Investigating the effects of the Neutral Beam induced Radial Electric Field on Energetic Particle Transport in LHD Stellarator*

Stellarators may face challenges in controlling the transport of energetic particles (EPs) within their magnetic configurations. Understanding 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 influence of the ambipolar electric field on 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. We then perform simulations in GTC starting from the initial beam deposition to obtain the slowing down distribution. These results are compared with preliminary results from an experiment on LHD. Furthermore, fast ions can also affect the ambipolar radial electric fields in the stellarator. More LHD experiments have recently been carried out to study the interaction between fast ions and radial electric fields. Preliminary analysis of these experiments will also be reported.