Resonant interaction of fast particles with neoclassical tearing modes

Cherenkov resonance between rotating neoclassical tearing mode (NTM) and energetic ions has been considered. Resonant interaction drives the current, which is in phase quadrature with the magnetic island and thus produces a toroidal torque accelerating island in the direction of the fast ion diamagnetic drift. This torque has been included in the coupled nonlinear first-order differential equations governing evolution of the NTM rotation frequency and amplitude. It has been shown that due to resonant interaction with energetic ions, this autonomous system exhibits Hopf bifurcation from the unstable stationary solution to the stable limit cycle describing nonlinear oscillations of the mode frequency and amplitude. Such behavior resembles the frequency jump events observed during NTM activity in ASDEX Upgrade [S. Guenter , Phys. Plasmas 7, 935 (2000)]. (C) 2001 American Institute of Physics.