Ion-acoustic solitons in pair-ion plasma with non-thermal electrons

Properties of fully nonlinear ion-acoustic solitary waves in an unmagnetized and collisionless pair-ion (PI) plasma containing superthermal electrons obeying Cairns distribution have been analyzed. A linear biquadratic dispersion relation has been derived, which yields the fast (supersonic) and slow (subsonic) modes in a pair-ion-electron plasma with nonthermal electrons. For nonlinear analysis, Korteweg-de Vries equation is obtained using the reductive perturbation technique. It is found that in case of slow mode, both electrostatic hump and dip type structures are formed depending on the temperature difference between positively and negatively charged ions, whereas, only dip type solitary structures have been observed for fast mode. The present work may be employed to explore and to understand the formation of solitary structures in the space (especially, the Earth’s ionosphere where two distinct pair ion species (H ^±) are present) and laboratory produced pair-ion plasmas with nonthermal electrons.     

Low frequency collective modes in dense relativistic-degenerate strongly coupled plasma

It is shown that low frequency electrostatic ion mode couples with electromagnetic shear Alfven mode in a dense plasma containing strongly coupled non-degenerate ion and relativistic degenerate electron fluids. By employing the appropriate fluid equations, a linear dispersion equation is obtained which shows modifications due to ion correlations and electron relativistic degeneracy. The results are discussed in the ultra-relativistic and weak-relativistic limits and implications of the results in dense degenerate plasmas of astrophysical origin (e.g., white dwarf stars) are pointed out with possible consequences.     

Kadomtsev–Petviashvili equation for solitary waves in warm dense astrophysical electron-positron-ion plasmas

Theoretical investigation is carried out to understand the dynamics and stability of three dimensional ion solitary waves propagating in dense plasma comprising of ultra-relativistic degenerate electrons and positrons and warm ions. A linear dispersion relation is derived which shows a strong dependence of wave on positron concentration (through the change of density balance) and ion-to-degenerate electron temperature ratio. A nonlinear Kadomtsev-Petviashvili equation is derived by employing the reductive perturbation technique and solved analytically and the conditions for existence of stable solitary waves are found. The analysis reveals that only compressive solitary waves exist in the system. Effects of the change of density balance and Fermi temperature ratios are studied in detail, both analytically and numerically. Furthermore, the conditions for stable solitary waves are discussed by using energy consideration method. The numerical results are also presented by using the parameters consistent with the degenerate and ultrarelativistic astrophysical plasmas.     

Kinetic theory of acoustic-like modes in nonextensive pair plasmas

The low-frequency acoustic-like modes in a pair plasma (electron-positron or pair-ion) is studied by employing a kinetic theory model based on the Vlasov and Poisson’s equations with emphasizing the Tsallis’s nonextensive statistics. The possibility of the acoustic-like modes and their properties in both fully symmetric and temperature-asymmetric cases are examined by studying the dispersion relation, Landau damping and instability of modes. The resultant dispersion relation in this study is compatible with the acoustic branch of the experimental data (Oohara et al. in Phys. Rev. Lett. 95:175003, 2005) in which the electrostatic waves have been examined in a pure pair-ion plasma. Particularly, our study reveals that the occurrence of growing or damped acoustic-like modes depends strongly on the nonextensivity of the system as a measure for describing the long-range Coulombic interactions and correlations in the plasma. The mechanism that leads to the unstable modes lies in the heart of the nonextensive formalism yet, the mechanism of damping is the same developed by Landau. Furthermore, the solutions of acoustic-like waves in an equilibrium Maxwellian pair plasma are recovered in the extensive limit (q→1), where the acoustic modes have only the Landau damping and no growth.     

Higher-order corrections to ion acoustic waves in degenerate electron-positron-ion plasmas

The nonlinear propagation of ion acoustic waves in ideal plasmas consisting of degenerate electrons and positrons, and isothermal ions is investigated. The Korteweg de Vries (K-dV) equation that contains the lowest order nonlinearity and dispersion is derived from the lowest order of perturbation and a linear inhomogeneous (K-dV type) equation that accounts for the higher order nonlinearity and the dispersion relation is obtained. The stationary wave solution for these equations has been found using the renormalization method. Also, the effects of electrons and positrons densities and ion temperature on the amplitude and width of solitary waves are investigated, numerically. It is seen that higher order corrections significantly change the properties of the K-dV solitons. Also, it is found that both compressive and rarefactive solitary waves can be propagated in such plasma system.     

Roles of positively charged heavy ions and degenerate plasma pressure on cylindrical and spherical ion acoustic solitary waves

The properties of heavy-ion-acoustic (HIA) solitary structures associated with the nonlinear propagation of cylindrical and spherical electrostatic perturbations in an unmagnetized, collisionless dense plasma system has been investigated theoretically. Our considered model contains degenerate electron and inertial light ion fluids, and positively charged static heavy ions, which is valid for both of the non-relativistic and ultra-relativistic limits. The Korteweg-de Vries (K-dV) and modified K-dV (mK-dV) equations have been derived by employing the reductive perturbation method, and numerically examined in order. It has been found that the effect of degenerate pressure and number density of electron and inertial light ion fluids, and positively charged static heavy ions significantly modify the basic features of HIA solitary waves. It is also noted that the inertial light ion fluid is the source of dispersion for HIA waves and is responsible for the formation of solitary waves. The basic features and the underlying physics of HIA solitary waves, which are relevant to some astrophysical compact objects, are briefly discussed.     

Arbitrary Amplitude Ion Acoustic Solitary Waves in An Unmagnetized Two Electron Population Ultra-Relativistic Dense Plasmas

The nonlinear wave structure of arbitrary amplitude ion acoustic solitary waves (IASWs) are studied in the Sagdeev’s pseudopotential framework for an ultra-relativistic degenerate dense plasma comprising cold and hot electrons and inertial ultra-cold ions. By employing standard normal-mode analysis the dispersion relation for linear waves is studied. The numerical results are presented to understand the features of ion acoustic solitary wave structures. It is shown that the present plasma model supports IASWs having positive potential well. Also, it is found that the small amplitude rarefactive double layer solution can exist in such a plasma system in some parametric region. It is shown that solitary structures and double layers are affected by relevant plasma parameters.     

Low frequency shear electromagnetic modes in strongly coupled, relativistic-degenerate, astrophysical electron-positron-ion plasmas

Starting from appropriate fluid equations, a dispersion relation describing the properties of low frequency (as compared to the ion gyrofrequency) shear electromagnetic mode in an ultra-dense, relativistic-degenerate plasma is derived and examined. The plasma constituents are fully degenerate electrons and positrons, and strongly correlated non-degenerate ions. It is found that the shear mode can couple with the electrostatic ion mode under certain circumstances. The electron and positron relativistic degeneracy and ion correlations significantly affect the waves. However, the electron degeneracy pressure is dominant because the density balance changes due to the presence of ions in electron-positron pair plasma. The results are discussed numerically in the ultra-relativistic and weakly-relativistic limits, indicating relevance to the dense plasmas, produced in laboratory (e.g., super-intense laser-dense matter experiments), and astrophysical regimes.     

Fully nonlinear heavy ion-acoustic solitary waves in astrophysical degenerate relativistic quantum plasmas

Fully nonlinear features of heavy ion-acoustic solitary waves (HIASWs) have been investigated in an astrophysical degenerate relativistic quantum plasma (ADRQP) containing relativistically degenerate electrons and non-relativistically degenerate light ion species, and non-degenerate heavy ion species. The pseudo-energy balance equation is derived from the fluid dynamical equations by adopting the well-known Sagdeev-potential approach, and the properties of arbitrary amplitude HIASWs are examined. The small amplitude limit for the propagation of HIASWs is also recovered. The basic features (width, amplitude, polarity, critical Mach number, speed, etc.) of HIASWs are found to be significantly modified by the relativistic effect of the electron species, and also by the variation of the number density of electron, light ion, and heavy ion species. The basic properties of HIASWs, that may propagated in some realistic astrophysical plasma systems (e.g., in white dwarfs), are briefly discussed.     

Ion acoustic solitary waves in plasma with nonthermal electron,positron and warm ion

In this paper, the characteristics of ion acoustic solitary waves are studied in plasmas containing warm ion fluid, non-thermally distributed electron and positron. We study the effects of non-thermal electrons and ion temperature on solitons by Pseudo-potential method and show that the parametric region where ion acoustic solitons can exist is modified. We also obtain linear dispersion relation by using the standard normal-modes analysis.     

Stability of ion-acoustic waves in a pair-ion plasma with a third species of ions: application to cometary plasmas

A popular model of a cometary plasma is hydrogen (H⁺) with positively charged oxygen (O⁺) as a heavier ion component. However, the discovery of negatively charged oxygen (O^?) ions enables one to model a cometary plasma as a pair-ion plasma (of O⁺ and O^?) with hydrogen as a third ion constituent. We have, therefore, studied the stability of the ion-acoustic wave in such a pair-ion plasma with hydrogen and electrons streaming with velocities $V_{d\mathrm{H}^{+}}$ and V _de , respectively, relative to the oxygen ions. We find the calculated frequency of the ion-acoustic wave with this model to be in good agreement with the observed frequencies. The ion-acoustic wave can also be driven unstable by the streaming velocity of the hydrogen ions. The growth rate increases with increasing hydrogen density $n_{\mathrm{H}^{+}}$ , and streaming velocities $V_{d\mathrm{H}^{+}}$ and V _de . It, however, decreases with increasing oxygen ion densities $n_{\mathrm{O}^{+}}$ and $n_{\mathrm{O}^{-}}$ .     

Noncommutative dispersion relation and mass-radius relation of white dwarfs

The equation of state of the electron degenerate gas in a white dwarf is usually treated by employing the ideal dispersion relation.However, the effect of quantum gravity is expected to be inevitably present and when this effect is considered through a non-commutative formulation, the dispersion relation undergoes a substantial modification.In this paper, we take such a modified dispersion relation and find the corresponding equation of state for the degenerate electron gas in white dwarfs.Hence we solve the equation of hydrostatic equilibrium and find that this leads to the possibility of the existence of excessively high values of masses exceeding the Chandrasekhar limit, although the quantum gravity effect is taken to be very small.It is only when we impose the additional effect of neutronization that we obtain white dwarfs with masses close to the Chandrasekhar limit with nonzero radii at the neutronization threshold.We demonstrate these results by giving numerical estimates for the masses and radii of helium, carbon and oxygen white dwarfs.     

Effect of quantum corrections on the Jeans instability of self-gravitating viscoelastic dusty fluid

In this paper we investigate the effects of quantum correction on the Jeans instability of self-gravitating viscoelastic dusty electron-ion quantum fluids. The massive self-gravitating dust grains are assumed to be strongly coupled and non-degenerate having both viscous and elastic behavior while the inertialess electrons and ions are considered as weakly coupled and Fermi degenerate. The hydrodynamic model is modified and a linear dispersion relation is derived employing the plane wave solutions on the linearized perturbation equations for the considered system. It is observed that the dispersion properties are affected due to the presence of viscoelastic effects and quantum statistical corrections. The modified condition of Jeans instability and expression of critical Jeans wavenumber are obtained. Numerically it is shown that viscoelastic effects, dust plasma frequency and quantum statistical effects all have stabilizing influence on the growth rate of gravitationally Jeans mode. The growth rates are also compared in kinetic and hydrodynamic limits and it is found that decay in the growth of unstable Jeans mode is larger under the kinetic limits than the hydrodynamic limits. The results are discussed for the understanding of formation of dense degenerate dwarf star through gravitational collapsing which is assumed to be strongly coupled dusty quantum fluid where the strongly coupled dust provides inertia and Fermi degenerate electron and ions provide quantum statistical effects.     

Effect of general loss-cone distribution function on electrostatic ion-cyclotron instability in an inhomogeneous plasma: particle aspect analysis

The electrostatic ion-cyclotron instability (EICI) in low β (ratio of plasma to magnetic pressure), anisotropic, inhomogeneous plasma is studied by investigating the trajectories of the particles using the general loss-cone distribution function (Dory-Guest-Harris type) for the plasma ions. In particular, the role of the loss-cone feature as determined by the loss-cone indices, in driving the drift-cyclotron loss-cone (DCLC) instability is analysed. It is found that for both long and short wavelength DCLC mode the loss-cone indices and the perpendicular thermal velocity affect the dispersion equation and the growth rate of the wave by virtue of their occurrence in the temperature anisotropy. The dispersion relation for the DCLC mode derived here using the particle aspect analysis approach and the general loss-cone distribution function considers the ion diamagnetic drift and also includes the effects of the parallel propagation and the ion temperature anisotropy. It is also found that the diamagnetic drift velocity due to the density gradient of the plasma ions in the presence of the general loss-cone distribution acts as a source of free energy for the wave and leads to the generation of the DCLC instability with enhanced growth rate. The particle aspect analysis approach used to study the EICI in inhomogeneous plasma gives a fairly good explanation for the particle energisation, wave emission by the wave–particle interaction and the results obtained using this particle aspect analysis approach are in agreement with the previous theoretical findings using the kinetic approach.     

Polarization of AGN in UV spectral range

We employ the Sagdeev pseudo-potential method to investigate the propagation of nonlinear ion waves in a relativistically degenerate electron-ion plasmas. The matching criteria for existence of such nonlinear excitations are numerically investigated in terms of the relativity measure (relativistic degeneracy parameter) of electrons and the allowed Mach-number range for propagation of such waves is evaluated. It is shown that the electron relativistic degeneracy parameter has significant effects on nonlinear wave dynamics in superdense degenerate plasmas such as that encountered in white dwarfs and the cores of massive planets.     

Dust-acoustic solitary and rogue waves in a Thomas-Fermi degenerate dusty plasma

The formation and propagation of dust-acoustic (DA) solitary and rogue waves are studied in a non-relativistic degenerate Thomas-Fermi thermal dusty plasma incorporating transverse velocity perturbation effects. The electrons and ions are described by the Thomas-Fermi density distributions, whereas the dust grains are taken as dynamic and classical. By using the reductive perturbation technique, the cylindrical Kadomtsev-Petviashvili (CKP) equation is derived, which is then transformed into a Korteweg-deVries (KdV) equation by using appropriate variable transformations. The latter admits a solitary wave solution. However, when the carrier waves frequency is much smaller than the dust plasma frequency, the DA waves evolve into the nonlinear modulation instability, generating modulated wave packets in the form of Rogue waves. For the study of DA-rogue waves, the KdV equation is transformed into a self-focusing nonlinear Schrödinger equation. The variation of dust temperature and the electron density affects the nonlinearity and dispersion coefficients which suppress the amplitudes of the DA solitary and rogue waves. The present results aim to describe the nonlinear electrostatic excitations in astrophysical degenerate dense plasma.     

Propagation of whistler mode ion-cyclotron wave through multicomponent plasma

The dispersion relation of an ion cyclotron wave propagating through a multicomponent plasma including the effect of ion thermal velocity is analysed and an analytical expression for the group travel time, and the temporal and spatial damping rate is derived. It is shown that the temporal and spatial damping rate increases with temperature and group travel time. The inclusion of thermal effect in group travel time causes a reduction in damping rate. The results are important in the study of the proton whistler propagating through the ionosphere.     

Ion-temperature-gradient driven modes in dust-contaminated plasma with nonthermal electron distribution and dust charge fluctuations

The effect of nonthermal electrons on ion-temperature-gradient (ITG) driven modes is investigated in the presence of variable dust charge and ion shear flow. The dust charge fluctuating expression is obtained in the presence of kappa distributed electrons. A dispersion relation is derived and analyzed numerically by choosing space plasma parameters of Jupiter/Saturn magnetospheres. It is found that the presence of nonthermal electrons population reduces the growth rate of ITG mode driven instability. The effects of ion temperature, electron density and magnetic field variation on the growth rate of ITG instability are presented numerically. It is also pointed out that the present results will be useful to understand the ITG driven modes with variable dust charge and kappa distributed electrons, present in most of the space plasma environments.     

New exact solutions for nonlinear solitary waves in Thomas-Fermi plasmas with (G′/G)-expansion method

The nonlinear propagation of ion acoustic waves in an ideal plasmas containing degenerate electrons is investigated. The Korteweg-de-Vries (K-dV) equation is derived for ion acoustic waves by using reductive perturbation method. The analytical traveling wave solutions of the K-dV equation investigated, through the (G′/G)-expansion method. These traveling wave solutions are expressed by hyperbolic function, trigonometric functions are rational functions. When the parameters are taken special values, the solitary waves are derived from the traveling waves. Also, numerically the effect different parameters on these solitary waves investigated and it is seen that exist only the compressive solitary waves in Thomas-Fermi plasmas.     

Obliquely propagating ion-acoustic waves in a magnetized electron-positron-ion plasma with trapped electrons

A theoretical investigation is carried out for understanding the basic features of oblique propagation of linear and nonlinear ion-acoustic waves subjected to an external magnetic field in an electron-positron-ion plasma which consists of a cold magnetized ion fluid, Boltzmann distributed positron, and electrons obeying a trapped distribution. In the linear regime, two dispersion curves are obtained. It is shown that the positron concentration causes the both modes to propagate with smaller phase velocities. Then, owing to the presence of resonant electrons, the modified Korteweg-de Vries equation describing the nonlinear dynamics of small but finite amplitude ion-acoustic waves is derived. It is found that the effects of external magnetic field (obliqueness), trapped electrons, positron concentration and temperature ratio significantly modify the basic features of solitary waves.