Wall mode stabilization at slow plasma rotation

Unstable pressure-driven external kink modes, which become slowly growing resistive wall modes (RWMs) in the presence of a resistive wall, can lead to tokamak plasma disruptions at high beta. It has been shown that RWMs are stabilized by fast plasma rotation (about 1-2\% of the Alfv\'en frequency) in experiments. Conventional theories attribute the RWM suppression to the dissipation induced by the resonances between plasma rotation and ion bounce/transit or shear Alfv\'en frequencies [1]. In those theories, the kinetic effects associated with the plasma diamagnetic frequencies and trapped-particle precession drift frequencies are neglected. It has been observed in recent experiments [2,3] that the RWM suppression also occurs at very slow plasma rotation (about 0.3\% of the Alfv\'en frequency), where the conventional dissipation is too small to fully suppress the RWMs. Here it is shown, that the trapped-particle kinetic contribution associated with the precession motion [4] is large enough to stabilize the RWM in DIII-D at low rotation. Work supported by the US-DoE OFES. \noindent [1] A. Bondeson and M. S. Chu, Physics of Plasmas, {\bf 3},3013 (1996). [2] H. Reimerdes {\it et al.}, Physical Review Letters, {\bf 98},055001 (2007). [3] M. Takechi {\it et al.}, Physical Review Letters, {\bf 98},055002 (2007). [4] B. Hu and R. Betti, Physical Review Letters, {\bf 93},105002 (2004).