Thermal neutron flux evaluation by a single crystal CVD diamond detector in LHD deuterium experiment

A single crystal CVD diamond detector (SDD) was installed in the torus hall of the Large Helical Device (LHD) to measure neutron during deuterium plasma operation. The LiF foil with 95.62% of 6Li isotope enrichment pasted on the detector was used as the thermal neutron convertor. The energetic ions of 2.0 MeV alpha and 2.7 MeV triton particles generated by the nuclear reaction of neutron with 6Li in LiF foil. Then, energetic ions deposited the energy into diamond, producing a signals in SDD. SDD were exposed to the neutron field in the torus hall of the LHD during the 2nd campaign of the deuterium experiment. The total charge in SDD during one plasma shot in LHD was linearly propotional to the neutron yield over 4 orders of magnitude. The energetic alpha and triton were separately measured by SDD with LiF with the thickness of 1.9 μm, although SDD with LiF with the thickness of 350 μm showed a broadened peak due to the large energy loss of energetic particles generated in the bulk of LiF. The modeling with MCNP and PHITS codes well interpreted the pulse height spectra for SDD with LiF with different thicknesses