Effect of electrodynamic braking force localized on rational surfaces

The experimental observation of the association of the internal heat transport barriers in tokamaks with rational q surfaces is an open problem. Often the mechanism invoked for the onset of an internal transport barrier relies on the reduction of turbulence by a local increase of the E x B velocity shear. In this paper, we present in some detail the theoretical analysis of the possible role of an externally applied electrodynamic torque, resonant on a rational surface with the support of selected Joint European Torus experimental results.