Energetic particle loss under the effects of the radial electric field in LHD

Abstract The impact of the radial electric field ( E r ) on the confinement of energetic particles (EPs) in the Large Helical Device is studied through gyrokinetic simulation. Particle orbits are characterized as passing, helically trapped, and barely trapped. E r has little effect on passing particles. A positive E r is found to improve the confinement properties of trapped particles by increasing their precession rate, thereby reducing radial drift over a bounce motion. A negative E r is found to do the opposite. E r can induce particles to change orbit topology. The effects of an experimental E r profile are discussed. Overall, positive E r is found to improve while negative E r is found to degrade confinement of energetic particles. Furthermore, the lost energetic particles originate from localized regions of phase space. Knowledge of which can be utilized to induce radial current to control E r by injecting neutral beams into these regions.