Enhancement of radial transport of energetic ion by helically-trapped energetic-ion-driven resistive interchange mode in LHD

Deuterium experiment was initiated to achieve higher-temperature and higher-density plasmas in March 2017 in the Large Helical Device (LHD). The central ion temperature notably increases compared with that in hydrogen experiments. However, energetic particle modes called the helically-trapped energetic-ion-driven resistive interchange modes (EIC) are often excited by intensive perpendicular neutral beam injections on high ion-temperature discharges. The mode leads to significant decrease of the ion temperature or to limiting the sustainment of the high ion-temperature state. To understand the effect of EIC on the energetic ion confinement, the radial transport of energetic ions is studied by means of the vertical neutron camera newly installed on LHD. Decreases of line-integrated neutron emission profile in core channels are obtained. (author)