Thesis--Ph. D., University of Hong Kong, 1977.

Thesis--M. Phil., University of Hong Kong, 1986.

The goal of this dissertation is to provide experimental insight into the mechanism behind the efficient power absorption of helicon plasmas. This work presents evidence which is consistent with the Radially Localized Helicon (RLH) theory put forth by Breizman and Arefiev. Helicon discharges produce peaked density profiles with radial density gradients creating a potential well that sets up the RLH waves, which we believe is the major power absorption mechanism in the plasma. The experimental data presented in this dissertation must be taken in totality along with parallel efforts in theory and computer simulation. We show photographic evidence along with Langmuir probe measurements of the axial density that shows an asymmetric, right-hand circularly polarized wave being launched in a direction consistent with RLH theory. Additionally, we are able to show, through Langmuir probe measurements, that significant radial density gradients exist in the plasma which is required by the RLH dispersion but contrary to the uniform density assumption of current theory. Furthermore, using the two-dimensional density profile obtained from experiment, we are able to use that data as input into a model which confirms key features of the power absorption in terms of location and magnitude. The time-varying magnetic field is measured and analyzed against the RLH dispersion relation. Using a Fourier decomposition technique, the analysis indicates the proper scaling of the wavenumbers with the RLH dispersion. Finally, using the experimental density as input to a computer model, simulations show very good agreement with the amplitude and phase of the experimentally measured RF magnetic fields. / text

published_or_final_version / Physics / Master / Master of Philosophy

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The behaviour of both small amplitude and arbitrary amplitude nonlinear electrostatic fluctuations are studied in electron-positron plasmas. The propagation characteristics of associated linear modes are also examined for selected plasma models. In the case of the four component, two-temperature, electron-positron plasma, three particular features are investigated. The first investigates existence conditions of the range of possible electrostatic linear waves that can propagate in a two-temperature electron-positron plasma, the study being particularly relevant to both astrophysical situations and laser induced fusion experiments. The second includes the development and investigation of the mKdV-ZK equation governing the three dimensional propagation of solitary waves in a magnetized plasma. The third application is the investigation of nonlinear electrostatic solitary waves structures, similar to those found in the broadband electrostatic noise observed in various regions of the earth’s magnetosphere. The study ends by considering relativistic effects on solitary waves in an electron-positron plasma. / Thesis (Ph.D.)-University of KwaZulu-Natal, Westville, 2009.