Rarefactive Solitons Research Articles

Ion-acoustic solitons in a relativistic Fermi plasma at finite temperature.

The theory of ion-acoustic solitons in nonrelativistic fully degenerate plasmas and nonrelativistic and ultra-relativistic degenerate plasmas at low temperatures is known. We consider a multi-component relativistic degenerate electron-positron-ion plasma at finite temperatures. Specifically, we focus on the intermediate region where the particle's thermal energy and the rest mass energy do not differ significantly, i.e., . However, the Fermi energy is larger than the thermal energy and the normalized chemical energy ( ) is positive and finite. Two different parameter regimes with and , relevant for astrophysical plasmas, are defined, and the existence of small amplitude ion-acoustic solitons in these regimes are studied, including the critical cases where the known KdV (Korteweg-de Vries) theory fails. We show that while the solitons with both the positive (compressive) and negative (rarefactive) potentials coexist in the case of , only compressive solitons can exist in the other regime . Furthermore, while the rarefactive solitons within the parameter domains of and can evolve with increasing amplitude and hence increasing energy, the energy of compressive solitons reaches a steady state.

Nonlinear dust ion acoustic solitary waves propagation in a magnetized plasma with Tsallis electron distribution

Abstract We have done a theoretical investigation into the propagation of nonlinear dust ion acoustic solitary waves and their soliton properties in a three-component magnetized collisionless plasma consisting of inertial positively charged ions, noninertial electrons following a Tsallis q–distribution, and stationary negatively charged dust grains. We consider a uniform external magnetic field along the z–direction, and the wave propagation occurs obliquely to the magnetic field direction. It is observed that the two types of wave modes namely slow and fast modes, are appears in the linear analysis. By employing the reductive perturbation method, the Korteweg-de Vries (KdV) and modified KdV equations are determined to describe the small amplitude dust ion acoustic soliton. The dependence of several physical plasma parameters including nonextensive q–parameter, magnetic field strength etc. of our plasma on the propagating dust ion acoustic solitary waves potential are numerically examined. This study shows the simultaneous existence of compressive and rarefactive solitons due to the variation of first order nonlinearity coefficient represented by the KdV equation and it is found that there is a critical point for the plasma parameters where the amplitude of the soliton of KdV equation become diverges. The mKdV equation with second order nonlinearity coefficient is derived from there and observed the solitons only with finite amplitude. The present study could be helpful for understanding the nonlinear travelling waves propagating in laboratory and space plasma environments.

Numerical validation of Yukawa fluid excitations within the quasilocalized charge approximation (QLCA) theory

AbstractA first principle molecular dynamics (MD) simulation study on the nonlinear excitations in a quasi‐localized state of a Yukawa system is presented to validate the findings of the nonlinear quasi‐localized charge approximation (QLCA) model. Unlike solids or gases, quasi‐localized states lack certain simplifying features, such as the ability to assume a fixed shape or volume, and they combine large displacements with strong interactions, further complicating the theoretical underpinnings of their behavior. In a recent paper [P. Kumar and D. Sharma, Physics of Plasmas 30 (2023)], the nonlinear QLCA model was applied to characterize the nonlinear excitations in a quasi‐localized state of a Yukawa system, as existing continuum models have shown limited success in this regime. The simulation data presented with the screening and coupling parameters show a close agreement with the QLCA model findings. The MD simulations validate the prediction made by the QLCA model that the properties of a soliton remain unaffected by variations in the coupling parameter. The prediction made by QLCA regarding the formation of multiple solitons at higher screening parameter values has also been confirmed by the MD simulation data. The possibility of the formation of rarefactive solitons at relatively high screening parameter values within the QLCA model is also discussed.

Small amplitude solitary electron acoustic wave for hot electrons taking regularized kappa distribution

AbstractThe properties of small‐amplitude solitary electron acoustic waves in a plasma where the hot electrons take regularized kappa distribution are investigated via the reductive perturbation method. It is found there only exists the sup‐electron‐acoustic rarefactive soliton, the electron acoustic velocity is modified by the regularized kappa distribution. The amplitude and width of the electron acoustic soliton decrease monotonously with the increase of the exponential cutoff parameter of hot electrons. But they vary with respect to the spectral index non‐monotonously. As to the observed parameters in the Earth's inner magnetosphere, the speed, electric field strength, and the width of solitary electron acoustic wave are comparable with the observations.

Coupled nonlinear drift and IAWs in streaming O–H plasma of upper ionosphere

Nonlinear structures formed by the coupled drift wave (DW) and ion acoustic waves (IAWs) are studied in a magnetized inhomogeneous collisionless bi-ion plasma with ions shear flow along the ambient magnetic field B=B0ẑ. The electrons are assumed to follow double spectral index (r, q) distribution in which r shows the flat top nature, while q is responsible for the shape of the distribution at the tail. A nonlinear differential equation is derived, and its solutions in the form of double layers (DLs) and solitons are obtained in different limits. It is pointed out that the presence of (0.4%) protons in the oxygen plasma of ionosphere should not be ignored because acoustic speeds corresponding to oxygen and hydrogen ions have small ratio of about four and drift wave frequency may lie in the same range. It is found that only the rarefactive solitons can be formed by the nonlinear DW and IAWs in the inhomogeneous oxygen hydrogen (O–H) plasma. However, the theoretical model predicts that both compressive and rarefactive DLs may be formed. The linear instabilities of low-frequency electrostatic waves due to field-aligned shear flow of ions have also been investigated.

Excitation of nonlinear longitudinal structures in spin‐1/2 quantum plasma in the presence of ion beam

AbstractThe formation of longitudinal, nonlinear structures in an interacting ion beam, spin‐1/2 quantum, electron‐ion plasma is reported by employing a separate spin evolution quantum hydrodynamic model (SSE‐QHD). The reductive perturbation method is followed to develop the KdV equations. In the presence of an ion beam and keeping the finite electron inertial effects, ion acoustic (IA) soliton and spin electron acoustic (SEA) soliton are found. The critical values of beam speed and spin polarization, required for the existence of solitary structures, are highlighted. It is prescribed that the present model supports rarefactive and compressive SEA soliton and compressive IA soliton. It is shown that the ion beam is essential for the existence of a compressive SEA solitary structure. We have also calculated and compared the energy densities of both solitons. Furthermore, the dependence of the nonlinear structures on the beam parameters and spin polarization are also examined. Our findings would be useful to understand the new spin‐dependent nonlinear structures as well as the features of nonlinear IA waves in ion beam–plasma interactions.

Effect of nonthermal electron distributions on dust acoustic solitons in cometary plasmas

We investigate the effect of nonthermal electrons modeled by two non-Maxwellian distribution functions, i.e., the (r, q) and Cairn’s distributions on the formation of dust acoustic (DA) solitons in an un-magnetized dusty plasma by incorporating the effect of dust streaming. We adopt the pseudopotential technique to obtain solitary wave solutions from fluid equations. It is seen that only rarefactive soliton can be obtained in such plasmas where ions are considered Boltzmannian and electrons non-Maxwellian. We find that soliton characteristics are strongly dependent on the nonthermal spectral indices r, q, and α and dust temperature Td. For (r, q) distribution, it is found that soliton amplitude increases but width decreases when the positive (negative) value of r decreases (increases). For Cairn’s distribution, we find that with the increase in α, soliton amplitude decreases. In space environments, such as cometary tails, solar wind, and Earth’s magnetosphere, where non-Maxwellian populations of electrons are present, our theoretical results show that the amplitude of soliton remains smaller than the Maxwellian case. Thus, Maxwellian distribution overestimates the soliton amplitude in such space environments. Therefore, we feel that our results will better interpret the results of observations, from cometary tails, and other space plasmas where nonlinear DA structures are likely to be observed.

Head on collision of multi ion acoustic solitons with arbitrary degenerate electrons

This study presents a head-on collision of ion-acoustic (IA) multiple solitons in unmagnetized quantum plasma with arbitrary degenerate electrons. The two-sided Korteweg–de Vries equations and phase shift associated with them have been derived using the extended Poincaré-Lighthill-Kuo (PLK) method. Depending on the quantum parameter’s value for the degenerate electrons, it is found that compressive and rarefactive solitons are formed. In addition, the Hirota bilinear approach is used to investigate the overtaking collision, and the expressions of phase shifts of multi-solitons interactions are determined. For a specific range of quantum diffraction, i.e, H < 2 compressional solitons propagating with supersonic speed, and for H > 2 the rarefactive solitons travelling with subsonic speed are found. A new nonlinear structure with a larger amplitude is produced during the collision in the interaction region. Graphically, the effects of different plasma parameters such as quantum diffraction and fugacity on interacting IA solitons structures and their associated phase shifts are investigated. The results of this study might help us to understand the collision of ion-acoustic solitons in an unmagnetized quantum plasma with arbitrary electrons degeneracy which can exist in astrophysical or laser plasma environment.

Existence of Korteweg-de Vries solitons and relevance of relativistic effects in a dusty electron-ion plasma

Nonlinear effects in the propagation of perturbations in a dusty electron-ion plasma are studied, considering fully relativistic wave motion. A multifluid model is considered for the particles, from which a KdV equation can be derived. In general, two different soliton solutions are found depending on the kind of dispersion of the KdV equation. We study when the dispersion coefficient of this equation is positive. In this case, two kinds of behavior are possible, one associated with a slow wave mode, another with a fast wave mode. It is shown that, depending on the value of the system parameters, compressive and/or rarefactive solitons, or no soliton at all, can be found and that relativistic effects for ions are much more relevant than for electrons. It is also found that relativistic effects can strongly decrease the soliton amplitude for the slow mode, whereas for the fast mode they can lead to compressive-rarefactive soliton transitions and vice versa, depending on the dust charge density in both modes.

Consequence of head-on collision of ion acoustic waves in unmagnetized plasmas having generalized (r, q) distributed electrons and positrons

To explore the effect of the head-on collision (such as phase shifts, collisional processes, and production of solitons) of ion-acoustic waves (IAWs), a collisionless unmagnetized electron-positron-ion (e-p-i) plasma is considered. The electrons and positrons follow the generalized () distribution. To do this, using the extended Poincaré-Lighthill-Kuo (ePLK) approach, the two-sided Korteweg-de Vries (KdV) equations and phase shifts are derived. The main aim of this study is to investigate the consequence of spectral indices and on both the negative and positive phase changes following an IAW-to-IAW collision. It is found that for the effects of the spectral indices of electrons and positrons both positive and negative phase shifts after head-on collisions are modified. The compressive (only hump-shaped) as well as rarefactive (both hump and dip-shaped) solitons become produced for the effect of spectral indices. The results obtained in the study may be helpful to understand the collision processes as well as the consequence of the head-on collision of IAWs in electron-positron-ion plasmas in the ionosphere, auroral acceleration regions, solar wind, Saturn rings, active galactic nuclei, polar cup of fast rotating neutron stars, semiconductor plasmas, and intense laser fields as well as in laboratory experiment.

Ion acoustic soliton with thermal ions and non-thermal electrons in a high-relativistic electron-positron-ion plasma

In this investigation, both compressive and rarefactive solitons are shown to exist in electron-positron-ion plasma consisting of thermal positrons, non-thermal electrons, and high relativistic thermal ions. The reductive perturbation method (RPM) is used to derive the nonlinear Korteweg-de Vries (KdV) equation from the governing normalized basic set of equations. It is shown that only the fast ion-acoustic mode may produce the small amplitude rarefactive and compressive KdV solitons. It has been observed that the addition of variable ion species temperature dramatically alters the fundamental characteristics of amplitude and width. Moreover, the amplitude decreases as the ion to electron temperature ratio rises. The soliton's amplitude is also increased by the relativistic factor. High-relativistic electron-positron-ion plasmas are found in extreme astrophysical environments like pulsar magnetospheres, gamma-ray bursts, and active galactic nuclei. These plasmas’ wave and soliton activity can shed light on the dynamics of these astrophysical systems.

Consequence of head‐on collision and double‐layer soliton with linear analysis in multi‐component dusty plasmas

AbstractThe unmagnetized multicomponent collisional dusty plasmas have been considered to investigate the consequence of head‐on collision of dust‐ion‐acoustic waves (DIAWs) with nonlinear characteristic analysis of DIAWs and collisionless plasmas have been considered for studying the production of double layer (DL). The plasma system consists of positively charged ion fluid, negatively charged cold dust fluid, thermal electrons, q‐nonextensive electrons, and immobile background neutral particles. The extended Poincaré‐Lighthill‐Kuo (ePLK) method has been used to derive two‐sided damped Korteweg–De Vries (dKdV) equations and the reductive perturbation method has been used to derive modified KdV (mKdV) equation and the standard Gardner equation (SGE). Linear dispersion relation is derived using linear perturbation technique. The nonlinear propagation of DIA Gardner solitons (DIAGSs) and double layers (DLs) as well as phase shifts have been investigated for the effects of the concerned parameters. It is found that the DIA soliton structures are significantly modified by the species densities, dust mass, and superextensive parameter. The rarefactive dip shape solitary Gardner solitons become produced for the effects of concerned parameters and the positive (negative) DLs become produced in the range of () for the effect of temperatures on the species. The superextensive and the subextensive parameters of electrons significantly affect the DL soliton structures.

Head-on collision of ion-acoustic (modified) Korteweg–de Vries solitons in Saturn's magnetosphere plasmas with two temperature superthermal electrons

In view of the recent observations by plasma science-spacecraft-voyager and Cassini plasma spectrometer of Saturn's magnetosphere, the interaction between two counter-propagating ion-acoustic (IA) solitons is studied in an unmagnetized plasma consisting of warm adiabatic ions in addition to hot and cold electrons following kappa distribution. The head-on collision of the IA solitons is investigated using the extended Poincare–Lighthill–Kuo technique. Since this model supports both compressive and rarefactive solitons, therefore, the soliton collisions for both Korteweg–de Vries (KdV) and the modified KdV (mKdV) equations are investigated. The corresponding phase shifts after the collision for both these equations are also derived and examined. Furthermore, the effects of different plasma parameters (corresponding to Saturn's magnetosphere), including superthermality, density, and temperature on the colliding soliton profiles and their phase shifts, are examined. It is concluded that the phase shift is smaller when both hot and cold electrons are Maxwellian by comparison with the superthermal case.

Electron beam driven ion-acoustic solitary waves in plasmas with two kappa-distributed electrons

Formation and the basic features of arbitrary amplitude ion-acoustic solitary waves (IASWs) in a plasma consisting of warm positive ions, two kappa-distributed electrons and an electron beam are investigated by using the Sagdeev pseudopotential approach. It is shown that the soliton existence domain (Mach number limits) sensitively depends on temperature of ions, spectral index of cool electrons and concentration of hot electron species while spectral index of hot electrons, hot-to-cool electron temperature ratio and also concentration of electron beam do not considerably affect this domain. It is also found that temperature of electron beam only affect the existence domain of rarefactive solitons. Furthermore, it is shown that considered plasma medium supports the coexistence of positive and negative IASWs. Moreover, effect of different plasma parameters such as hot-to-cool electron density ratio, ion-to-cool electron temperature ratio, beam-to-ion density ratio, hot-to-cool electron temperature ratio and superthermality index of electron species on the basic features of positive and negative IASWs is investigated numerically. Finally, the effect of plasma parameters on the parametric regime of coexistence of compressive and rarefactive IASWs is studied and, for example, effect of temperature of positive ions and number density of hot electrons on polarity of IASWs is numerically investigated.

On the propagation of cnoidal wave and overtaking collision of slow shear Alfvén solitons in low β magnetized plasmas

The overtaking collisional phenomenon of slow shear Alfvén solitons are studied in a low beta (β = kinetic pressure/magnetic pressure) collisionless, magnetized plasma consisting of electron and ion fluids. By employing a reductive perturbation technique, the Korteweg–de Vries (KdV) equation is deduced for investigating the nonlinear slow shear Alfvén wave. Before embarking on the study of the overtaking collisions, the stability analysis of the KdV equation is studied using the bifurcation theory. Also, a nonlinear periodic solution of the KdV equation is derived for the first time in the Weierstrass elliptic function formula. Moreover, the condition for converting the Weierstrass elliptic function expression to soliton is discussed. Furthermore, it is found that only density dip (rarefactive) solitons are formed in the super-Alfvénic regime. The next step includes the use of the Hirota bilinear method, which results in two and three shear Alfvén soliton solutions and their subsequent phase shifts. The influence of the plasma parameters on the amplitude as well as width of the slow shear Alfvén wave solitons are examined analytically and numerically. We also find out the profiles of overtaking interaction of slow shear Alfvén dip solitons having different amplitudes and speeds numerically. This study is important for understanding the phenomena of nonlinear slow shear Alfvén wave structures both in space and in laboratory plasmas.

Coexistence of positive and negative polarity solitons, double layers and supersolitons in electron-positron multi-ion plasmas

In order to analyze the nonlinear propagation of arbitrary amplitude ion-acoustic waves, the Sagdeev pseudopotential formalism is used to a four-component multi-ion plasma made up of inertial light positive ions, heavy negative ions, inertialess nonextensive electrons, and positrons. At first, we derived the expression of Sagdeev Pseudopotential for our plasma model and then numerically investigated the condition for the existence of several nonlinear structures such as solitons, double layers, supersolitons, etc. Based on numerical simulation, it is observed that within a certain range of parameters, our plasma model allows compressive as well as a rarefactive soliton, flat-top soliton, double layer, and supersoliton solutions. Great emphasis is placed on the determination of the existence regions for both solitons and supersolitons in the parameter space. Also, various nonlinear structures are explored to examine the effects of various plasma properties, such as the nonextensivity parameter, Mach number, etc. The findings of the current investigations may be helpful for comprehending significant features of ion-acoustic wave structures in space plasmas such as earth's ionosphere, cometary tails, etc., and laboratory plasmas like laser-plasma interaction research.

Study of compressive and rarefactive lump solitons structures in dusty plasma with double spectral (r,q) distributed electrons

Nonlinear features are revealed by one of the most competent and powerful approaches, i.e. soliton theory. The present article starts with the dust collisionless magnetized plasma where electrons are following double spectral ( r , q ) distribution. From the hydrodynamical governing equations set, Kadomtsev–Petviashvili (KP) equation is derived using the reductive perturbation technique. The derived KP equations are converted to standard KP equations by a suitable transformation to use the Hirota bilinear method (HBM) more conveniently. By using HBM, an auxiliary function is constructed, and through symbolic computation, three arbitrary constant sets are formed. These sets associate with three lump soliton solution sets. Finally, all these lump soliton solutions are returned back by the inverse transformation that was used to make the derived KP equation to the standard KP equation and get the lump soliton solution of the associated system. It is investigated that associated plasma parameters have a significant impact on the lump soliton structures while tracing figures using these plasma parameters within the justified range of the system. While lump soliton features' are analysed for various parameters' effect on it, one most important aspect is revealed. Double spectral index r and q play a significant role in the lump solitons structures and depict compressive and rarefactive lump soliton structures with the associated system. It is found that these double spectral indices r and q are the decision-making parameters for the lump soliton structures to be compressive or rarefactive.

Hirota bilinear method and multi-soliton interaction of electrostatic waves driven by cubic nonlinearity in pair-ion–electron plasmas

Multi-soliton interaction of nonlinear ion sound waves in a pair-ion–electron (PIE) plasma having non-Maxwellian electrons including Kappa, Cairns, and generalized two spectral index distribution functions is studied. To this end, a modified Korteweg–de Vries (mKdV) equation is obtained to investigate the ion-acoustic waves in a PIE plasma at a critical plasma composition. The effects of temperature and density ratios and the non-Maxwellian electron velocity distributions on the overtaking interaction of solitons are explored in detail. The results reveal that both hump (positive peak) and dip (negative peak) solitons can propagate for the physical model under consideration. Two and three-soliton interactions are presented, and the novel features of interacting compressive and rarefactive solitons are highlighted. The present investigation may be useful in laboratory plasmas where PIE plasmas have been reported.

Head-on collision between two-counter-propagating electron acoustic soliton and double layer in an unmagnetized plasma

The head-on collision between two-counter-propagating electron acoustic solitons and double layers (DLs) in an unmagnetized collisionless multi-species plasma consisting of inertial cold electron fluid and (α, q)-distributed hot electrons and positrons has been analyzed with the stationary background of massive positive ions. For nonlinear analysis of colliding wave phenomena, the coupled Korteweg–de Vries equation (KdVE), modified KdVE (mKdVE), and standard Gardner equation have been derived by adopting the extended Poincaré–Lighthill–Kuo technique. The effect of non-dimensional parameters on the collisional KdV, mKdV, and Gardner solitons (GSs) and DLs has been examined in detail by considering the limiting cases of (α, q)-distributions. It is found that the plasma model supports (i) the compressive and rarefactive collisional KdV solitons and GSs, (ii) only compressive mKdV solitons, and (iii) only rarefactive collisional DLs. The rarefactive collisional solitons are more affected by nonextensivity and the increase of the temperature of electrons than their compressive counterpart, whereas the rarefactive collisional DLs only existed in the presence of nonthermality.

Effect of dust charge polarization on the propagation characteristics of nonlinear Dust-acoustic solitons and double layers in superthermal un-magnetized complex plasma

The propagation characteristics of solitons and double layers associated with the dust-acoustic waves (DAWs) are studied in superthermal un-magnetized plasma through solitary and double layer solutions of the nonlinear Korteweg–de Vries (KdV) and the modified Korteweg–de Vries (mKdV) equations, respectively. The plasma constituents are superthermal electrons, superthermal ions, and dust particles. The electrons and ions follow the generalized Lorentzian velocity distribution while the dust particles are considered inertial and bear the charge polarization effect. In the small amplitude limit, we found that the phase velocity of the DAWs varies inversely with the polarization force. The effects of the polarization force and superthermality index on the properties of the solitons and double layer structures are also traced in the small but finite amplitude limit. It is found that the strong superthermality and dust charge polarization decrease the soliton’s energy. A study of the phase portrait is also carried out to investigate the propagation features of the solitary waves through parametric dependence of the configured plasma. It is found that for a selected set of configured parameters, the plasma system supports only rarefactive solitons. Furthermore, the amplitude of double layers has been observed to vary inversely with both the superthermality and the polarization force.