Development of 2.5 MeV neutron spectrometer toward deuterium plasma diagnostics in LHD

Tomita, Hideki*; Iwai, Haruki*; Iguchi, Tetsuo*; Kawarabayashi, Jun*; Isobe, Mitsutaka*; Konno, Chikara  

Neutron spectrometer based on coincident counting of associated particles has been developed for deuterium plasma diagnostics on Large Helical Device (LHD) at National Institute for Fusion Science. Efficient detection of 2.5 MeV neutron with high energy resolution would achievable by coincident detection of a scattered neutron and a recoiled proton associated to a elastic scattering of incident neutron in a plastic scintillator as a radiator. Calculated neutron spectra from deuterium plasma heated by neutral beam injection indicate that the energy resolution of less than 7% is required for the spectrometer to evaluate energetic deuterium confinement. By using a prototype of the proposed spectrometer, the energy resolution of 6.3% and the detection efficiency of 3.310 counts/neutron were experimentally demonstrated for 2.5 MeV mono-energetic neutron, respectively.