Abstract: Gyrokinetic simulations are conducted to investigate the influence of the radial electric field (Er) on energetic particle (EP) transport in the Large Helical Device (LHD). The results reveal that both the sign and magnitude of Er significantly impact helically trapped ions, even when their kinetic energies greatly exceed the electrostatic potential introduced by Er. Specifically, Er alters particle orbit topologies, either opening new loss channels for EPs and thereby reducing confinement, or suppressing these loss channels and enhancing confinement, depending on the Er profiles. These findings underscore the potential role of Er in modulating EP dynamics and the possibility of manipulating the electric field by fast ions to improve confinement of alpha particles and thermal plasmas in the stellarator reactors.