Title:

Wave propagation in equal mass plasmas

This thesis is concerned with wave propagation in equal mass plasmas. Equal mass plasmas have two components, both of the same mass but with opposite charges, and consequently they have a symmetry which is not present in the more usual electronion plasmas. This symmetry can be expected to lead both to a modification of results derived for electronion plasma, causing some phenomena to change, others to disappear and new phenomena to arise. With respect to the problem of wave propagation this is certainly the case. Equal mass plasmas are important in the laboratory and in astrophysics. In chapter one we briefly introduce the problem, firstly setting the scene by describing the 'Plasma Universe' and then introducing equal mass plasmas and mentioning a few molecular plasmas of this type. Chapter one is concluded with a review of the work done on electronpositron plasmas in astrophysics. Chapter two derives the equations needed to undertake the study of wave propagation in plasmas. We start from the most general description of the plasma as one point in Gamma Space and go on to derive the standard fluid equations. As we are dealing with an equal mass plasma, where both components are equally important, we derive the equations for a general multispecies plasma. In chapter three the problem of linear wave propagation in an equal mass plasma is tackled. We show that the special symmetry of equal mass plasmas simplifies the problem immensely, and that the well known phenomena of Faraday rotation and whistler wave modes are absent from the equal mass plasma. Dispersion relations are derived for the plasma in the cold and warm cases and the extension of equal mass symmetry to kinetic theory is discussed. Chapter four extends the work of chapter three to electronpositron plasmas. We discuss the validity of the models studied, the first of which considers the effect of the plasma being at a relativistic temperature (kT ≥ meC2). We then extend this model to incorporate, in a simple fashion, the effects of particle annihilation and creation in the plasma. In both cases we find that Faraday rotation is absent. In chapter five nonlinear plasma physics is introduced and its importance emphasised. We describe the solution of electrostatic plasma oscillations in a plasma of cold electrons and stationary ions. A numerical simulation is undertaken of the same problem for cold equal mass plasmas and, in stark contrast to the electronion case, a fundamental instability is found. A quasilinear analytic solution is found for the problem which corresponds well to the numerical results. Finally, in chapter six, we discuss extensions of the work in this thesis, in particular the generalisation of chapter five to warm plasmas. We also pose some related problems concerning equal mass and electronpositron plasmas.
