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

Abstract

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 6 Li 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 6 Li 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.

Thermal Neutron Measurement Capability of a Single Crystal CVD Diamond Detector near the Reactor Core Region of UTR-KINKI

“…On the other hand, those generated by gamma-ray irradiation distribute in the entire bulk of the SCD by electron scattering. As a result, rectangular and triangular shaped pulses can be obtained by the energetic charged particles and gamma-ray irradiation, respectively [10,11,18].…”

“…For example, a twostep like pulse is usually obtained when a fast neutron interacts in the bulk of the SCD [19]. This two-step like shaped pulse can be misjudged as a triangular shaped pulse in the measurement using a conventional data acquisition system with the previous PSD method [10]. On the other hand, an event where fast neutrons hit on the surface of the SCD results in a rectangular shape, as in the case of energetic charged particles.…”

“…The monitoring of fast neutrons using the SDD is proposed for the control of burning plasma. Indeed, there are some reports where the neutron yield from the fusion plasma was monitored by the SDD [3][4][5][6][7][8][9][10].…”

Evaluation of tritium production rate in a blanket mock-up using a compact fusion neutron source

“…Transport of charged particles in the SDD was simulated by the PHITS code [29] with the intranuclear cascade model [30] and the JENDL 4.0 nuclear data [31]. The geometry for the PHITS calculations is composed of the 6 LiF film, the housing, lid, diamond, and air (in the window and outer region of the SDD) based on the model in the previous study [22]. In the PHITS calculations, neutron energy spectra obtained by MCNP were set as source particles to track neutrons and charged particles and to evaluate energy deposition E d by each particle onto the diamond.…”

Thermal neutron measurement by single crystal CVD diamond detector applied with the pulse shape discrimination during deuterium plasma experiment in LHD

“…In the Large Helical Device (LHD), which is one of the world's largest superconducting "stellarator" type fusion machines, D-D plasma experiment initiated in March 2017 [17][18][19]. One single crystal CVD diamond detector (SDD) was installed and used in the LHD torus hall during the 2 nd campaign of the D-D experiment with the goal to measure and characterize the neutron flux [20]. This SDD was made with a SCD with the thickness of 140 μm, and covered by a 1.9 μm-thick 6 LiF foil.…”