Orbit-based analysis of resonant excitations of Alfvn waves in tokamaks

Bierwage, A.; Shinohara, Koji

The resonant interactions between shear Alfvn waves and resonant fast ions are analyzed numerically in realistic geometry and with a realistic particle distribution for a JT-60U plasma driven by two 400 keV N-NBs. In order to deal with the large magnetic drifts of the fast ions, a new orbit-based resonance analysis (ORA) method is developed and applied. The ORA method uses mappings that allows us to unify resonance conditions for trapped and passing particles, determine which harmonics are driven, and which orders of the resonance are involved. After analyzing the resonance conditions, the effects of wave-particle trapping, kinetic compression and linear resonance overlap are examined. Finally, we discuss the implications for frequency chirping, convective amplification, the long-time evolution of the system in the presence of a fast ion source, and for the interpretation of experimental observations.