Rarefactive Ion-acoustic Solitons Research Articles

Compressive and rarefactive ion-acoustic solitons in a magnetized quantum plasma

Compressive and rarefactive ion-acoustic solitary waves (IASWs) in a magnetized, collisionless, three-component, dense plasma system have been carried out. The plasma system is assumed to be composed of non-degenerate inertial ions, degenerate electrons and immobile positively charged heavy ions. The magnetized Korteweg-de Vries (K-dV) and modified K-dV (mK-dV) equations are derived by adopting reductive perturbation method to study the basic characteristics of IASWs. It is seen that the effects of degenerate pressure, number density of electrons, inertial ions, and positively charged static heavy ions significantly modify the fundamental features of IASWs. It is also found that the magnetic field (obliqueness) has a significant contribution on the characteristics of IASWs. The implication of our results in some space and laboratory plasma situations are concisely discussed.

Compressive and rarefactive ion acoustic solitons in a magnetized two-ion component plasma

The formation of compressive (hump) and rarefactive (dip) ion acoustic solitons is studied in magnetized O+- H+- e and O+- H−- e plasmas. The hydrodynamics equations are described for cold heavy (oxygen) ions, warm light (hydrogen) ions and isothermal Boltzmann distributed electrons along with Poisson equations in the presence of a magnetic field. The reductive perturbation method is used to derive the nonlinear Zakharov–Kuznetsov (ZK) equation for an ion acoustic wave in magnetized two-ion component plasma. It is found that two modes of ion acoustic waves with fast and slow speeds can propagate in the linear limit in such a plasma. It is noticed that, in the case of positively charged light hydrogen ions O+- H+- e plasmas, the slow ion acoustic wave solitons formed both potential hump as well as dip structures, while fast ion acoustic wave solitons give only hump structures. However in the case of negatively charged light hydrogen ions O+- H−- e plasmas, the slow ion acoustic wave solitons formed potential hump structures while fast ion acoustic wave solitons produce dip structures. The variations in the amplitude and width of the nonlinear slow and fast ion acoustic wave structures with density, temperature of light ions and magnetic field intensity are obtained in magnetized two-ion component plasmas. The magnetic field has its effect only on the width of the nonlinear ion acoustic wave structures in two-ion component plasmas.

Linear and nonlinear obliquely propagating ion-acoustic waves in magnetized negative ion plasma with non-thermal electrons

AbstractIon-acoustic solitons in magnetized low-β plasma consisting of warm adiabatic positive and negative ions and non-thermal electrons have been studied. The reductive perturbation method is used to derive the Korteweg–de Vries (KdV) equation for the system, which admits an obliquely propagating soliton solution. It is found that due to the presence of finite ion temperature there exist two modes of propagation, namely fast and slow ion-acoustic modes. In the case of slow-mode if the ratio of temperature to mass of positive ion species is lower (higher) than the negative ion species, then there exist compressive (rarefactive) ion-acoustic solitons. It is also found that in the case of slow mode, on increasing the non-thermal parameter (γ) the amplitude of the compressive (rarefactive) soliton decreases (increases). In fast ion-acoustic mode the nature and characteristics of solitons depend on negative ion concentration. Numerical investigation in case of fast mode reveals that on increasing γ, the amplitude of compressive (rarefactive) soliton increases (decreases). The width of solitons increases with an increase in non-thermal parameters in both the modes for compressive as well as rarefactive solitons. There exists a value of critical negative ion concentration (αc), at which both compressive and rarefactive ion-acoustic solitons appear as described by modified KdV soliton. The value of αc decreases with increase in γ.

Ion-acoustic solitary waves in a plasma with a q-nonextensive electron velocity distribution

Arbitrary amplitude ion-acoustic solitary waves are addressed in a two-component plasma with a q-nonextensive electron velocity distribution. Our results show that in such a plasma solitary waves, the amplitude and nature of which depend sensitively on the q-nonextensive parameter can exist. Due to the electron nonextensivity, our plasma model can admit compressive as well as rarefactive ion-acoustic solitons. For q>1 (−1<q<1), the lower limit of the allowable Mach numbers is smaller (greater) than its Boltzmannian counterpart, allowing therefore the possibility of the existence of subsonic ion-acoustic solitons. As the nonextensive character of the plasma becomes important, the potential pulse amplitude increases while its width is narrowed. For −1<q<0, our plasma model can admit only rarefactive ion-acoustic solitary waves involving relatively high Mach numbers. Due to the flexibility provided by the nonextensive q-parameter, our results should help in providing a good fit between theoretical and experimental results.

Compressive and rarefactive ion-acoustic solitons in a two component electron plasma

In this paper an analysis is given for the conditions under which compressive and rarefactive ion-acoustic solitons may exist in a plasma containing two electron populations, one hot and the other cool. Compressive solitons exist in the collective Mach number range 1 < M < M c , which, for a given abundance ratio of the cool population translates into an annular region in the ion-acoustic Mach numbers space. The upper limit M c corresponds to a degenerate sonic point for the protons in which they tend to an infinite compression and are brought to rest at the wave centre. To form a charge neutral point in the rarefactive regime (a prerequisite to the existence of rarefactive solitons) it is necessary that the 'scale height of the hot electrons be sufficiently large that their number density, which is nearly constant. approximately balances that of the protons, before the cool electrons experience their 'atmospheric lid'. Furthermore, a sufficient condition for the existence of rarefactive solitons is found by requiring a solution to the wave structure equation at the 'lid'. The case of very hot electrons (highly sub-ion-acoustic) is considered. and various parameter regimes in which compressive and rarefactive solitons exist are evaluated in this super-hot electron approximation, both for the polytropic case γ ¬= 1. and the isothermal case, γ = 1. This approximation is formally equivalent to the problem of a bi-ion plasma, including a super-massive negative species.

A study of ion-acoustic solitons and double layers in a multispecies collisionless weakly relativistic plasma

The effect on the propagation of ion-acoustic solitons and double layers has been studied in collisionless weakly relativistic plasma consisting of two-electron temperature with isothermal electrons and finite ion temperature. The Korteweg de-Vries (KdV) equation is derived for ion-acoustic solitons propagating in a collisionless plasma. This equation is solved in a stationary frame to obtain the expression for soliton phase velocity, soliton width and peak soliton amplitude. It is observed that these quantities are significantly influenced by the relativistic effect, ion temperature, low-temperature electron density and ratio of cold to hot electron temperatures. Many features expected from hot ion theory and two species electron plasmas automatically emerge. The analysis is further extended to higher order nonlinearity and modified Korteweg de-Vries (mKdV) equation is derived. Even though compressive and rarefactive ion-acoustic solitons are obtained, only rarefactive ion-acoustic double layers are obtained in the present investigation.

Compressive and rarefactive ion-acoustic solitons in bi-ion plasmas

Nonlinear propagation of ion-acoustic solitary structures in plasmas with an admixture of heavy ions is studied in the wave frame, where they are stationary, using a recently developed gas-dynamic approach, as an alternative to the conventional Sagdeev pseudopotential method. This viewpoint brings out the gas-dynamic aspects, which then allow a characterization of the solitary wave structures in terms of the species’ sonic points, the global charge neutral points, and critical collective Mach numbers. It is shown that the concepts of a critical density in the Korteweg–de Vries (KdV) treatment, and of a changeover from compressive to rarefactive soliton character, correspond to the formation of a second charge neutral point (outside equilibrium) in the rarefactive regime, at which the electric stresses maximize. It is possible therefore that in certain regions of parameter space compressive and rarefactive solitons can co-exist. The compressive solitons are not predicted by a weakly nonlinear KdV treatment, except very close to the changeover region at sufficiently small enough amplitudes, as typified by the “modified” KdV (mKdV) equation. Their prediction requires a fully nonlinear treatment. Existence criteria are deduced and evaluated numerically in the parameter space of soliton Mach number and normalized density of the heavy species for compressive and rarefactive ion-acoustic solitons in a plasma with negative ion admixture.

Ion-acoustic solitons in a plasma with a relativistic electron beam

Ion-acoustic solitons in a collisionless plasma consisting of warm ions, hot isothermal electrons, and a relativistic electron beam are studied by using the reductive perturbation method. The basic set of fluid equations is reduced to Korteweg–de Vries (KdV) and modified Korteweg–de Vries (mKdV) equations. The effects of ion temperature and relativistic electron beam on ion-acoustic solitons are investigated. It has been shown that the four ion-acoustic modes can be propagated in this plasma system. The compressive and rarefactive ion-acoustic solitons satisfies the KdV equation for a given soliton velocity, beam density much smaller than the background electron density and the bulk ion temperature smaller than the background electron temperature for two modes. Also it has been illustrated that there exist mKdV solitons for some critical value of electron beam density in these cases. These critical values decrease as ion temperature increases for one of two modes and increase for the other one. Finally, it has been remarked that for another two modes only rarefactive KdV ion-acoustic solitons can be obtained. One of these modes exists for the electron beam density much smaller than the bulk electron density, and the other exists for almost all values of the beam density, even if it is greater than the background electron density.

Ion-acoustic solitons and double layers in a two-electron temperature plasma with hot isothermal electrons and cold ions

It is found that a two-electron temperature plasma with isothermal electrons and cold ions admits both compressive and rarefactive solitons, as well as compressive and rarefactive double layers (depending on the concentration of low-temperature electrons). In this paper, a Korteweg–de Vries (K-dV) equation and a K-dV-type equation with cubic and fourth-order nonlinearity at the critical density of the low-temperature isothermal electrons are derived to discuss the properties of ion-acoustic solitons in a two-electron temperature plasma. In the vicinity of the critical electron density of low-temperature isothermal electrons, we have derived a K-dV-type equation with mixed nonlinearity, and the solution of this equation will have both compressive and rarefactive double layers for those values of critical electron density of low-temperature electrons for which ion-acoustic solitons do not exist. By using quasipotential analysis, critical Mach numbers M1c and M2c are obtained such that compressive ion-acoustic solitons exist when 1&amp;lt;M&amp;lt;M1c and rarefactive ion-acoustic solitons exist when 1&amp;lt;M&amp;lt;M2c.

Oblique collision of plane ion acoustic solitons in a multicomponent plasma with negative ions

The resonant interaction of compressive and rarefactive ion acoustic solitons is studied experimentally in a multicomponent plasma containing additional negative-ion species. With increasing concentration of negative ions, the resonance amplitude increases for compressive ion acoustic solitons when the angle of collision is fixed. When the negative-ion concentration is larger than a critical value, the rarefactive ion acoustic solitons undergo resonant interaction for a lower resonance amplitude. Theoretical predictions of the Korteweg–de Vries equation agree with experimental findings.

Rarefactive ion acoustic soliton excitation using a modulated high-frequency sinusoidal wave in a negative ion plasma

Experiments on the excitation of rarefactive ion acoustic solitons using a fine mesh grid in a negative ion plasma are described. The excitation is novel in that a modulated high-frequency sinusoidal wave voltage signal is applied to the grid. An interpretation of the velocity modulation and bunching of free-streaming ions that pass through the grid to which the signal is applied is given.

Reflection of modified Korteweg-de Vries solitons in a plasma having negative ions

The variable coefficient modified Korteweg-de Vries (mKdV) equations for incident and reflected solitons are derived and solved to study the reflection of compressive and rarefactive ion acoustic solitons at the critical density in an inhomogeneous negative ion plasma. The polarity of the incident compressive and rarefactive solitons is not altered during the reflection process. Increasing the density gradient reinforces the reflection of both compressive and rarefactive mKdV solitons, whereas enhancement of the unperturbed plasma density weakens the reflection.

Reflection of ion acoustic solitons in a plasma having negative ions

Reflection of compressive and rarefactive ion acoustic solitons propagating in an inhomogeneous plasma in the presence of negative ions is investigated. Modified Korteweg–de Vries equations for incident and reflected solitons are derived and solved. The amplitude of incident and reflected solitons increases with negative to positive ion density ratio. With increasing density ratio, reflection of rarefactive solitons is reinforced whereas that of compressive solitons weakened. The rarefactive solitons are found to undergo stronger reflection than the compressive ones.

Excitation of ion-acoustic rarefactive solitons in a two-electron-temperature plasma

Rarefactive ion-acoustic solitons have been observed in a two-electron-temperature plasma. Some of the characteristics can be interpreted by the solution of the Kortweg–de Vries (K–dV) equation. The Mach number of the solitons is a function of the temperature ratio of hot and cold components.