This thesis considers the propagation of accelerated electron beams in plasma. We consider the wave particle interactions these undergo which cause their evolution, the effects of plasma density inhomogeneities on these interactions, and the effects this may have on the production of hard X-ray and radio emission by the beam. Chapter 1 introduces the important background material on the Sun and solar flares, and some basic plasma physics. We discuss the acceleration and propagation of electrons beams and their production of hard X-ray emission, and the various observed types of radio emission from the Sun. We end by discussing details of the mechanism by which radio emission can be produced by beam generated Langmuir waves at GHz frequencies. Chapter 2 contains the mathematical derivation of the effects of plasma density fluctuations on Langmuir waves. This is found to be described by a diffusion of the waves in wavenumber space. We consider the situation in both one and three dimensions, for elastic and inelastic scattering of the Langmuir waves, discussing how our model expands on that previously considered in the literature, and develop a model for the fluctuations applicable to the electron beams we consider in this thesis. We derive the relevant diffusion coefficients for a few commonly observed density fluctuation spectra, then end with a brief discussion of the expected effects of the Langmuir wavenumber diffusion on the waves and electrons for a few representative cases. Chapter 3 uses the model derived in Chapter 2 in quasi-linear simulations of electron beam evolution. We consider two initial electron beam distributions, either a Maxwellian or a power law, and simulate the Langmuir wave generation and evolution, and the back-reaction of this on the electron beam. We find an electron acceleration effect to occur, and explore the parameters for which this is strongest. In addition we consider the production of hard X-ray emission from an initially power law beam, and the effects of the electron acceleration on this. Chapter 4 considers the radio emission from an electron beam via the generation of Langmuir waves. We first derive an angle-averaged model for emission at the second harmonic of the plasma frequency, and combine this with the simulations from the previous chapters. We include the effects of density fluctuations on the Langmuir waves, and discuss how this affects the radio emission produced. Chapter 5 concludes the thesis with a summary of the effects of density inhomogeneity on Langmuir waves, and consequently on fast electron beams and their hard X-ray and radio emissions in the solar corona. Appendix 1 contains the derivation of a mathematical model for radio emission from an electron beam at the fundamental of the local plasma frequency, which is unimportant in the parameter ranges considered in Chapter 4, but essential for radio bursts in the higher corona and solar wind.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:575967 |
| Date | January 2013 |
| Creators | Ratcliffe, Heather |
| Publisher | University of Glasgow |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://theses.gla.ac.uk/4442/ |
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