundamental nonlinear plasma process that is frequently taking place in space and laboratory plasmas. Such an interaction is found to generate electromagnetic waves observed in space plasmas. Using the two-dimensional electromagnetic particle in cell simulations, we investigated the second harmonic excitation in the electron beam–plasma instability. Results showed that, first, the Langmuir waves are excited in the system; then at longer time scales, following the excitation of ion acoustic waves, the second harmonic electromagnetic waves are excited. We found that in the case of background pair plasmas, where the masses are the same, there is no signature of waves in the second harmonic, which is a direct verification of the three-wave coupling mechanism for the generation of electromagnetic waves in the second harmonic.

Triggered Ion-acoustic Waves in the Solar Wind

Abstract For more than 12 hr beginning on 2021 January 18, continuous narrowband electrostatic emissions were observed on the Parker Solar Probe near 20 solar radii. The observed <1000 Hz frequencies were well below the local ion-plasma frequency. Surprisingly, the emissions consisted of electrostatic wave packets with shock-like envelopes, appearing repetitively at a ∼1.5 Hz rate. This repetitiveness correlated and was in phase with low-frequency electromagnetic fluctuations. The emissions were associated with simultaneously observed ion beams and conditions favorable for ion-acoustic wave excitation, i.e., Te/Ti ∼ 5. Based on this information and on their velocity estimates of about 100 km s−1, these electrostatic emissions are interpreted as ion-acoustic waves. Their observation demonstrates a new regime of instability and evolution of oblique ion-acoustic waves that have not been reported previously in theory or experiment.

The Effect of Ion-to-Electron Mass Ratio on the Electron Beam-Plasma Interaction

Two-dimensional electromagnetic particle-in-cell simulations are carried out to investigate the effect of ion-to-electron mass ratio on the evolution of warm electron beam-plasma instability. Four cases are considered: A: mi/me = 0 (two-electron stream instability); B: mi/me = 1 (pair plasma); C: mi/me = 100; and D: mi/me = 1000. It is shown that the generation of Langmuir waves in the fundamental mode of electron plasma frequency and the subsequent dynamics of large-amplitude solitons are not affected by the ion species. However, it determines the decay process of solitons and the excitation of electromagnetic waves in the second harmonic. In the first two cases, mi/me = 0 and 1, there is no sign of emission in the second harmonic, while the strongest emission in the second harmonic is found for the case of largest mass ratio, mi/me = 1000. This confirms the two-step wave-wave coupling mechanism for the generation of second harmonic electromagnetic waves, which requires the excitation of ion-acoustic waves in the first step. Moreover, the dispersion diagrams of all excited waves are presented.

Theoretical models for unstable IAWs and nonlinear structures in the upper ionosphere

Physical mechanisms are discussed for the excitation of ion-acoustic waves (IAWs) by field-aligned shear flow of ions and parallel current produced by electrons in the upper ionospheric oxygen hydrogen plasma within auroral latitudes. Theoretical models are presented for the formation of solitary structures by nonlinear IAWs. It is pointed out that the small concentration of hydrogen ions in the oxygen plasma should not be ignored, because it plays important role in the linear instability of IAWs and in determining the size of the nonlinear electrostatic structures. The growth rates of IAWs and size of nonlinear structures vary with altitude, because both depend upon the density ratio of oxygen-to-hydrogen ions along with other parameters. Current-driven electrostatic ion-acoustic waves are studied using kinetic theory which shows that parallel current produces these waves if the concentration of protons is very small about 4% or lesser in the presence of field-aligned shear flow of both kind of ions. Fluid theory is used to look for shear flow-driven instabilities and formation of nonlinear structures ignoring ion temperature effects in this plasma where Freja observations indicate $$T_{i}\approx $$ (0.3–0.1) $$T_{e}$$ . Effects of nonthermal electrons and density gradient on the instabilities and size of the structures are also pointed out.

Self-focusing of cosh-Gaussian laser beam and its effect on the excitation of ion-acoustic wave and stimulated Brillouin backscattering in collisionless plasma

An analytical and numerical study has been carried out for self-focusing of an intense cosh-Gaussian laser beam in collisionless plasma and its impact on the excitation of ion-acoustic wave and stimulated Brillouin backscattering process. The analytical model has been developed under Wentzel–Kramers–Brillouin and paraxial ray approximations. The nonlinearities of ponderomotive force on electron and the relativistic oscillation of the electron mass have been used in this study. The nonlinear differential equations have been set up for the beam width parameters of the main beam, ion-acoustic wave, backscattered wave and back reflectivity of stimulated Brillouin scattering (SBS). These equations have been solved numerically for different values of decentred parameter (b), relative plasma density (ωp0/ω0) and incident laser intensity (a). The results have been compared with only relativistic nonlinearity and Gaussian profile of laser beam. The focusing of laser beam, ion-acoustic wave and scattered wave are found to be strong under relativistic-ponderomotive regime compared to only relativistic regime. Further, it is observed that focusing/intensity of main laser beam, ion acoustic wave and SBS back reflectivity increases with increasing the values of b and ωp0/ω0. Itis also found that back reflectivity of SBS process gets suppressed with the increase in the value of a. This study may be useful in laser induced fusion scheme where back scattering of SBS plays very important role.

Excitation of IAWs by ions shear flow and electron parallel current in positive-negative ion plasma

It is pointed out that the criterion ωpe≪ωp+, ωp− (where ωpj is the plasma oscillation frequency of jth species and j = e, +, −) presented to define pure pair-ion plasma must also be fulfilled to ignore electron dynamics in positive-negative ion plasma. It is also suggested that the potassium (K+) plasma having negative ions of perfluoromethylcyclohexane (C7F14−) produced in Q-machine seems to have a significant number density of electrons; therefore, ion acoustic waves (IAW) may also exist. If T±<Te and ions have field-aligned shear flow, the fluid theory predicts that the IAWs will be excited. The dimensions of experimentally produced plasma are small; therefore, the local theory is applicable only approximately. Since observations show that Te≃T± in the laboratory performed experiments with positive-negative ions, the kinetic theory is also used to look for electron current-driven IAWs. Kinetic theory predicts that IAWs will be highly damped if electrons flow antiparallel to B0 in opposite direction with respect to positive ions. On the other hand, if electrons flow along B0 as is the case of ionospheric plasma, then IAWs become unstable. Thus, field-aligned shear flow of ions and parallel electron current can produce IAWs both in laboratory and astrophysical electron positive negative ion plasmas.

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.

Electrostatic wave instability and soliton formation with non-thermal electrons in O-H plasma of ionosphere

It is pointed out that the presence of non-thermal electrons and protons in oxygen plasma of the ionosphere plays a destructive role in the formation of electrostatic structures by nonlinear ion acoustic waves (IAWs). On the other hand, linear electrostatic perturbations at different IAW frequencies are excited by the field-aligned shear flow in oxygen-hydrogen plasma of the upper ionosphere, and non-thermal electrons cause an increase in the growth rate. The excitation of IAW and formation of solitary structures in the ionosphere are investigated at altitudes of 600 km and 1000 km in the auroral region.

Extreme driven ion acoustic waves

The excitation of large amplitude, strongly nonlinear ion acoustic waves from trivial equilibrium by a chirped frequency drive is discussed. Under certain conditions, after passage through the linear resonance in this system, the nonlinearity and the variation of parameters work in tandem to preserve the phase-locking with the driving wave via excursion of the excited ion acoustic wave in its parameter space, yielding controlled growth of the wave amplitude. We study these autoresonant waves via a fully nonlinear warm fluid model and predict the formation of sharply peaked (extreme) ion acoustic excitations with local ion density significantly exceeding the unperturbed plasma density. The driven wave amplitude is bound by the kinetic wave-breaking, as the local maximum fluid velocity of the wave approaches the phase velocity of the drive. The Vlasov-Poisson simulations are used to confirm the results of the fluid model, and Whitham's averaged variational principle is applied for analyzing the evolution of autoresonant ion acoustic waves.

Excitation of ion-acoustic waves in the high-latitude ionosphere

The broadband electrostatic turbulence generally observed in the high-latitude ionosphere is a superposition of nonlocal waves of ion-acoustic and ion-cyclotron types. In the presence of a shear of ion parallel velocity, ion-acoustic modes can be induced by an instability emerging due to an inhomogeneous distribution of energy density. This paper is devoted to the studies of excitation of oblique ion-acoustic wave in background configurations with inhomogeneous profiles of both electric field and ion parallel velocity. A numerical algorithm has been developed, and instability was simulated at various parameters of background plasma. The general possibility of oblique ion-acoustic wave generation by a gradient of ion parallel velocity is shown. In this case, the wave spectrum is found to be broadband, which agrees with satellite observations.

Effects of ion motion on linear Landau damping

The effects of ion motion on Landau damping has been studied by the use of one-dimensional Vlasov-Poisson simulation. It is shown that the ion motion may significantly change the development of the linear Landau damping. When the ion mass is multiple of proton mass, its motion will halt the linear Landau damping at some time due to the excitation of ion acoustic waves. The latter will dominate the system evolution at the later stage and hold a considerable fraction of the total energy in the system. With very small ion mass, such as in electron-positron plasma, the ion motion can suppress the linear Landau damping very quickly. When the initial field amplitude is relatively high such as with the density perturbation amplitude δn/n0 > 0.1, the effect of ion motion on Landau damping is found to be weak or even ignorable.

Stimulated Brillouin backscattering of hollow Gaussian laser beam in collisionless plasma under relativistic–ponderomotive regime

AbstractStimulated Brillouin backscattering of an intense hollow Gaussian laser beam (HGLB) from collisionless plasma has been investigated under relativistic–ponderomotive regime. The main feature of considered hollow Gaussian laser beam is having the same power at different beam orders with null intensity at the center. Backscattered radiation is generated due to nonlinear interaction between main beam (pump beam) with pre-excited ion acoustic wave (IAW). Modified coupled equations has been set up for the beam width parameters of the main beam, ion-acoustic wave, back-scattered wave, and back reflectivity of stimulated Brillouin scattering (SBS) with the help of the Wentzel–Kramers–Brillouin approximation, fluid equations and paraxial theory approach. These coupled equations are solved analytically and numerically to study the laser intensity in the plasma, the variation of amplitude of the excited IAW and back reflectivity of SBS. The back reflectivity of SBS is found to be highly sensitive to the order of the HGLB, intensity of main laser beam, and plasma density for typical laser and plasma parameters. The focusing of main laser beam (hollow Gaussian) and IAW significantly affected the back reflectivity of SBS. The results show that the self-focusing and back reflectivity is enhanced for higher order modes of HGLB.

Influences of shear in the ion parallel drift velocity and of inhomogeneous perpendicular electric field on generation of oblique ion acoustic waves

AbstractIt is well known that the broadband electrostatic turbulence observed in the topside auroral ionosphere can be identified with electrostatic ion cyclotron and/or oblique ion acoustic waves. Under certain conditions generation of the ion cyclotron modes is inhibited, so that the oblique ion acoustic waves become the prevailing part of the broadband noise. While generation of ion cyclotron waves by the inhomogeneous distribution of energy density (IEDD) instability has been actively studied in recent years, much less attention was paid to the excitation of ion acoustic waves by means of the IEDD instability. In this work, influence of shear in the ion parallel drift velocities and of inhomogeneous perpendicular electric field on generation of nonlocal oblique ion acoustic mode is studied. It is demonstrated that the shear of the ion parallel drift velocities can generate ion acoustic waves. It is shown that this mechanism of instability development provides broadband spectrum in the frequency range around 0.1 of ion gyrofrequency, and thus, this instability can be invoked to explain the observed broadband electrostatic turbulence in the auroral region. Effect of the main background plasma parameters on excitation of oblique ion acoustic waves is analyzed.

Stimulated Brillouin backscattering of a ring-rippled laser beam in collisionless plasma

AbstractThe effect of the propagation of a ring-rippled laser beam in the presence of relativistic and ponderomotive non-linearities on the excitation of ion-acoustic wave (IAW) and resulting stimulated Brillouin backscattering in collisionless plasma at relativistic powers is studied. To understand the nature of propagation of the ring ripple-like instability, a paraxial-ray approach has been invoked in which all the relevant parameters correspond to a narrow range around the irradiance maximum of the ring ripple. Modified coupled equations for growth of ring ripple in the plasma, generations of IAW and back-stimulated Brillouin scattering (SBS) are derived from fluid equations. These coupled equations are solved analytically and numerically to study the intensity of ring-rippled laser beam and excited IAW as well as back reflectivity of SBS in the plasma for various established laser and plasma parameters. It is found that the back reflectivity of SBS is enhanced due to the strong coupling between ring-rippled laser beam and the excited IAW. The results also show that the back reflectivity of SBS reduce for higher intensity of the laser beam.

Effect of self-focused rippled laser beam on the excitation of ion acoustic wave in relativistic ponderomotive regime

AbstractThis paper presents an investigation of self-focusing of intense Gaussian rippled laser beam in collisionless plasma by including the nonlinearity associated with the relativistic mass and the ponderomotive force and its effects on the excitation of ion acoustic wave. The growth of ripple, riding on an intense Gaussian laser beam in plasma and its coupling with ion acoustic wave has also been studied. Modified coupled equations for main laser beam, growth of laser ripple in plasma, rippled laser beam, beam width, and density perturbation associated with ion acoustic wave are derived using Wentzel-Kramers-Brillouin and paraxial ray approximation. These coupled equations are solved analytically and numerically to study the laser intensity in plasma and the variation of amplitude of the ion acoustic wave for various established laser and plasma parameters. From numerical computation, it is observed that both nonlinearities significantly affected the dynamics of the growth of laser ripple in plasma, propagation of rippled laser beam as well as ion acoustic wave in plasma at high laser power flux. The growth of laser ripple increase with increase in the intensity of laser beam and due to the contribution of growth rate, intensity profile of rippled laser beam and ion acoustic wave modified accordingly.

ION DYNAMICS DURING THE PARAMETRIC INSTABILITIES OF A LEFT-HAND POLARIZED ALFVÉN WAVE IN A PROTON-ELECTRON-ALPHA PLASMA

The parametric instabilities of an Alfv´ en wave in a proton-electron plasma system are found to have great influence on proton dynamics, where part of the protons can be accelerated through the Landau resonance with the excited ion acoustic waves, and a beam component along the background magnetic field is formed. In this paper, with a one- dimensional hybrid simulation model, we investigate the evolution of the parametric instabilities of a monochromatic left-hand polarized Alfvwave in a proton-electron-alpha plasma with a low beta. When the drift velocity between the protons and alpha particles is sufficiently large, the wave numbers of the backward daughter Alfvwaves can be cascaded toward higher values due to the modulational instability during the nonlinear evolution of the parametric instabilities, and the alpha particles are resonantly heated in both the parallel and perpendicular direction by the backward waves. On the other hand, when the drift velocity of alpha particles is small, the alpha particles are heated in the linear growth stage of the parametric instabilities due to the Landau resonance with the excited ion acoustic waves. Therefore, the heating occurs only in the parallel direction, and there is no obvious heating in the perpendicular direction. The relevance of our results to the preferential heating of heavy ions observed in the solar wind within 0.3 AU is also discussed in this paper.

Stimulated Brillouin backscattering of filamented hollow Gaussian beams

AbstractThis paper presents an investigation for excitation of ion acoustic wave and resulting stimulated Brillouin scattering in a collisionless plasma due to presence of a laser beam carrying null intensity at center (hollow Gaussian beam). In presence of ponderomotive nonlinearity, the pump beam get focused and affects the back stimulated Brillouin scattering process. To understand the nature of laser plasma coupling, a paraxial-ray approximation has been invoked for the propagation of the hollow Gaussian beam, ion acoustic wave, and stimulated Brillouin scattering. It is observed from the result that self-focusing and back reflectivity reduces for higher order of hollow Gaussian beam.

Collective modes in sculpted ultracold neutral plasmas

We have pushed the study of collective modes into the Ultracold Neutral Plasma (UCNP) regime by sculpting the initial density distribution through spatial modulation of the ionizing laser. With this technique, we have excited ion acoustic waves (IAW) and measured dispersion in the long wavelength limit [1]. Additionally, we have produced streaming plasmas and observed the evolution of a possible instability. A high resolution 1:1 optical relay allows ionization modulation on length scales of ~ 100 μm, comparable to the Debye shielding length, which will access linear and nonlinear phenomenon for which strong coupling is predicted to modify the properties of collective modes.