Unmagnetized Plasma Research Articles

Method to penetrate through the overdense plasma sheath: Mode conversion in nonuniform plasmas with two-temperature electron population

Electromagnetic wave (EMW) penetration through an overdense plasma sheath is a critical subject in solving the “communication blackout” issue. Based on the numerical electron fluid numerical simulations, the linear mode conversion between EMW and electron acoustic waves (EAWs) was examined in the unmagnetized nonuniform plasma sheath with two-temperature electron population. The first resonant position of EMW in the plasma sheath is crucial to stimulate EAW efficiently, while the second one plays an important role in electromagnetic radiation from EAW. Owing to the mode conversion and EAW propagation, a channel can be opened in the overdense nonuniform plasma sheath for EMW. The transmission efficiency of EMW will be reduced remarkably for lacking a low density region where the mode conversion takes place.

Thermoacoustic instability in a two-dimensional dusty plasma: A study in the weakly and strongly coupled regime

Thermoacoustic instability in a two-dimensional unmagnetized dusty plasma has been investigated with the implementation of the general hydrodynamic model both in strongly and weakly coupled regimes. It has been found that the thermoacoustic modes are unstable in the long wavelength limit both in strongly and weakly coupled regimes although the modes literally die out in the weakly coupled regime due to viscous damping. The amplification of the thermoacoustic mode is triggered by the positive feedback response of the system via density and temperature fluctuations. The higher the thermal diffusivity, the higher the chances of mode stabilization.

Dust-acoustic envelope solitons in strongly coupled dusty plasmas

The propagation nature and the modulational instability (MI) criteria of low frequency amplitude modulated dust-acoustic envelope solitons are analyzed theoretically and numerically in an unmagnetized dusty plasma consisting of strongly coupled micron-sized inertial dust grains, Boltzmann distributed non-inertial electrons and ions. A hydrodynamical fluid model approach is used, based on [V. V. Yaroshenko, F. Verheest, H. M. Thomas and G.E. Morfill, New J. Phys. 11, 073013 (2009); V. V. Yaroshenko, V. Nosenko, and G. E. Morfill, Phys. Plasmas, 17, 103709 (2010)], where the strong coupling between dust grains for by an effective electrostatic pressure is accounted, which is in fact a dynamical function of the dust-density and the electrostatic potential. It is seen that the strong coupling between dust particles due to the effective electrostatic ``pressure” modifies the wavepacket stability and affects the occurrence of MI. A cubic nonlinear Schrodinger-type equation, which describes the evolution of the wavepacket’s envelope, is derived by adopting a multiscale technique for the amplitude dynamics. It is shown that long-wavelength dust-acoustic wavepackets are stable, while MI sets in beyond a carrier wavenumber threshold, which is evaluated in terms of intrinsic plasma parameters of relevance. On the other hand, the MI window is larger for higher ion density. The effect of the ion number density on MI is twofold, in that a higher ion density leads to a higher threshold (thus, the wave will be modulationally unstable for the larger values of the carrier wavenumber) but it also entails a wider instability window (hence, external perturbations must be of specific wavenumbers to trigger the instability). Numerical simulation confirms that the bright-type envelope soliton solution is stable beyond the carrier wavenumber threshold, i.e., in the modulationally unstable region, while the dark type envelope soliton is stable for wavenumbers below the threshold.

Electrostatic dust‐acoustic envelope solitons in an electron‐depleted plasma

AbstractA standard nonlinear Schrödinger equation has been established by using the reductive perturbation method to investigate the propagation of electrostatic dust‐acoustic waves, and their modulational instability as well as the formation of localized electrostatic envelope solitons in an electron‐depleted unmagnetized dusty plasma system comprising opposite polarity dust grains and super‐thermal positive ions. The relevant physical plasma parameters (viz., charge, mass, number density of positive and negative dust grains, and super‐thermality of the positive ions, etc.) have rigorous impact to recognize the stability conditions of dust‐acoustic waves. The present study is useful for understanding the mechanism of the formation of dust‐acoustic envelope solitons associated with dust‐acoustic waves in the laboratory and space environments.

Investigation of ion - acoustic wave dynamics in unmagnetized grain plasmas

In this work, we study an extended (3+1)-dimensional Jimbo-Miwa equation. We analyze the dynamics of three-dimensional nonlinear ion-acoustic waves in an unmagnetized plasma. We furnish the Lie symmetry technique to investigate the symmetry reductions of the examined model. The arbitrary functions involved in the Lie vectors are secured by using an optimization process, that leads to a reduction of the number of vectors in the commutator table. We next apply the singular manifold method (SMM) to the obtained reduced equations. This will result in a Schwarzian derivative whose solution will lead to new traveling wave solutions.

Modulation of the Nonlinear Ion Acoustic Waves in a Weakly Relativistic Warm Plasma with Nonextensively Distributed Electrons

A reductive perturbation technique (multiple scales) is applied to a weakly relativistic warm unmagnetized adiabatic plasma system consisting of inertial ions fluid and nonextensively distributed electrons. A nonlinear Schrodinger-type (NST) equation for finite wave number at the second order is derived. Using the reductive perturbation technique we derived the corresponding Korteweg-de Vries (K-dV) equation. For small wavenumber limit the K-dV equation is transformed into NST equation. It is found that the coefficient of the NST equation obtained from the K-dV equation agree with the corresponding coefficients of NST equation obtained by the multiple scales. Moreover we investigated the effect of the physical parameters of the system namely temperature ratio of the ion temperature T_i to electron temperature T_e, the relativistic factor u_0/C as well as the nonextensive parameter (q) of the distribution on the stability/instability of the system. It is found that these parameters affect strongly on the stability/instability regions. Finally, the validity of our results in astrophysical plasma is briefly discussed.

Self-focusing of high power beam in unmagnetized plasma and its effect on Stimulated Raman scattering process

In present study, Self-focusing of high power beam in unmagnetized plasma and its effect on Stimulated Raman scattering (SRS) process is investigated. Both relativistic-ponderomotive nonlinearities are taken together. Electron plasma wave (EPW) interacts nonlinearly with pump beam thereby leading to SRS. Under combined action of relativistic-ponderomotive forces, nonlinearity in plasma dielectric function is set up. This further causes change in plasma’s density profile in perpendicular direction to pump beam axis. This modification greatly influences input beam, scattered beam and EPW. Nonlinear differential equations for input beam, scattered beam and EPW are set up using Wentzel Kramers Brillouin approximation and paraxial theory. Numerical simulations are executed for analyzing effect of well-known parameters of laser and plasma medium on focusing/defocusing of various beams involved in the process and SRS back-reflectivity. It is confirmed that focusing of beams involved raises SRS back-reflectivity.

Overtaking Collisions of Ion Acoustic N-Shocks in a Collisionless Plasma with Pair-Ion and (α,q) Distribution Function for Electrons

In this work, the effects of plasma parameters on overtaking collisions of ion acoustic multi-shocks are studied in an unmagnetized collisionless plasma with positive and negative ions, and (α,q)-distributed electrons. To investigate such phenomena, the reductive perturbation technique is implemented to derive the Burgers equation. The N-shock wave solution is determined for this equation by directly implementing the exponential function. The result reveals that both the amplitudes and thicknesses of overtaking collisions of N-shock wave compressive and rarefactive electrostatic potential are significantly modified with the influences of viscosity coefficients of positive and negative ions. In addition, the density ratios also play an essential role to the formation of overtaking collisions of N-shocks. It is observed from all theoretical and parametric investigations that the outcomes may be very useful in understanding the dynamical behavior of overtaking collisions of multi-shocks in various environments, especially the D- and F-regions of the Earth’s ionosphere and the future experimental investigations in Q-machine laboratory plasmas.

Propagation of Electrostatic Solitary Waves in the Four-Component Dusty Plasma

We investigate the nonlinear dynamics of an unmagnetized dusty plasma comprising of four components, such as positively and negatively charged mobile dust, the Boltzmann distributed electrons, and nonthermal ions. The associated set of fluid equations is recasted into the celebrated nonlinear Schrodinger equation (NLSE) by invoking the standard reductive perturbation method. We have constructed a set of solitary antikink pulses by employing the exponential function method (EFM). It is found that the nonthermal ionic variable plays a key role in determining the electrostatic structure in the dusty plasma. The present investigation may have potential applications in predicting the nature of electrostatic solitary structures noticed in Saturn's ring.

Multi-component dense plasma with ion and super-thermal electrons with kappa distribution

The soliton waves are one of the nonlinear phenomena which can propagate in the different types of plasma such as multiple particles of plasma, nonthermal plasma, and space plasma. Using the Sagdeev potential technique, the stability conditions of the soliton waves in the nonthermal plasma have been theoretically studied. One of the significant factors that can affect the propagation of the soliton waves is the distribution function such as nonMaxwellian distribution function or Kappa distribution function. In this paper, we try to investigate the soliton wave in the unmagnetized multi-component plasma consisting of the nonthermal electron and the nonthermal ion, positron and dust with Kappa distribution function. Then by using the Sagdeev potential, the nonlinear equation for the potential is obtained and then the compression and rarefaction soliton waves are computed with the numerical method for this nonlinear wave. Finally, by imposing the Sagdeev potential condition, we discuss the stability of these soliton waves.

Investigation of Shock Waves in Nonextensive Electron–Positron–Ion Plasma with Relativistic Ions

Nonlinear propagation of ion-acoustic (IA) shock wave in a nonextensive and relativistic plasma is investigated by deriving space fractional Korteweg–de Vries–Burgers (SFKB) equation. This unmagnetized and collisionless plasma contains relativistic thermal ions, q-distributed electrons, and positrons. A modified tanh-function method is presented to solve the obtained SFKB equation taking space fractional and relativistic parameters, electrons nonextensivity, positrons nonextensivity, and electron-to-positron temperature ratio. It is observed that the structure of the IA shock wave can be modified by space fractional parameters. On the other hand, the IA shock wave shape can be modulated using the space fractional parameter. Our results can help understand the astrophysical environments such as pulsar magnetospheres, quasars, and collimated jets.

Inverse problem of the cylindrical Korteweg-de Vries equation for dust ion acoustic waves in unmagnetised plasma

Inverse problem of the cylindrical Korteweg-de Vries equation for dust ion acoustic waves in unmagnetised plasma

Temperature distributions and gradients in laser-heated plasmas relevant to magnetized liner inertial fusion.

We present two-dimensional temperature measurements of magnetized and unmagnetized plasma experiments performed at Z relevant to the preheat stage in magnetized liner inertial fusion. The deuterium gas fill was doped with a trace amount of argon for spectroscopy purposes, and time-integrated spatially resolved spectra and narrow-band images were collected in both experiments. The spectrum and image data were included in two separate multiobjective analysis methods to extract the electron temperature spatial distribution T_{e}(r,z). The results indicate that the magnetic field increases T_{e}, the axial extent of the laser heating, and the magnitude of the radial temperature gradients. Comparisons with simulations reveal that the simulations overpredict the extent of the laser heating and underpredict the temperature. Temperature gradient scale lengths extracted from the measurements also permit an assessment of the importance of nonlocal heat transport.

Propagation of the nonlinear damped Korteweg‐de Vries equation in an unmagnetized collisional dusty plasma via analytical mathematical methods

In this article, we consider the problem formulation of dust plasmas with positively charge, cold dust fluid with negatively charge, thermal electrons, ionized electrons, and immovable background neutral particles. We obtain the dust‐ion‐acoustic solitary waves (DIASWs) under nonmagnetized collision dusty plasma. By using the reductive perturbation technique, the nonlinear damped Korteweg‐de Vries (D‐KdV) equation is formulated. We found the solutions for nonlinear D‐KdV equation. The constructed solutions represent as bright solitons, dark solitons, kink wave and antikinks wave solitons, and periodic traveling waves. The physical interpretation of constructed solutions is represented by two‐ and three‐dimensional graphically models to understand the physical aspects of various behavior for DIASWs. These investigation prove that proposed techniques are more helpful, fruitful, powerful, and efficient to study analytically the other nonlinear nonlinear partial differential equations (PDEs) that arise in engineering, plasma physics, mathematical physics, and many other branches of applied sciences.

The generalized criterion for collisionless plasma sheaths with kappa distributed electrons

In this paper, by analytical estimation and numerical analysis of the ions Mach number domain in an unmagnetized collisionless plasma sheath, the formation condition of a stable sheath has been examined and formulated in the context of kappa distribution formalism. In this study, by theoretical investigation of the normalized variables with respect to well-defined parameters that enclose recent findings of kappa distribution formalism, a generalized Bohm criterion is derived in terms of an extended Mach number, , and a generalized polytropic index, γe, which characterizes different thermodynamic states with a general flexibility from near-thermal equilibrium states to the far-from-thermal equilibrium states. In our formulation, the allowed domains of isothermal and extended Mach number with respect to the connection between the polytropic index and the kappa distribution has been examined. By definition of the extended Mach number, the necessity of supersonic ions at the edge of sheath remains unchanged, but its appearance is different in the terms of the isothermal Mach number. It is shown that the threshold of extended Mach number in far-from-thermal equilibrium states is a sensitive function of the generalized polytropic index and it decreases by closing to the asymptotic limit of anti-equilibrium state (). Moreover, the threshold of isothermal Mach number decreases in the sub-isothermal regions with γe < 1 and so, by closing to the far-from-thermal equilibrium states, the Mach number domain is extended. Specially, it is shown that the thickness of the plasma sheaths reduces for the kappa distributed plasmas with smaller polytropic indices γe. Finally, the possibility for formation of stable plasma sheaths in different thermodynamic sates is discussed, where the validity of the generalized sheath criterion has been confirmed and given by or equivalently .

A Mathematical Modelling with Zakharov System for Langmuir Wave in Unmagnetized Plasma

A Mathematical Modelling with Zakharov System for Langmuir Wave in Unmagnetized Plasma

On the interaction of nonlinear ion acoustic solitary waves in non-ideal plasma incorporated with Cairns-Gurevich distributed electrons

A rigorous theoretical study of the head-on collision (HoC) of two ion acoustic solitons in unmagnetized non-ideal plasmas containing warm fluid ions and Cairns-Gurevich distributed electrons is presented. The extended Poincare-Lighthill-Kuo (PLK) method is employed and coupled modified Kortweg-de Vries (mKdV) equations describing the system are derived. The nonlinear evolution equations for the colliding solitons, the corresponding phase shifts and trajectories of the two solitary waves are calculated and analyzed numerically. It is found that the process of solitons collision strongly depends on the hybrid nonthermal trapped electron parameter. Shortly, it is detected that the collision phase shifts increase with the increment of the nonthermal parameter in the case of ideal plasma. Though, for ideal plasma case, the phase shifts are constant and larger than that of non-ideal case. The gained results could be useful in clarifying the requisite features of localized electrostatic disturbance in the Earth’s magnetosphere where such distribution exists.

Stimulated Brillouin Scattering of high power beam in unmagnetized plasma: Effect of relativistic and ponderomotive nonlinearities

In present communication, Stimulated Brillouin scattering (SBS) of high power beam in unmagnetized plasma is investigated. Relativistic and ponderomotive non-linearities are considered simultaneously. There is generation of scattered wave due to interaction of pump wave with ion-acoustic wave (IAW). Here, nonlinearity in dielectric function of plasma is set up under combined effects of variation in mass of electrons on account of high intense lasers as well as variation in plasma density of electrons as a result of ponderomotive force. As a result of this, there is variation in density profile of plasma in a direction transverse to pump beam axis. Incident wave, IAW and Scattered wave are greatly affected due to variation in plasma density. WKB and paraxial ray approximations are used to set up nonlinear differential equations linked with pump wave, IAW, scattered wave and expression for SBS back-reflectivity. Since, analytical solution is not possible for these equations. So, 4th order Runge-Kutta method is used to solve these equations numerically for studying the variation of beams widths of various waves and SBS back-reflectivity against normalized distance of propagation for established parameters of laser and plasma. Further, SBS back-reflectivity is found to get enhanced due to self-focusing.

Symmetric Airy electron plasma wave

A symmetric Airy electron plasma (SAiEP) wave, which is caused by launching four Airy beams symmetrically in the initial plane in an unmagnetized collisionless plasma, is analytically investigated in this paper. In addition to intensity distributions, evolutions, and the potential of the SAiEP wave with different parameters, the difference between the SAiEP wave and the Airy-like electron plasma wave is studied as well. The results show that the SAiEP wave with different distances between the main lobes in the initial plane behaves differently as the decay factor changes. When the decay factor increases, the frequency and the amplitude of the potential become smaller. Besides, the SAiEP wave has the autofocusing property, while the Airy-like electron plasma wave has the weak diffraction property.

Ion source terms effect on collisional plasma sheath characteristics with non-extensively distributed electrons

A one-dimensional fluid model of an unmagnetized collisional plasma sheath consisting of q-non-extensive electrons and singly charged positive ions with finite temperature is developed and presented. The ions are described by the fluid model, which is based on the continuity and momentum equations of ions, while the electrons are considered obeying non-extensive distribution according to the Tsallis statistics. In this work, different ion source terms are used in order to compare their contribution. The modified Bohm sheath criterion is determined for different source terms to specify the ion velocity at sheath entrance. The model equations are solved numerically in the plasma-wall transition region. The effect of ion source terms on the collisional electropositive plasma sheath characteristics such as ion and electron density, electric potential, ion velocity, sheath width and space charge is investigated. The influence of the ionization frequency parameter on the sheath behavior has also been studied. The results obtained show a strong impact of ion source terms on the plasma sheath structure. It is also shown that the ion source terms effect increases significantly when the ionization frequency parameter increases.