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Linear and nonlinear fluctuations in multicomponent plasmas applied to magnetospheric environments.

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In this thesis, we discussed the linear and nonlinear effects in multicomponent plasmas. By multicomponent, we refer to electron-positron-ion and electron-positron-dust type plasmas. The linear electrostatic waves in magnetized three-component electron-positron-ion plasmas consisting of cool ions, and hot Boltzmann electrons and positrons have been investigated in the low-frequency limit. By using the continuity and momentum equations with the Poisson equation, the dispersion relation is derived. Two stable modes of the waves are investigated in different cases, viz parallel and perpendicular propagation. The effects of the density and the temperature ratio on the wave structures are investigated. We also studied the behavior of the nonlinear electrostatic waves: first, we consider the electrons and positrons as having Boltzmann density distributions and the ions being governed by the fluid equations, and second we extend our model by assuming that all species are governed by the fluid equations. The set of nonlinear differential equations is obtained and this set is numerically solved for the electric field. The numerical solutions exhibit the range of period varying from sinusoidal to sawtooth to spiky waveforms. The effects of the driving electric field, temperature, concentration, drift velocity, Mach number and propagation angle on the wave structures are investigated. Finally, the study ends by investigating solitary waves in an electron-positron-dust plasma. The arbitrary amplitude dust acoustic solitary waves has been studied by using Sagdeev pseudopotential approach in a plasma consisting of hot electrons and positrons, and cold dust grains. The conditions of the existence of solitons are found assuming constant dust charge.


Doctor of Philosophy in Chemistry. University of KwaZulu-Natal, Durban 2015.