7th Asia-Pacific Conference on Plasma Physics, 12-17 Nov, 2023 at Port Messe Nagoya

Progress in the development of a compact D-T neutron spectrometer based on asingle-crystal chemical vapor deposition diamond stack for fusion plasma
diagnostic
L. Y. Liao1, K. Ogawa1, 2, M. Isobe1, 2, S. Sangaroon3 and Y. Kawamoto1, 2
1
The Graduate University for Advanced Studies, SOKENDAI
2
National Institute for Fusion Science, National Institutes of Natural Sciences3
Department of Physics, Faculty of Science, Mahasarakham University
e-mail (speaker): liao.longyong@nifs.ac.jp

In a future D-T fusion reactor, neutron diagnostic will be
one of the key diagnostics because the neutron has
information for the birth profile of alpha particles, fuelion density ratio, and fuel ion temperature if the plasma
is Maxwellian. Diamond detectors are very promising
candidates for neutron diagnostics in the harsh radiation
environment of a fusion reactor because of their highradiation tolerance and compactness. The neutron
diagnostic based on a natural diamond was developed
and has been used since the 1990s for 14 MeV D-T
neutron measurements in large Tokamaks, such as TFTR
[1], JET [2], and JT-60U [3]. Recently, with thedevelopment of the diamond produced by chemical
vapor deposition, high-quality artificial diamond detector
becomes available at relatively low cost.
We are developing a novel compact D-T neutron
spectrometer based on a single-crystal chemical vapor
deposition (s-CVD) diamond stack (B14 diamondtelescope detector, CIVIDEC Instrumentation GmbH).
Figure 1 shows the measurement principle of a compact
neutron spectrometer (a) and the parameters of thediamond telescope detector (b). A neutron to proton
converter was installed in front of the detector. The
detector consists of one thin and two thick s-CVD
diamond sensors. This spectrometer was designed for thedetection of 3 MeV to 17 MeV neutrons. The incident
fast neutron creates a recoiled proton inside the converter.
The forward scattering recoiled proton deposits theenergy into the s-CVD diamond sensors. The pulse

signals of three sensors are acquired individually. The
neutron spectrum is obtained by coincidence analysis inwhich the gamma background can be rejected. Here, thethickness of the converter should be chosen according tothe neutron flux and energy resolution requirement. Anincrease in the thickness of the converter enhances thedetection efficiency but causes low energy resolution
because the deposition energy of the proton inside theconverter is unmeasurable.
We surveyed the effect of the converter thickness onenergy resolution and detection efficiency using 0.025 to
2.3 mm thick polyethylene films. We first tested thespectrometer with a 252Cf neutron source. Then, the D-D,D-T, and D-Li experiments were performed using theaccelerator-based neutron sources OKTAVIAN in Osaka
University and the Fast Neutron Laboratory in Tohoku
University. The detail of the compact D-T neutron
spectrometer as well as the effect of polyethylene
converter thickness on energy resolution and detection
efficiency will be presented.
References[1] A. V. Krasilnikov et al, Rev. Sci. Instrum. 68,553-556 (1997).
[2] A. V. Krasilnikov et al, Nucl. Instrum. Methods Phys.
Res. A 476, 500-505 (2002).
[3] M. Isobe et al, Fusion Eng. Des. 34-35, 573-576(1997).

Figure 1. (a) The measurement principle of a compact neutron spectrometer. (b) The parameters of the diamondtelescope detector.