DRIFT WAVES IN PLASMAS WITH SHEARED FLOWS

In the standard approach to the problem of shear stabilization of drif t waves the diamagnetic drift velocity v() is regarded as a constant, which is usually not satisfied at the edge of a tokamak plasma. In co nfigurations of this type, with a steep density gradient and radially sheared transverse velocity field, the magnetic shear stabilization cr iteria are severely restricted, and the velocity profile curvature v ' '(0) (x) is found to play a crucial role. In the strongly nonlinear re gime, unstable drift waves may saturate into stationary coherent vorte x-type structures. The latter include a tripolar vortex. (C) 1998 Amer ican Institute of Physics. [S1070-664X(98)03312-6].