Modeling the generation of alpha-like RF fast ions by coupling a full wave solver to a Monte Carlo orbit follower

Future burning machines will have substantial alpha populations which are not present in existing experiments. These fast ions can resonate with Alfvén eigenmodes of tokamak magnetic equilibria and drive them unstable, which can increase alpha particle transport and lead to higher alpha losses to the wall, resulting in damage and reduced energy to the plasma. To create a fast ion population to mimic alpha particles, a high field side, traveling wave array (TWA) antenna couples a harmonic fast wave that damps on neutral beam ions and increases beam ions energies to those expected of fusion alpha particles. We also assess the impact the fast particle population has on the fast ion driven Alfven eigenmode activity. Our latest modeling approach brings together three codes: the full-wave RF code AORSA, a Monte-Carlo code MCGO, and Far3D, an Alfvén eigenmode modeling tool. We use MCGO in place of the CQL3D zero-orbit Fokker Planck code, used in previous iterations of this modeling effort, because finite orbit width effects will change where and how power is damped to the plasma for high harmonic energetic fast ions, changing the distribution function in both physical and velocity space. AORSA has been updated to ingest 4D R, Z, parallel and perpendicular distribution functions. Far3D is used to show how the presence of RF changes the excited mode spectra. Key metrics are proposed for making comparisons between the neutral beam/RF driven distributions generated here and alpha distributions in future burning power plants.