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Alfvén eigenmodes in magnetic X-point configurations with strong longitudinal fields

Published online by Cambridge University Press:  01 April 2009

N. BEN AYED ,
K. G. McCLEMENTS  and
A. THYAGARAJA
N. BEN AYED
Affiliation:
Department of Physics, University of York, Heslington, York YO10 5DD, UK (nizar.benayed@ukaea.org.uk)
K. G. McCLEMENTS
Affiliation:
EURATOM/UKAEA Fusion Association, Culham Science Centre, Abingdon, Oxfordshire OX14 3DB, UK
A. THYAGARAJA
Affiliation:
EURATOM/UKAEA Fusion Association, Culham Science Centre, Abingdon, Oxfordshire OX14 3DB, UK
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Abstract

A perturbative three-dimensional analysis is presented of Alfvén waves in a magnetic X-point configuration with a strong longitudinal guide field. The waves are assumed to propagate in the direction of the X-line, and both the plasma beta and equilibrium plasma current are taken to be zero. This provides a simple model of Alfvén wave propagation in the divertor region of tokamak plasmas. It is shown that the presence of the X-point places constraints on the structure of the leading-order (shear Alfvén) eigenfunctions. These eigenfunctions, and fast wave corrections to them, are determined explicitly for two cases. In the first of these the stream function for the shear Alfvén flow is azimuthally symmetric in the X-point plane and singular at the X-line; in the second case the stream function is largely confined to two quadrants in the X-point plane and is non-singular. For the latter scenario it is shown that coupling of the shear and fast waves is strongly localized to the vicinity of the separatrix.

Type
Papers
Information
Journal of Plasma Physics , Volume 75 , Issue 2 , April 2009 , pp. 203 - 215
Copyright
Copyright © Cambridge University Press 2008

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