Energetic particle loss mechanisms in reactor-scale equilibria close to quasisymmetry

Collisionless physics primarily determines the transport of fusion-born alpha particles in 3D equilibria. Several transport mechanisms have been implicated in stellarator configurations, including stochastic diffusion due to class transitions, ripple trapping, and banana drift-convection orbits. Given the guiding center evolution in a set of six quasihelical and quasiaxisymmetric equilibria, we perform a classification of trapping states and transport mechanisms. In addition to banana drift convection and ripple transport, diffusive banana tip motion associated with the non-conservation of the parallel adiabatic invariant is substantial among prompt losses, especially in quasiaxisymmetric equilibria. Furthermore, many lost trajectories undergo transitions between trapping classes on longer time scales, either with periodic or irregular behavior. We discuss possible optimization strategies for each of the relevant transport mechanisms and perform a comparison between classified guiding center losses and recently-developed metrics for banana drift convection transport. Equilibrium characteristics responsible for distinctions in transport are discussed. Quasihelical configurations are found to have natural protection against both ripple trapping and diffusive banana tip motion.