Magnetohydrodynamic instability excited by interplay between a resistive wall mode and stable ideal magnetohydrodynamic modes in rotating tokamak plasmas

Aiba, Nobuyuki; Hirota, Makoto*

A mechanism exciting magnetohydrodynamic (MHD) instabilities in rotating tokamak plasmas is found numerically for the first time. This mechanism is the interplay between a resistive wall mode (RWM) and a stable MHD mode. When the plasma has a stable discrete eigenmode, a reversed shear Alfvn eigenmode (RSAE) for example, a MHD mode is destabilized when plasma equilibrium rotation frequency is similar to the frequency of this stable eigenmode in a static equilibrium. This destabilization is also observed even when the eigenmode couples with Alfvn continua. This result suggests that for steady state high beta tokamaks, like DEMO, it is necessary to shape the safety factor profile in such a way that no stable eigenmode exists in the band of rotation frequency. With a dispersion relation, it was shown explicitly that plasma rotation switches the unstable mode from the RWM to the ideal MHD mode destabilized by wall resistivity.