Comparisons of Energetic Particle Confinement in Stellarator Configurations*

Recent progress in stellarator optimization has identified configurations with very good energetic particle confinement. These configurations are typically found by optimizing either quasisymmetry, neoclassical metrics such as ε_eff and Γ_c, or both. However comparisons across configurations have typically been difficult to obtain due to differences in device size and field strength. In this poster, we present alpha particle confinement results from 9 stellarator configurations of different types, including quasihelically symmetric, quasiaxisymmetric, quasi-isodynamic, and σ-optimized configurations. Results for calculations with and without collisions are presented. Analysis of the metrics shows that good alpha particle confinement is highly corellated with the Γ_c metric, while the correlation with quasisymmetry is weaker. When collisions are included, configurations with losses near the trapped boundary perform relatively worse compared to configurations with deeply trapped losses. This suggests possibilities of optimizing for specific classes of collisionless particle losses.