Stability of the global Alfvén eigenmode in the presence of fusion alpha particles in an ignited tokamak plasma

Abstract

The stability of global Alfvén eigenmodes is investigated in the presence of super-Alfvénic energetic particles, such as fusion-product alpha particles in an ignited deuterium–tritium tokamak plasma. Alpha particles tend to destabilize these modes when ω*α>ωA, where ωA is the shear-Alfvén modal frequency and ω*α is the alpha particle diamagnetic drift frequency. This destabilization due to alpha particles is found to be significantly enhanced when the alpha particles are modeled with a slowing-down distribution function rather than with a Maxwellian distribution. However, previously neglected electron damping due to the magnetic curvature drift is found to be comparable in magnitude to the destabilizing alpha particle term. Furthermore, the effects of toroidicity are also found to be stabilizing, since the intrinsic toroidicity induces poloidal mode coupling, which enhances the parallel electron damping from the sideband shear-Alfvén Landau resonance. In particular, for typical ignition tokamak parameters, global Alfvén eigenmodes are found to be completely stabilized by either the electron damping that enters through the magnetic curvature drift or the damping introduced by finite toroidicity.