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The ideal magnetohydrodynamic stability properties of reactor-sized sphellamak and quasiaxisymmetric stellarator configurations with finite toroidal plasma current are investigated. In sphellamak systems, a peaked toroidal current profile yields maximum-B conditions in the central region of the plasma as a consequence of the paramagnetic enhancement of the magnetic field induced by the current. The resulting poloidally closed contours of the magnetic field strength prove instrumental in the favourable confinement predictions for alpha-particles. Under these conditions, the sphellamak is stable or weakly unstable to local Mercier or ballooning modes. As well as low order kink instabilities for volume average Beta* = 8%. Unfortunately, the bootstrap current calculated in the collisionless regime provides only a small fraction of the total plasma current that is required. In a two field-period quasiaxisymmetric reactor device, the bootstrap current in the collisionless limit can enhance the edge rotational transform when reactor relevant values of Beta* = 5% are approached. Global external kinks and internal resonant mode structures associated with the rational surface l = 1/2 can be destabilised. This effect is examined for various pressure profiles indicating the possibility of stabilisation via a judicious profile choice or modest counter current drive.

Additional information

Authors: NARUSHIMA Y ET AL, National Institute for Fusion Science, Toki (JP);COOPER W A, Centre de Recherches en Physique des Plasmas, Association EURATOM-Confédération Suisse, Ecole Polytechnique Fédérale de Lausanne (CH)
Bibliographic Reference: A paper given at the Joint Conference of the 12th International Toki Conference on Plasma Physics and Controlled Nuclear Fusion (ITC-12) and the 3rd General Scientific Assembly of Asia Plasma and Fusion Association (AFPA '01)
Availability: Published in: Journal of Plasma and Fusion Research Series, Vol 5 (2002), 57-62 Available free of charge from: École Polytechnique Fédérale de Lausanne (EPFL), Ecublens, CH-1015 Lausanne Fax +41-21-6934747
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