RADIAL EXTENSION OF DRIFT WAVES IN THE PRESENCE OF VELOCITY PROFILES

The effect of a radially varying poloidal velocity field on the recently found radially extended toroidal drift waves [Connor et al., Phys. Rev. Lett. 70, 1803 (1993)] is investigated analytically. The role of velocity curvature (V″θ) is found to have robust effects on the radial mode structure of the mode. For a positive value of the curvature [usually found in the high-(H) mode edges] the radial mode envelope, similar to the sheared slab case, becomes fully outgoing. On the other hand, for a negative value of the curvature [usually observed in the low-(L) mode edges] the characteristics of conventional drift waves return back. The radial mode envelope reduces to a localized Gaussian shape and the mode can be unstable again for typical (magnetic) shear values in tokamaks. Velocity shear (V′θ) on the other hand is found to have a rather insignificant role both in determining the radial mode structure and the stability. © 1995 American Institute of Physics.