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Title: Collisional transport of trace impurity ions and the role of the radial electric field in spherical tokamak plasmas
Author: Wrench, Christopher G.
ISNI:       0000 0004 2739 9525
Awarding Body: University of Warwick
Current Institution: University of Warwick
Date of Award: 2012
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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.
Supervisor: Not available Sponsor: Engineering and Physical Sciences Research Council (EPSRC)
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: QC Physics