Kinetic Effects of Energetic Particles on Nonlinear Resistive MHD Stability

Kinetic effects of energetic particles can play a crucial role in the stability of the 2/1 tearing mode in tokamaks (JET, JT-60U, and DIII-D), where the fraction of energetic particle $\beta _{frac}=\beta _{h}$/$\beta _{ }$is high. Using model equilibria based on experimental reconstructions, it has been shown that energetic particles have significant damping and stabilizing effects at experimentally relevant $\beta _{N}{\rm s}{\rm g}\beta _{frac}$, and $S$, and weaker damping and stabilizing effects in the ideal unstable regime, and excite a real frequency of the 2/1 mode [1,2]. Initial nonlinear and two-fluid effects are now investigated. A qualitative extrapolation of these results is discussed for what to expect from energetic particle effects on resistive MHD modes in ITER.\\[4pt] [1] R. Takahashi, \textit{et al}., Phys. Rev. Lett. 102, 135001 (2009).\\[0pt] [2] R. Takahashi, \textit{et al}., Nucl. Fusion 49, 065032 (2009).