Observation of Helically-Trapped Energetic Particle Transport Induced by Energetic-Ion-Driven Resistive Interchange Mode using Imaging Neutral Particle Analyzer in Large Helical Device

       Energetic-ion-driven resistive interchange mode (EIC) is one of magnetohydrodynamic (MHD) instabilities often observed in the Large Helical Device (LHD). EIC has been excited by helically-trapped energetic particles (EPs) injected by positive-source neutral beam (P-NB) in high ion-temperature discharges in Large Helical Device (LHD) [1], significantly enhancing radial transport and causing the loss of EPs [2, 3]. Understanding these instabilities is critical for improving EP confinement. In this work, we investigate the transport of helically trapped EPs induced by EIC in LHD using a newly developed Imaging Neutral Particle Analyzer (INPA) [4]. The INPA employs a magnetic spectrometer utilizing a ZnS:Ag scintillator to detect charge-exchanged energetic neutral particles escaping from the plasma. The system uses a 90 nm thick carbon foil to ionize these energetic neutrals, which are subsequently deflected by the local magnetic field toward the scintillator for detection. This setup provides spatially and energy-resolved measurements of energetic neutral flux with time resolution, offering detailed insights into EPs behavior during MHD instabilities. In this experiment, negative-source-based NBs (N-NBs) and P-NBs were injected with energies of 160–180 keV and ~ 40 keV, respectively. The total INPA intensity decreases following EIC bursts, indicating substantial energetic-particle transport. The detailed analysis of the energy and radial transport will be presented.