Mouloud Tribeche

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 experi...

Variable charge dust acoustic solitary waves in a dusty plasma with a q-nonextensive electron velocity distribution

A first theoretical work is presented to study variable charge dust acoustic solitons within the theoretical framework of the Tsallis statistical mechanics. Our results reveal that the spatial patterns of the variable charge solitary wave are significantly modified by electron nonextensive effects. In particular, it may be noted that for −1 1 provides qualitatively opposite results: electron nonextensivity makes the solitary structure more spiky. Our results should help in providing a go...

Electron-acoustic solitary waves in a nonextensive plasma

The problem of arbitrary amplitude electron-acoustic solitary waves (EASWs) in a plasma having cold fluid electrons, hot nonextensive electrons, and stationary ions is addressed. It is found that the “Maxwellianization” process of the hot nonextensive component does not favor the propagation of the EASWs. In contrast to superthermality, nonextensivity makes the electron-acoustic solitary structure less spiky. Our theoretical analysis brings a possibility to develop more refined theories of nonlinear solitary structures in astrophysical plasmas.

Modulational instability of ion-acoustic waves in a plasma with a q-nonextensive electron velocity distribution

The modulational instability (MI) of ion-acoustic waves (IAWs) in a two-component plasma is investigated in the context of the nonextensive statistics proposed by Tsallis [J. Stat. Phys. 52, 479 (1988)]. Using the reductive perturbation method, the nonlinear Schrodinger equation (NLSE) which governs the MI of the IAWs is obtained. The presence of the nonextensive electron distribution is shown to influence the MI of the waves. Three different ranges of the nonextensive q-parameter are considered and in each case the MI sets in under different conditions. Furthermore, the effects of the q-parameter on the growth rate of MI are discussed in detail.

Charging of a dust particle in a plasma with a non extensive electron distribution function

We present a theoretical model for the electrostatic charging of a spherical dust particle in an electron-ion plasma with streaming ions and a nonextensive electron distribution function following a non-Maxwell-Boltzmann law. The non-extensive electron distribution function drastically affects the electron current to dust grain surface and, therefore, the electron charge on a dust particle is significantly reduced in a non-Maxwellian dusty plasma.

Small amplitude ion-acoustic double layers in a plasma with superthermal electrons and thermal positrons

Small-amplitude ion-acoustic double layers (IA-DLs) in a plasma with superthermal electrons and thermal positrons are investigated. Due to the electron superthermality and the relative fraction of positrons, our plasma model can admit compressive as well as rarefactive IA-DLs. As the electrons evolve toward their thermodynamic equilibrium, the negative IA-DL shrinks and, beyond a certain critical value of the electron spectral index κc, develops into a positive structure allowing therefore the existence of compressive IA-DLs. This critical value is lowered as the number of positrons becomes important. As the superthermal character of the plasma increases, the threshold pc above which only compressive IA-DLs are admitted is shifted toward higher values. Our investigation may help to understand the DL structures observed in the ionosphere and the auroral acceleration regions.

Nonlinear ion-acoustic solitary waves in electronegative plasmas with electrons featuring Tsallis distribution

Weakly nonlinear ion-acoustic (IA) solitary waves, which accompany electronegative plasmas composed of positive ions, negative ions, and nonextensive electrons are investigated. Allowing for electrons departure from Boltzmann’s distribution is shown to bear considerable new features of the IA soliton characteristics. Three different types of electronegative plasmas inspired from the experimental studies of Ichiki et al. [Phys. Plasmas 8, 4275 (2001)] are discussed, and the dependence of IA solitons basic characteristics on physical parameters is also investigated. It is found that for certain values of the negative-to-positive ion density ratio, ν, the positive-to-negative ion mass ratio, Q, and the nonextensive parameter, q, the plasma system supports rarefactive solitons.

Effects of electron depletion on nonlinear dusty plasma oscillations

A kinetic analysis of the excitation of dust BGK (Bernstein–Greene–Kruskal) modes in a noncollisional dusty plasma is presented. It is found that in the case where all the electrons are attached to the dust particles, consequent modifications in the electrostatic potential structure can significantly influence the existence and properties of the nonlinear BGK modes. The derivation goes parallel to that done in standard kinetic analysis.

Ion acoustic solitary waves in a plasma with superthermal electrons and positrons

The problem of arbitrary amplitude ion acoustic solitary waves in a plasma with Boltzmann distributed positrons and superthermal electrons is addressed. The domain of their allowable Mach numbers is shifted towards lower values as the positron-to-electron density ratio p is increased. Beyond a certain critical value of p only subsonic ion-acoustic solitons are admitted. This threshold for the onset of subsonic ion-acoustic solitons is lowered as the superthermal character of the plasma is increased. In the limit of small spectral index κ, the ion-acoustic solitons are subsonic over the entire range of p. Cusped ion-acoustic solitons may arise as the electrons evolve far away from their thermodynamic equilibrium. Our results should help to understand the localized structures that may occur in space plasmas.

Debye shielding in a nonextensive plasma

The phenomenon of Debye Shielding is revisited within the theoretical framework of the Tsallis statistical mechanics. The plasma consists of nonextensive electrons and ions. Both the effective Debye length λDq and the fall-off of the electrostatic potential Φ are considered and a parameter study conducted. Owing to electron nonextensivity, the critical Mach number derived from the modified Bohm sheath criterion may become less than unity allowing therefore ions with speed less than ion-acoustic speed to enter the sheath from the main body of the plasma. Considering the wide relevance of collective processes, our analysis may be viewed as a first step toward a more comprehensive Debye shielding and electrostatic plasma sheath in nonequilibrium plasmas.