THEORY OF DRIFT WAVES IN THE PRESENCE OF PARALLEL AND PERPENDICULAR FLOW CURVATURE .1. SLAB MODEL

It has recently [S. Sen and M. G. Rusbridge, Phys. Plasmas 2, 2705 (19 95)] been shown that, contrary to the usual belief, parallel flow curv ature (V ''(H)) can stabilize drift-like microinstabilities. Here the earlier work is extended to include the effect of the perpendicular fl ow curvature (V ''(perpendicular to)), which is known to have a stabil izing role on the drift-like microinstabilities. The full analytic sta bility analysis shows that the ratio of the stabilizing influences of the perpendicular to the parallel flow curvature scales as L(s)/2L(n), where L(s) and L(n) are the magnetic shear and the density variation scale length, respectively. Thus, at the plasma edge (since L(s) much greater than L(n)) the perpendicular flow may play a crucial role in s tabilizing microinstabilities and turbulence in the improved regimes o f confinement [like the high (H) modes]. However, in the core confinem ent improvement [like the very high (VH) mode] both the parallel and t he perpendicular flow curvatures are important, since L(s) similar to 2L(n). Furthermore, as the confinement improvement in the core is usua lly related to the toroidal velocity and since V-parallel to coming fr om the toroidal flow is much more than V-perpendicular to (V-perpendic ular to similar to epsilon V-parallel to, here epsilon is the inverse aspect ratio), this implies that it is the parallel component of the t oroidal flow and not the perpendicular component, as is usually though t, which is responsible for the core confinement improvement. (C) 1996 American Institute of Physics.