الفهرس 
IntroductionOnly 14 pages are availabe for public view
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Abstract
The research work of this thesis is about the study of the propagation and stability of wavepackets for some nonlinear acoustic waves in plasma. Since Maxwellian distribution is inadequate to describe several plasma environments, we have considered superthermal, q-nonextensive, and generalized (r,q) distributed particles for the present work. We have used multiple time scales method and derivative expansion method to derive nonlinear evolution equations.
In chapter two, we investigated the modulational instability (MI) of nonlinear ion acoustic waves (IAWs) in a weakly relativistic, warm, unmagnetized and adiabatic plasma whose constitutes are ion fluid and superthermally distributed electrons using the multiple scales approach. The basic set of equations is reduced to a finite wave number nonlinear Schrödinger-type equation. Moreover, the reductive perturbation technique is applied to the same system and a Korteweg-de Vries equation is obtained. For small wavenumber limit, it is found that the dispersion coefficient and nonlinear coefficient of the nonlinear Schrödinger-type equation are reduced to the coefficients of nonlinear Schrödinger-type equation obtained from Korteweg-de Vries (K-dV) equation. The dependence of the phase velocity and the group velocity as well as the stability domain on the ion-to-electron temperature ratio, the relativistic factor u_0/C and the superthermal parameter is investigated.
In chapter three, the MI of IAWs in a weakly relativistic warm adiabatic unmagnetized plasma and q-nonextensivelly distributed electrons, using the multiple scales is investigated. The stability domain is determined. The solution of ion acoustic rogue waves (IARWs) is presented. The effect of the physical parameters such as relativistic factor u_0/C and ion-to-electron temperature ratio 〖 T〗_i/〖 T〗_e (〖 T〗_i is the ion temperature and 〖 T〗_e is the electron temperature) as well as the distribution parameter q on the instability of the system and rogue wave (RW) characteristics; width and amplitude is studied.
In chapter four, a three-dimensional (3D) MI of dust acoustic waves (DAWs) in a three-component magnetized dusty plasma system consisting of a negatively charged fluid, inertialess generalized (r, q) distributed electrons and Boltzmann distributed ions, is investigated. The basic system of equations is reduced to a 3D nonlinear Schrödinger equation (NLS) which is valid for small but finite amplitude using the derivative expansion method. The domains of the stability and instability regions are investigated. It is found that they are strongly affected by the spectral parameters of the generalized (r, q) distribution and the electron-to-ion temperature ratio 〖 T〗_e/〖 T〗_i. The existence domains for observing the first-and second-order solutions of the dust acoustic rogue waves (DARWs) are determined and the basic features for the first-order solution are found to be significantly dependent on the system physical parameters changes such as 〖 T〗_e/〖 T〗_i, number density ratio [n_e0 / (n_d0 z_d0)] and the dust cyclotron frequency (ω_cd) as well as the spectral indexes r and q. A comparison between the first-and second-order DARW amplitudes is presented. Moreover, another comparison between the first-order DARW amplitudes obtained by generalized (r, q) distributed electrons and those corresponds to Maxwellian is provided. Finally, implications of our consequences in specific plasma situations are briefly discussed.