Test-particle simulations of collisional impurity transport in rotating spherical tokamak plasmas

Mckay, R.J., McClements, K.G., Thyagaraja, A. and Fletcher, L. (2008) Test-particle simulations of collisional impurity transport in rotating spherical tokamak plasmas. Plasma Physics and Controlled Fusion, 50(6), 065017. (doi:10.1088/0741-3335/50/6/065017)

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A full orbit test-particle approach is used to study the collisional transport of impurity (carbon) ions in spherical tokamak (ST) plasmas with transonic and subsonic toroidal flows. The efficacy of this approach is demonstrated by reproducing the results of classical transport theory in the large aspect ratio limit. The equilibrium parameters used in the ST modelling are similar to those of plasmas in the MAST experiment. The effects on impurity ion confinement of both counter-current and co-current rotation are determined. Various majority ion density and temperature profiles, approximating measured profiles in rotating and non-rotating MAST plasmas, are used in the modelling. It is shown that transonic rotation (both counter-current and co-current) has the effect of reducing substantially the confinement time of the impurity ions. This effect arises primarily because the impurity ions, displaced by the centrifugal force to the low field region of the tokamak, are subject to a collisional diffusivity that is greater than the flux surface-averaged value of this quantity (Helander 1998 Phys. Plasmas 5 1209). For a given set of plasma profiles, the ions are found to be significantly less well confined in co-rotating plasmas than in counter-rotating plasmas. The poloidal distribution of losses exhibits a pronounced up/down asymmetry that is consistent with the direction of the net vertical drift of the impurity ions.

Item Type:Articles
Glasgow Author(s) Enlighten ID:Fletcher, Professor Lyndsay
Authors: Mckay, R.J., McClements, K.G., Thyagaraja, A., and Fletcher, L.
College/School:College of Science and Engineering > School of Physics and Astronomy
Journal Name:Plasma Physics and Controlled Fusion
Publisher:Institute of Physics Publishing Ltd.
ISSN (Online):1361-6587
Published Online:19 May 2008

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