TOROIDAL DRIFT WAVES IN THE PRESENCE OF FIELD-ALIGNED FLOWS

We investigate the effects of a radially varying field-aligned flow (which is very nearly equal to the toroidal flow) on the toroidal branch of drift waves. The role of velocity curvature is found to have robust effects on the radial structure of the mode. For a negative value of the curvature (usually found during the NBI heating), the radial mode envelope is much more extended than its conventional localised Gaussian structure and the mode becomes stable. Velocity shear, on the other hand, is found to have rather insignificant role both in determining the radial structure and stability.