Stability of resistive wall modes in reversed field pinches with longitudinal flow and dissipative effects

The stability of the nonresonant external kink modes in a reversed field pinch (RFP) under resistive wall boundary conditions is investigated. The effects of toroidal plasma rotation and parallel viscosity, as well as the finite beta are included in the analysis. The influence of the equilibrium parameters on the mode instability is carefully studied by employing the conventional alpha-Theta(0) equilibrium models. It is found that the behavior of the resistive wall mode (RWM) is rather sensitive to the reversal parameter F of RFPs. The effects of plasma rotation together with the viscosity and/or ion sound wave continuous spectrum damping can stabilize the RWM for certain positions of the wall relative to the plasma for both the low beta (or zero beta) and high beta plasmas. For typical RFP operating parameters, the rotation velocity required to stabilize the modes is in the range between the ion sound wave and Alfven wave velocities. This is larger than the natural rotation velocity in current RFPs, hence based on the above linear theory active feedback is needed for a long pulse RFP. A further nonlinear study is necessary. (C) 1999 American Institute of Physics. [S1070-664X(99)01210-0].