Kinetic damping of resistive wall mode in reversed field pinch

Abstract

The kinetic effects of thermal particles on the resistive wall mode (RWM) are studied in reversed field pinch (RFP) by adopting the toroidal hybrid stability code MARS-K (Liu et al 2008 Phys. Plasmas 15 112503) where the drift kinetic effects are included self-consistently. It is found that the transit ion resonance can provide ion acoustic Landau damping to stabilize the RWMs in high-beta plasmas. The trapped particles do not play a significant role in kinetic stabilization. The required critical flow rotation frequency is in the ion acoustic range which is much smaller than that predicted previously by fluid theory (Guo et al 1999 Phys. Plasmas 6 3868). The most unstable mode, having its rational surface closest to the plasma, can be stabilized for the wall near the plasma (e.g. n = 6 mode in RFX-mod) with the flow rotation in a few per cent of the Alfvén frequency. For other RWMs with different toroidal wave numbers n the stabilization conditions depend on the wall position and plasma βp. An analysis based on the potential energy components is carried out for physical understanding. The preliminary study on the effects of collisionality is also presented.