Energetic ion anisotropy was observed by tangential sightline compact neutron energy spectrometers (CNESs) in tangential neutral beam heated deuterium plasmas in Large Helical Device. Significant upper and lower energy shifts in D–D neutron energy from 2.45 MeV were measured according to the beam ion injection directions and CNES sightline using a conventional liquid scintillation detector with the unfolding technique and a novel Cs2LiYCl6:Ce with a 7Li-enrichment (CLYC7) scintillation detector without unfolding. The observed neutron energy spectrum was compared with that predicted by a numerical simulation based on orbit following models. Numerical simulation revealed that the Doppler shift in D–D neutron energy results from energetic ion anisotropy.
This paper reports the observation of energetic ion anisotropy in the Large Helical Device using neutron diagnostics. Significant energy shifts in the D-D neutron energy were measured, indicating the presence of directional energetic ions. Numerical simulations confirmed that the Doppler shift in the neutron energy is caused by this energetic ion anisotropy.