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Title: Nonlinear electrostatic excitations in multi-component plasmas
Author: Sultana, Sharmin
ISNI:       0000 0004 2745 1389
Awarding Body: Queen's University Belfast
Current Institution: Queen's University Belfast
Date of Award: 2012
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The work carried out in the thesis demonstrates the non linear aspects of electrostatic solitary and shock waves in multi-component plasmas, characterised by excess superthermal electrons, via the fluid theory. The electrons superthermality is modeled through the kappa type distribution function. The properties of amplitude modulated wavepackets and the occurrence of modulational instability is investigated in detail in a collisionless plasma. The plasma superthermality and the concentration of superthermal electrons may control or even suppress the modulational instability. The stability of bright and dark-type non linear structures is confirmed by numerical simulations. The nonlinear properties of electrostatic solitary waves are investigated off equilibrium via the long wavelength approximation. The nonlinearity and dispersion terms, as well the energy acquired by electrostatic solitons for different nonthermality are discussed. The soliton is found to convert into multi-solitons or loses its energy via random oscillations while crossing the interface between two plasma regions with different superthermality characteristics. The solitary wave characteristics are investigated in a magnetised plasma via non-perturbative method. An investigation of the soliton propagation characteristics and existence domain, in terms of the soliton speed (Mach number) are presented. The effect of obliquity (angle between the wave propagation vector and the magnetic field) and as well as of magnetic field effect are discussed. The basic features and the underlying physics of electrostatic solitary waves, which are relevant to space and laboratory plasmas, are briefly discussed. Finally, taking into account dissipation via the fluid kinematic viscosity, characteristics of electrostatic shocks are discussed. Small perturbation near equilibrium, i.e., off equilibrium is assumed to analyse the shock wave properties in an unmagnetised kappa distributed nonthermal plasma. The stability of the shock profile is analysed analytically and numerically. The stability conditions are discussed for the theoretical framework of kappa superthermal plasma.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available