Test Particle Transport in Turbulent Magnetohydrodynamic Structures
Cristian-Constantin Lalescu
Turbulent phenomena are found in both natural (e.g. the Earth’s oceans, the Sun’s corona) and artificial (e.g. flows through pipes, the plasma in a tokamak de- vice) settings; evidence suggests that turbulence is usually the normal behaviour in most cases. Turbulence has been studied extensively for more than a century, but a complete and consistent theoretical description of it has not yet been pro- posed. It is in this context that the motion of particles under the influence of turbulent fields is studied in this work, with direct numerical simulations.
The thesis is structured in three main parts. The first part describes the tools that are used. Methods of integrating particle trajectories are presented, together with a discussion of the properties that these methods should have. The simula- tion of magnetohydrodynamic (MHD) turbulence is discussed, while also intro- ducing fundamental concepts of fluid turbulence. Particle trajectory integration requires information that is not readily available from simulations of turbulent flows, so the interpolation methods needed to adapt the fluid simulation results are constructed as well.
The second part is dedicated to the study of two MHD problems. Simulations of Kolmogorov flow in incompressible MHD are presented and discussed, and also simulations of the dynamo effect in compressible MHD. These two scenarios are chosen because large scale structures are formed spontaneously by the turbulent flow, and there is an interest in studying particle transport in the presence of structures.
Studies of particle transport are discussed in the third part. The properties of the overall approach are first analyzed in detail, for stationary predefined fields.
Focus is placed on the qualitative properties of the different methods presented.
Particle transport in frozen turbulent fields is then studied, and Results concern- ing transport of particles in fully developed, time-evolving, turbulent fields are presented in the final chapter.
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