Chin, Robert (2012) Nonlinearity in thermally active and rotating plasmas. PhD thesis, University of Warwick.

Abstract

The wide reaching nature of plasma physics will be studied here, with the applications of both the large scale, of solar plasma physics and then decreasing by many orders of magnitude to the laboratory plasma, of magnetically confined fusion experiments. Part I The nonlinear evolution of magnetoacoustic waves in a nonadiabatic plasma are investigated analytically. The effect of plasma activity due to linear and quadratic heating and radiative cooling on propagating magnetoacoustic waves in a uniform plasma are considered. A non-linear evolution equation is derived and stationary solutions are looked for the various combination of signs of the linear and quadratic heating-cooling terms, which determine the thermal activity of the plasma. It is shown that self-organizing magnetoacoustic waves (autowaves) exist in an active plasma. These wave have amplitudes that are independent from the initial conditions and function of plasma properties only. Their potential diagnostic purposes are discussed. Furthermore, magnetoacoustic auto-solitary waves are shown to exist. They have been modelled using a novel perturbative technique which allows to determine their propagation speed and shape. Part II Equilibria of MAST-like plasmas with transonic toroidal flows are calculated numerically in the framework of two-fluid theory [Thyagaraja and McClements, 2006] using a fixedboundary equilibrium solver, GRASS.In the non-dissipative limit, with momentum sources neglected, two-fluid analysis leads to interdependence between the rotation, temperature and density profiles, and the possibility of a departure from rigid-body rotation of flux surfaces. The effects of toroidal flows on the position of the magnetic axis, the plasma safety factor profile and the density profile are determined for a range of scenarios, including rigid body rotation. The electron temperature and ion temperature are assumed to be flux functions, with profiles that are broadly consistent with measurements from MAST. This thesis will also highlight the differences, or indeed similarities, of plasma from the astrophysical to the laboratory world.

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