Convective motions in the scrape-off layer of magnetically confined plasmas

Magnetic confinement devices utilize magnetic fields to confine hot plasma with the aim of generating thermonuclear fusion. At the plasma edge, in the so-called scrape-off layer (SOL), turbulent motions are responsible for transporting plasma from the core confinement region towards the material surfaces. It has been universally observed that SOL turbulence is characterised by large, intermittent fluctuations, often called filaments or blobs, which dominate the particle transport and enhance the plasma interaction with the surrounding material boundaries. This is problematic as plasma-wall interaction can potentially damage plasma-facing components and shorten the life-time of the device. A full understanding of filament dynamics is therefore essential for the successful operation of future fusion experiments and reactors.

The dominant mechanism behind the generation of turbulent motions at the plasma edge is thought to be the interchange instability, due to pressure gradients and magnetic field curvature. In this thesis we study a two-dimensional interchange model based on the Braginskii fluid equations, in an effort to shed light on the fundamental properties of the onset of instability. We study interchange dynamics in two different settings: first, we restrict our attention solely to the dynamics in the SOL; next, we extend our considerations to the coupled interaction between the core plasma and the SOL. In both cases we characterise the onset of instability and perform an extensive analysis to describe how the behaviour of the system varies as a function of plasma parameters.