Casson, F. J. (Francis James) (2011) Turbulent transport in rotating tokamak plasmas. PhD thesis, University of Warwick.

Preview	PDF WRAP_Casson_orig_2011.pdf - Submitted Version - Requires a PDF viewer such as GSview, Xpdf or Adobe Acrobat Reader Download (4Mb)
Preview	PDF (Coversheet) WRAP_THESIS_coversheet_Casson.pdf - Other - Requires a PDF viewer such as GSview, Xpdf or Adobe Acrobat Reader Download (17Kb)

Abstract

Small scale turbulence in a magnetically confined fusion plasma drives energy and particle transport which determine the confinement. The plasma in a tokamak experiment has a toroidal rotation which may be driven externally, but can also arise spontaneously from turbulent momentum transport. This thesis investigates the interaction between turbulence and rotation via nonlinear numerical simulations, which use the gyrokinetic description in the frame that corotates with the plasma. A local gyrokinetic code is extended to include both the centrifugal force, and the stabilising effect of sheared equilibrium flow. Sheared flow perpendicular to the magnetic field suppresses the turbulence, and also breaks a symmetry of the local model. The resulting asymmetry creates a turbulent residual stress which can counteract diffusive momentum transport and contribute to spontaneous rotation. The competition between symmetry breaking and turbulence suppression results in a maximum in the nondiffusive momentum flux at intermediate shearing rates. Whilst this component of the momentum transport is driven by the sheared flow, it is also found to be suppressed by the shearing more strongly than the thermal transport. The direction of the residual stress reverses for negative magnetic shear, but also persists at zero magnetic shear. The parallel component of the centrifugal force traps particles on the outboard side of the plasma, which destabilises trapped particle driven modes. The perpendicular component of the centrifugal force appears as a centrifugal drift which modifies the phase relation between density and electric field perturbations, and is stabilising for both electron and ion driven instabilities. For ion temperature gradient dominated turbulence, an increased fraction of slow trapped electrons enhances the convective particle pinch, suggesting increased density peaking for strongly rotating plasmas. Heavy impurities feel the centrifugal force more strongly, therefore the effects of rotation are significant for impurities even when the bulk ion Mach number is low. For ion driven modes, rotation results in a strong impurity convection inward, whilst a more moderate convection outward is found for electron driven modes.

Item Type:	Thesis or Dissertation (PhD)
Subjects:	Q Science > QC Physics
Library of Congress Subject Headings (LCSH):	Plasma turbulence, Tokamaks
Date:	March 2011
Institution:	University of Warwick
Theses Department:	Department of Physics
Thesis Type:	PhD
Publication Status:	Unpublished
Supervisor(s)/Advisor:	Peeters, Arthur
Sponsors:	Engineering and Physical Sciences Research Council (EPSRC) ; Culham Centre for Fusion Energy (CCFE)
Extent:	vii, 147 leaves : ill., charts
Language:	eng
URI:	http://wrap.warwick.ac.uk/id/eprint/36765

Request changes to a record

Actions (login required)

View Item