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Investigations of the MAST SOL using the reciprocating probe system

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Title: Investigations of the MAST SOL using the reciprocating probe system
Authors: Tallents, Sebastian
Item Type: Thesis or dissertation
Abstract: Parallel flow in the scrape-off layer is a major area of interest in tokamak research, impacting on impurity transport, tritium retention and H-mode access. The work presented here is the first major investigation of SOL flow in the Mega Ampere Spherical Tokamak (MAST), using a Gundestrup probe specifically designed for the task. The results of a parameter scan in poloidal field, Bѳ, and temperature, T, of parallel velocity at the outboard mid-plane are presented, and the results and scalings compared to B2SOLPS5.0 simulations of MAST and a simple analytical model, in order to identify the relative importance of drift mechanisms (such as Pfirsch-Schluter and E × B) for driving parallel flow. The results show the predicted linear scaling with temperature and poloidal field strength, but also suggest a density dependence. Another major are of interest is the discovery in recent years of coherent filamentary structures that are radially convected through the L-mode SOL. These filaments are believed to contain sharp gradients in temperature, density and plasma potential, complicating probe analysis. An investigation to characterise the intermittency of the MAST SOL, it’s dependencies on poloidal field strength, density or temperature, and the impact of the filaments on probe measurements was also carried out, and a probe was built to further investigate the structure and dynamics of the filaments. Based on these experiments a method for resolving the flow in the filaments and background plasma was developed and applied in the flow experiments described above. It is found that the parallel Mach numbers are lower in the filaments than the ambient plasma in the far SOL — suggesting either ion temperatures are at least on the order of 4 times the electron temperature — or parallel flow velocity is substantially lower in the filaments than in the background plasma.
Issue Date: Jan-2009
Date Awarded: Aug-2009
URI: http://hdl.handle.net/10044/1/5292
DOI: https://doi.org/10.25560/5292
Supervisor: Coppins, Michael
Sponsor/Funder: United Kingdom Engineering and Physical Sciences Research Council and by the European Communities under the Contract of Association between EURATOM and UKAEA
Author: Tallents, Sebastian
Department: Physics
Publisher: Imperial College London
Qualification Level: Doctoral
Qualification Name: Doctor of Philosophy (PhD)
Appears in Collections:Physics PhD theses



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