Strongly localised concentrations or depressions of plasma density and magnetic field strength (\blobs") are ubiquitous in the edge region of tokamak fusion experiments. They contribute significantly to heating and transport in that region, and therefore to overall energy confinement. The existing fusion plasma literature in this area focuses primarily on blobs sufficiently large that a uid description is appropriate. However, the blob population may include some - not necessarily easily detectable - whose characteristic lengthscales are on the order of the ion gyro-scales. This implies that a description at the uid level is unlikely to capture the full dynamics. In this Thesis, therefore, we report hybrid (particle ions, uid electrons) particle-in-cell simulations of ion gyro-scale blobs, which enable us to examine the effects of finite Larmor radius on their dynamics, evolution, and their ability to heat the near-edge plasma. We find that ion gyro-scale blobs are advected with the background flow, and develop a twin-celled vortex structure. Asymmetry then arises from finite ion Larmor radius kinetics, manifesting in the size of the internal vortices, the shape of tails forming from blob ejecta, and the growth of a Kelvin-Helmholtz instability. Small scale blobs are also found to increase ion energies more than larger blobs as a result of ion pick-up at the upstream blob-background boundary, which may result in a significant increase in plasma energy caused by a blob population that is not yet directly observable. Finally, we examine the creation of ion gyro-scale blobs using hybrid simulations of kinetic interchange and Kelvin-Helmholtz instabilities, and present statistics of the sizes of blobs created by these instabilities, and power-laws for the resulting particle displacements.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:589810 |
| Date | January 2013 |
| Creators | Gingell, Peter W. |
| Publisher | University of Warwick |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://wrap.warwick.ac.uk/58230/ |
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