Gingell, Peter W. (2013) Hybrid simulations of flow bursts in magnetically confined plasmas. PhD thesis, University of Warwick.

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Abstract

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.

Item Type:	Thesis (PhD)
Subjects:	Q Science > QC Physics
Library of Congress Subject Headings (LCSH):	Magnetic fields, Plasma (Ionized gases), Plasma density, Hybrid computer simulation
Official Date:	March 2013
Dates:	Date Event March 2013 Submitted
Institution:	University of Warwick
Theses Department:	Department of Physics
Thesis Type:	PhD
Publication Status:	Unpublished
Supervisor(s)/Advisor:	Chapman, Sandra C.; Dendy, R. O.
Sponsors:	Engineering and Physical Sciences Research Council (EPSRC) (EP/I501045); European Commission (EC); Research Councils UK (RCUK)
Extent:	xix, 146 leaves : illustrations.
Language:	eng

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