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Collisional transport of trace impurity ions and the role of the radial electric field in spherical tokamak plasmas
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Wrench, Christopher G. (2012) Collisional transport of trace impurity ions and the role of the radial electric field in spherical tokamak plasmas. PhD thesis, University of Warwick.
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WRAP_THESIS_Wrench_2012.pdf - Submitted Version Download (9Mb) | Preview |
Official URL: http://webcat.warwick.ac.uk/record=b2661602~S1
Abstract
The mitigation and control of impurities, or non-fuel ions, in tokamak plasmas
is vital for reducing energy losses and an understanding of impurity transport is
required in order to predict the performance of present and future tokamak devices.
The development and application of a full orbit, test particle code to the study of the
collisional transport of test impurity ions in spherical tokamak plasmas is presented.
This code is tested against the standard analytic description of collisional transport
in magnetised plasmas and is demonstrated to be particularly suited to the study
of the tight aspect ratio of the spherical tokamak design.
The principle results of the present work concern the investigation of the
role of the radial electric field, a feature of high performance tokamak plasmas, on
collisional ion transport. It is found that a static radial electric field leads to a
significant reduction in the radial transport of test impurity ions. This effect may
be explained in terms of a novel radial drift of the test ions arising due to the
introduction of collisional Langevin terms to the full orbit, test particle equations
of motion. This has significant implications for the confinement of impurity ions in
high performance, steady state tokamak discharges. A scaling of this modification
with impurity particle mass and charge numbers is derived analytically and verified
numerically and a scaling with electric field parameters is derived numerically.
A time dependent radial electric field, which models a number of transient
events in tokamak plasmas such as the low- to high-mode transition and edge localised
modes, is also investigated and attempts at a preliminary comparison between
experimental and numerical observations of impurity transport in spherical
tokamak devices is presented.
Item Type: | Thesis (PhD) | ||||
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Subjects: | Q Science > QC Physics | ||||
Library of Congress Subject Headings (LCSH): | Tokamaks, Transport theory, Plasma dynamics, Electric fields | ||||
Official Date: | September 2012 | ||||
Dates: |
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Institution: | University of Warwick | ||||
Theses Department: | Department of Physics | ||||
Thesis Type: | PhD | ||||
Publication Status: | Unpublished | ||||
Supervisor(s)/Advisor: | Verwichte, E. (Erwin) | ||||
Sponsors: | Engineering and Physical Sciences Research Council (EPSRC) | ||||
Extent: | xiii, 124 leaves : charts. | ||||
Language: | eng |
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