2018 年 13 巻 p. 3402121
The deuterium plasma experiments have been conducted since March 2017 on the Large Helical Device. The neutron yield per shot has reached up to 7 × 1014 and 3.5 × 1015 in the first phase where NBI #1, 2, and 3 used hydrogen and NBI #4 and 5 used deuterium, and in full D-D phase, respectively. For the triton burnup study in this campaign, the neutron activation system (NAS) has been used to measure 14 MeV neutrons and 2.45 MeV neutrons. The triton burnup ratio of 0∼0.34% are obtained by the NAS measurement. Triton burnup ratio increases with electron density when line-averaged electron density is below about 2.5 × 1019 m−3, and decreases with electron density above 2.5 × 1019 m−3. Meanwhile, the triton burnup ratio decreases as the magnetic axis positions shift outward, which can likely be explained by the orbit of helically trapped energetic tritons. In addition to the NAS measurement, the phenomenon of the 14MeV neutron emission lagging at the 2.45 MeV neutrons emission has been observed by the time evolution measurement with scintillating-fiber detectors and neutron flux monitor.
