Effect of rotation and velocity shear on tearing layer stability in tokamak plasmas

Using a resistive generalization of the Frieman-Rotenberg formalism, the leading-order effects of velocity shear and rotation on linear tearing layer stability are studied for tokamak equilibria. The layer equations for resistive interchange modes are derived for arbitrary equilibrium rotation and velocity shear. The resulting layer equations do not conserve parity and are not simplified by Fourier transform. Thus, many standard numerical techniques cannot be implemented in a straightforward manner. Layer equations are also derived in the constant-Psi limit. The constant-Psi dispersion relation is obtained and is used to study the leading-order effects of rotation and velocity shear on the critical value of Delta' required for tearing instability. It is found that rotation and velocity shear can couple with the parallel current and the current gradient in the layer to reduce Delta(crit)'. If parallel currents are sufficiently weak to compete with second-order effects, velocity shear can be stabilizing, while rotation is found to have a destabilizing effect. Second-order coupling of velocity shear and rotation can have either sign, and thus can affect stability in either direction. (C) 2015 AIP Publishing LLC.