Abstract
The two-dimensional eigenvalue equation for electrostatic drift waves in axisymmetric toroidal geometry is investigated. A model version, relevant for the Culham levitron, is constructed, and solutions are obtained when poloidal variations of shear, curvature and magnetic field are included. General criteria for the existence of localized undamped eigenmodes are established, and it is found that for sufficiently strong modulations of various equilibrium quantities, the stabilizing effect of magnetic shear is completely nullified. Equivalent criteria are obtained for the large-aspect-ratio tokamak. Investigation of the electron Landau resonance in strongly modulated magnetic fields indicates that for electron drift waves the growth rate will be only logarithmically weaker than in the equivalent slab-model calculation.
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