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A novel asymptotic approach for solving the eigenvalue problem in the short-wavelength limit is developed. This approach, called the paraxial WKB method, is presented and applied to the analysis of gradient-driven instabilities in a tokamak. In some respects, the paraxial WKB method is more general than the ballooning representations usually used for this problem. For instance, the paraxial WKB method can describe drift-ballooning instabilities in the presence of sheared plasma rotation when the ballooning representation fails. Being different from other techniques, the paraxial WKB method not only sheds new light on the physics of drift-ballooning instabilities, but also provides a description for short-wave instabilities of other types. Other possible extensions of the paraxial WKB technique, such as the application to three-dimensional systems like stellarators, are briefly discussed. Finally, advantages and disadvantages of the paraxial WKB method in comparison with the ballooning representation are considered.

Additional information

Authors: PEREVERZEV G.V, Max-Planck-Institut fur Plasmaphysik, EURATOM Association (DE)
Bibliographic Reference: An article published in: Physics of Plasmas, Vol.8, No.8 (2001), pp:3664-33672
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