KINETIC QUASITOROIDAL ION TEMPERATURE-GRADIENT INSTABILITY IN THE PRESENCE OF SHEARED FLOWS

The gyrokinetic integral equations for the study of the ion temperature gradient driven mode (eta(i) mode) in toroidal geometry, at low plasma pressure, are extended to include equilibrium ion parallel upsilon(0 parallel-to) (r) and perpendicular upsilon(E)(r) sheared flows, where r is the minor radius of the flux surface. Magnetic gradient and curvature drifts of the ions, as well as finite ion Larmor radius effects, are included. The parallel sheared flow is shown to be destabilizing. The perpendicular sheared flow is a stabilizing mechanism. Mixing length estimates show that the eta(i)-mode induced ion thermal transport increases with increasing parallel flow shear, and decreases with perpendicular flow shear. The decrease of the ion transport is due not only to the decrease of the mode growth rate, but also to the shrinking of the mode width. Using the mixing length formulas for the thermal transport associated with the unstable modes, it is shown that the results are consistent with the experimental observations concerning the improvement of confinement in H-mode discharges coincident with the increase of cross-field sheared flows.