student profile: Mr James Harding


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Thesis work

Thesis title: 3D simulation of the quasilinear electron-Langmuir wave interaction in type III solar radio bursts

Supervisors: Iver CAIRNS , Donald MELROSE

Thesis abstract:

Type III solar radio bursts are the most frequent and intense radio emissions from the Sun, and are an important tool to better understand the physics of the solar corona from the surface of the Sun to the Earth and beyond. They give vital data about both long term characteristics of this environment and transient events like solar flares and coronal mass ejections. Most significantly, they provide a way to understand and motivate the study of the fundamental physics behind the interaction of electrons and Langmuir waves - one of the most basic and important systems in plasma physics, space science and astrophysics.

Type III bursts are driven by fast electron beams which are accelerated in solar flares and propagate from the Sun through the heliosphere. This beam interacts with the background plasma, generating Langmuir waves which are converted by nonlinear wave-wave processes to electromagnetic waves at the plasma frequency and its second harmonic. The electron-Langmuir wave interaction in the solar corona is governed by a set of quasilinear equations which are computationally difficult and intensive. At the University of Sydney, a type III simulation code has been developed that simulates the quasilinear interaction and the production of radio waves separately. This code currently describes the electron-Langmuir wave interaction for a one-dimensional system. The 1D electron beam and Langmuir wave distribution is then projected into three dimensions using an assumed angular dependence, and the nonlinear processes are numerically simulated to produce type III dynamic spectra. The 1D approximation is believed to have serious limitations and a fully 3D numerical simulation is required. This project will develop the first fully 3D axisymmetric simulation of the quasilinear interaction, in order to determine the limits of the validity of the 1D approximation and to capture intrinsically-3D effects. This 3D simulation will then be used with the existing radio emission code to predict realistic type III radio spectra, which will form the only such complete numerical simulation in the world.

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