Characterization of Liquid Scintillator-Based CNES for Deuterium–Deuterium Neutron Emission Spectroscopy in the LHD

The compact neutron emission spectrometers (CNESs) based on conventional liquid (EJ-301) scintillation detectors were characterized in this work. The CNESs were employed for deuterium–deuterium neutron emission spectroscopy in the Large Helical Device (LHD). Prior to the installation, the EJ-301 scintillation detectors were characterized at the Fast Neutron Laboratory (FNL) of Tohoku University. In order to discriminate the neutron and
$\gamma $
-ray signals, the charge comparison method was used. The neutron energy spectrum was successfully unfolded from the measured recoil proton energy spectrum of the EJ-301 scintillation detector using the derivative unfolding technique. The detector’s energy resolution was examined. In the LHD, EJ-301-based CNESs with both tangential and perpendicular line-of-sight were employed for characterization. Furthermore, the characterization of the CNES was performed in the deuterium–deuterium experiment campaign. The operational capabilities of CNESs in the LHD were examined. Deuterium–deuterium neutron emission spectroscopy in various approaches of neutral beam (NB)-heated plasmas was conducted using CNES. Because of the high energy of the injected fast ions from tangential NB injection, an investigation of the Doppler effect on deuterium–deuterium neutron energy was conducted. The upper and lower shifted deuterium–deuterium neutron energies were observed when the fast ions moved toward and away from the tangential CNES, respectively. As expected, no notable energy shift was observed from fast ions injected by the perpendicular NB injection. Additionally, the 5-D orbit following code DELTA5D, which takes into account Larmor motion effects and the detector’s energy resolution, was utilized to compute the expected deuterium–deuterium neutron energy spectrum that would be measured by the CNES. There was a concurrence between the calculations and experimental results.