**Drift Mode Calculations in Nonaxisymmetric Geometry**

Authors: G. Rewoldt, L.-P. Ku, W.M. Tang, and W.A. Cooper

**Date:** July 20, 1999

**Submitted:** Plasma of Physics

A fully kinetic assessment of the stability properties of toroidal drift modes has been obtained for nonaxisymmetric (stellarator) geometry, in the electrostatic limit. This calculation is a comprehensive solution of the linearized gyrokinetic equation, using the lowest-order "ballooning representation" for high toroidal mode number instabilities, with a model collision operator. Results for toroidal drift waves destabilized by temperature gradients and/or trapped particle dynamics are presented, using three-dimensional magnetohydrodynamic equilibria generated as part of a design effort for a quasiaxisymmetric stellarator. Comparisons of these results with those obtained for typical tokamak cases indicate that the basic trends are similar.