Nonlinear evolution of the alpha-particle-driven toroidicity-induced Alfvén eigenmode

A fast and efficient numerical algorithm using energy conservation is developed to study the interaction of high-energy particles with a toroidicity-induced Alfvén eigenmode (TAE). A Hamiltonian guiding center code is used to simulate the alpha particle motion and a nonlinear δf scheme is employed to calculate the wave-particle energy exchange. The code is benchmarked using the bump-on-tail problem and simulation results agree with analytical estimates. For a single TAE mode, the particle radial excursion is much less than the spacing between the resonances produced by the poloidal harmonics for International Thermonuclear Experimental Reactor parameters. Resonant particles that lose their energy to the wave can become trapped poloidally, but transfer to a loss orbit through this mechanism does not occur. Modification of the particle distribution leading to mode saturation is observed.