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Abstract

The local ideal 3D MHD stability is studied for the Wendelstein 7-X configuration. A volume average beta limit of 5 % is found with a nearly optimal pressure profile using magnetic and geometric methods to calculate the parallel current density. The ballooning stability does not depend on the method of the parallel current calculation. In contrast, the value of the Mercier criterion depends sensitively on which method is used. Not only is the geometric method not sensitive to resonant surfaces, but there is a systematic error in the Mercier criterion for nonresonant surfaces when not enough modes are used to calculate the equilibria numerically with a spectral method. However, this systematic error does not change the average beta limit of W 7-X, because ballooning stability is more stringent than Mercier stability for this configuration.

Additional information

Authors: MOECKLI R, Centre de Recherches en Physique des Plasmas, Ecole Polytechnique Fédérale de Lausanne (CH);COOPER W A, Centre de Recherches en Physique des Plasmas, Ecole Polytechnique Fédérale de Lausanne (CH)
Bibliographic Reference: Report: LRP 483/93 EN (1993) 19 pp.
Availability: Available from Confédération Suisse, Centre de Recherches en Physique des Plasmas, Ecole Polytechnique Fédérale de Lausanne, 21 avenue des Bains, 1007 Lausanne (CH)
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