Parallel velocity shear instability, Alfven waves and the formation of thetransport barrier

It is suggested that the ponderomotive force induced by radio frequency (rf ) waves in the range of the Alfven frequency can create a transport barrier in a tokamak. The linear and nonlinear behavior of the driftlike perturbat ion with a parallel velocity shear is studied in the presence of rf waves. It is shown if the radial profile of the rf field energy is properly chosen the linear mode is stabilized and turbulent momentum transport reduces. Th e rf power required for this stabilization is found to be rather modest and hence should be easily obtained in actual experiments. (C) 2000 American I nstitute of Physics. [S1070-664X(00)03607-7].