Synergistic effects of turbulence induced viscosity and plasma flow on resistive wall mode instability

A new damping model on the resistive wall mode (RWM) instability is studied, via the turbulence induced plasma viscosity (in short, turbulent viscosity). In a cylindrical plasma, the synergistic effect on suppressing the RWM is investigated between this new damping mechanism and the plasma flow. An eigenmode formulation is derived based on magneto-hydrodynamic (MHD) theory, where the momentum equation is extended by including the turbulent viscosity term with a proportionality coefficient χ. Numerical results show that, in the absence of plasma flow, increasing χ decreases the RWM growth rate but does not fully stabilize the mode. However, in the presence of sufficiently fast plasma flow, turbulent viscosity can lead to full suppression of the RWM, when χ exceeds a critical value. Similarly, at a given χ value, the plasma flow can fully suppress the mode when the flow velocity exceeds a threshold value. In particular, turbulent viscosity significantly reduces the threshold value of the flow velocity required for full stabilization of the RWM. (paper)