The commissioning of three different types of D-D neutron energy spectrometer has been performed in the Large Helical Device (LHD) to accelerate energetic-ion physics studies in a non-axisymmetric system. Because the LHD is equipped with negative-ion-source-based tangential neutral beam injectors (N-NBs) characterized by high energy up to 180∼190 keV, a significant Doppler shift of D-D neutron energy from 2.45 MeV is expected. Two different compact neutron energy spectrometers, i.e., a

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... nal liquid organic scintillator, designated as EJ-301, and a newly developed Cs 2 LiYCl 6 :Ce with 7 Li-enrichment called CLYC7, having tangential sightlines, have shown up-and/or down-shifted D-D neutron energy, as expected according to the direction of N-NB injection. In addition, with the aim of study on a perpendicular energetic ion tail, created by wave heating with ion cyclotron resonance frequency, a neutron energy spectrometer named the Time of Flight Enhanced Diagnostic (TOFED) is being developed. The TOFED is based on a time-of-flight technique and is characterized by highenergy-resolution and a high-counting-rate capability. Commissioning of the TOFED is now ongoing. Recent advances of neutron energy spectrometer development for LHD deuterium plasmas are described.