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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 conditions for alpha particles. Under these conditions the sphellamak is stable or weakly unstable to local Mercier and ballooning modes as well as low order kink instabilities for volume average Beta*=8%. Unfortunately 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 t=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: COOPER W A, Centre de Recherches en Physique des Plasmas, Association EURATOM-Confederation Suisse, Ecole Polytechnique Federale de Lausanne (CH);ISAEV M Y, Russian Research Centre "Kurchatov Institute", Moscow (RU);OKAMURA S, National Institute for Fusion Science, Toki (JP);YAMAZAKI K, National Institute for Fusion Science, Toki (JP)
Bibliographic Reference: An article published in: Journal of Plasma Fusion Research, Vol. 5 (2002), pages 57-62.
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