الفهرس 
IntroductionOnly 14 pages are availabe for public view
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Abstract
In this thesis, we started in chapter one the basic lines which include some definitions that would help to keep up with the whole thesis. In particular we discussed plasma definition and applications, ionosphere and nonlinear structures. Then in chapter two, we studied the properties of small amplitude nonlinear ion-acoustic solitary waves in a warm magneto plasma with positive and negative ions and nonthermal electrons. For this purpose, the hydrodynamic equations for the positive-negative ions, nonthermal electron density distribution, and the Poisson equation are used to derive the corresponding nonlinear evolution equation; Zkharov Kuznetsov (ZK) equation, in the small amplitude regime. The ZK equation is analyzed to examine the existence regions of the solitary pulses. It is found that the compressive and rarefactive ion-acoustic solitary waves strongly depend on the mass and density ratios of the positive and negative ions as well as the nonthermal electron parameter. Also, it is found that there are two critical values for the density ratio of the negative to positive ions, the ratio between unperturbed electron-to-positive ion density, and the nonthermal electron parameter, which decide the existence of positive and negative ion-acoustic solitary waves. Finally in chapter three, in the light of the pervious plasma system studied in chapter two, we investigated the effect off mass and density ratios of the positive and negative ions as well as the nonthermal parameter on the small amplitude double layers. The corresponding nonlinear evolution equation; modified Zkharov- Kuznetsov (MZK) equation, in the small amplitude regime is derived. It is found that the compressive and rarefactive double layers propagate in the current plasma system. The present study is applied to examine small amplitude nonlinear structures (i.e., ion-acoustic solitary excitations and double layers) for the and plasmas, where they are found in the D- and F-regions of the Earth’s ionosphere. This investigation should be helpful in understanding the salient features of the small amplitude nonlinear structures in space and laboratory plasmas where two distinct groups of ions and non-Boltzman distributed electrons are present.