Alfvén Instabilities Excited by Energetic Particles in a Parameter Regime Similar to EAST Operation

The kinetic excitation of ideal magnetohydrodynamic (MHD) Alfv´ en instabilities is investigated for operations at the EAST tokamak. The instabilities include α-induced toroidal Alfvén eigenmodes (αTAE; here, α = −q ² Rdβ/dr, with q being the safety factor, β the ra tio between the plasma and magnetic pressures, R the major radius, and r the minor radius), toroidicity-induced Alfv´ en eigenmodes (TAE), and the energetic particle continuum mode (EPM). The αTAE, trapped by α-induced potential wells along the magnetic field line, can be readily destabilized by energetic particles due to negligible continuum damping via wave energy tunnel- ing. It is shown for the geometry and the parameters similar to those of the EAST equilibrium that αTAE is different not only from the EPM by the potential-well determined frequency, but also from the TAE by the broad frequency spectrum outside the toroidal frequency gap.