Observation of significant Doppler shift in deuterium-deuterium neutron energy caused by neutral beam injection in the large helical device

Abstract

The compact neutron emission spectrometer (CNES) having a tangential sightline was installed to observe a significant Doppler shift of the neutron energy due to the high-energy tangential neutral beam (NB) injections in the Large Helical Device (LHD) for understanding of the energy distribution of fast-ion. The CNES is based on a 1-inch diameter and 1-inch height EJ301 liquid scintillator coupled with a conventional 1-inch photomultiplier tube. The histogram of the integrated pulse signal (Qtotal) during different NBs heating phases measured by the CNES shows that the edge of Qtotal changes depending on NB directions. Using the simple derivative unfolding technique, the neutron energy spectra were unfolded from the measured Qtotal histogram. Peaks of the neutron energy shift to 2.0 MeV, 2.42 MeV, and 3.0 MeV according to the injection direction of NBs. The obtained neutron energy is almost consistent with the virgin deuterium-deuterium neutron energy evaluated by the simple two-body kinematics considering the sightline of CNES, NB injection angle, and NB injection energy.

Observation of energetic ion anisotropy using neutron diagnostics in the Large Helical Device

“…gain shift due to the high anode current caused by high pulse counting rate should be avoided obtaining the neutron energy spectrum. In this discharge, the detectors were operated with low pulse counting rate 20 kcps for EJ-301 detector and 5 kcps for CLYC7 detector, which is one-tenth of the operational limit of CNES [81,82].…”

“…Because the liquid scintillation detector measures the proton energy recoiled by a fast neutron, unfolding is necessary for obtaining the neutron energy spectrum. The energy calibration of the detector was performed using a deuterium-deuterium reaction in the Fast Neutron Laboratory at Tohoku University [82]. We applied the derivative unfolding method to obtain the neutron energy spectrum.…”

Fusion product diagnostics based on commercially available chemical vapor deposition diamond detector in large helical device

“…Energetic particle confinement research, e.g., energetic particle confinement in magnetohydrodynamic quiescent plasmas [51][52][53], visualization of energetic particle transport [54][55][56][57][58][59], and demonstration of MeV ion confinement [60,61], has progressed [62,63]. Recently the beam ion energy spectrum has been studied using D-D neutron energy spectrometers [64][65][66][67][68]. Understanding of beam ion confinement will progress by measurement of the energy spectrum of charged particles produced by D-D reactions, i.e., tritons, protons, and 3 He, by D-T reactions, i.e., alpha particles, and by p-11 B reactions, i.e., alpha particles, because their energy has information on beam or MeV ion energies.…”

Gamma ray diagnostics for high time resolution measurement in large helical device

“…The relationship is different in tangential negative ion source and perpendicular positive ion source phases. The difference could potentially cause by the difference in neutron energy or neutron anisotropy [62][63][64][65]. The limitation of the pulse count rate of the LaBr 3 :Ce detector was approximately 200 kcps, where 𝑆 𝑛 was below 10 13 n/s.…”