Investigating the relationship between the radial electric field and neutral beam injected energetic particles in LHD

Understanding energetic particle (EP) transport is crucial for optimizing stellarator performance and enhancing fusion efficiency. In this research, we utilize the gyrokinetic toroidal code (GTC) to perform neoclassical simulations of EP transport in the Large Helical Device (LHD) to investigate the relationship between the ambipolar radial electric field (Er) and neutral beam injected (NBI) EP dynamics. To capture the realistic behavior of EPs, we use as input the slowing-down distribution function of fast ions obtained from GNET simulations. A positive Er is found to reinforce the poloidal precession velocity of trapped particles, reducing radial transport and improving confinement. The Er calculated from the ambipolar fluxes of ions and electrons in GTC is compared with experimental data.