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The ideal magnetohydrynamic stability properties of 3-field period stellerator with quasiaxial symmetry features proposed by Garabedian and Ku are investigated. The stability limit imposed by local ballooning and Mercier modes allow beta~5.3% to be achieved by tailoring the pressure profile. For this system, we have developed a sequence of configurations that varies from the reference system proposed to the equivalent axisymmetric tokamak. A scan of kink stability reveals that the configuration with a plasma boundary shape that corresponds to 80% of the basic 3-period stellarator and 20% of the tokamak becomes marginal to global external modes. The normal magnetic field line curvature and the local magnetic shear play crucial roles in the stability properties. The local magnetic shear develops a helical stripe with increasing three-dimensional plasma deformation that inhibits the formation of the global structures. The normal magnetic field line curvature, however, becomes locally amplified by the three-dimensional plasma deformation in regions where the local magnetic shear vanishes. As a result, the susceptability to localized ballooning mode destabilization is enhanced.

Additional information

Authors: COOPER W A, Centre de Recherches en Physique des Plasmas, Ecole Polytechnique Federale, Lausanne (CH)
Bibliographic Reference: Article: Physics of Plasmas (2000)
Record Number: 200011777 / Last updated on: 2000-02-12
Original language: en
Available languages: en