Self-suppression of double tearing modes via Alfven resonance in rotating tokamak plasmas

Reversed magnetic shear configuration, a key method for improving plasma confinement in advanced tokamaks, is prone to exciting double tearing modes (DTMs) that can severely degrade the plasma confinement. In this letter, we reveal a new mechanism of suppressing the DTM instability due to the self-induced Alfven resonance in rotating tokamak plasmas. The linear growth rate is reduced from similar to S-Hp(-1/3) of the fast DTM regime to similar to S-Hp(-3/5) of the slow single tearing mode regime, where S-Hp is magnetic Reynolds number. Instead of generating magnetic islands at the inner rational surface that can greatly enhance plasma transport in the core region, the formation of current sheets at resonance layers not only prevents the fast nonlinear DTM reconnection phase but also contributes to plasma heating. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3586258]