Shear flow generation due to electromagnetic instabilities

Saturation mechanism for electromagnetic instabilities such as resistive drift-Alfven modes (RDAMs) and resistive wall modes (RWMs) has been studied by solving nonlinear fluid model equations in cylindrical plasmas. For suppressing nonlinear growth of these modes poloidal shear flows are essential. However, the Maxwell stress due to magnetic fluctuations has a tendency to reduce the generation of poloidal flow and may change nonlinear behavior of these instabilities expected from linear properties. For weakly unstable RDAMs a stationary poloidal flow is achieved, although an oscillatory behavior is obtained for fairly unstable cases. For RWMs the Maxwell stress becomes dominant and an initial poloidal flow almost disappears near a rational surface particularly when a resistive wall is close to a main plasma. In case that the resistive wall is not close, stabilization of RWMs due to a poloidal flow remains. (author)