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Diamond-based detectors have gained significant attention in fusion neutron diagnostics owing to their outstanding radiation hardness, sub-nanosecond timing response, and capability for energy-resolved measurements [1,2]. In this study, neutron spectrometry experiments were conducted at the KSTAR tokamak using two geometrically distinct single-crystal diamond detector systems. Time-resolved measurements of 2.45 MeV D–D fusion neutrons were performed during neutral beam injection (NBI) plasmas, with neutron emission rates reaching up to 10¹¹ n/s. The measured pulse-height spectra exhibited distinct signatures of the ¹²C(n,α)⁹Be reaction; the planar-type detector provided superior intrinsic energy resolution, whereas the axial-type detector achieved higher detection efficiency and operational robustness under high-flux conditions (>10⁸ n/cm²/s), making it more suitable for high-rate fusion environments [1,2]. A strong correlation with micro-fission chamber and ³He counter data verified the accuracy of neutron yield determination [3,4]. Owing to the inherently low gamma-ray sensitivity of diamond sensors, reliable neutron measurements were achieved even in mixed neutron–gamma radiation fields, highlighting their practical utility in realistic fusion reactor environments [2]. While the present work focuses on point-detection spectrometry, the demonstrated fast timing capability, high count-rate tolerance, compact form factor, and radiation hardness indicate that diamond detectors constitute a promising sensor platform for future fast-neutron imaging and tomographic diagnostics in fusion devices [1,5]. These results confirm the reliability of diamond detectors for real-time fusion neutron spectrometry and support their scalability for high-flux diagnostic applications foreseen in devices such as K-DEMO and ITER.
[1] C. Weiss et al., Fusion neutron diagnostics with CVD diamond detectors, Nuclear Instruments and Methods A (2024).
[2] C. Cazzaniga et al., Single-crystal diamond detector measurements of DD and DT fusion plasmas, Rev. Sci. Instrum. 85, 043506 (2014).
[3] Y. Lee et al., Diamond fast-neutron detector applied to the KSTAR tokamak, Fusion Engineering and Design 153 (2020) 111452.
[4] Y. Lee et al., D-D Fusion Neutron Spectrometer in the KSTAR Tokamak, Transactions of the Korean Nuclear Society Spring Meeting (2025).
[5] D. Rigamonti et al., Single-crystal diamond-based neutron diagnostics for fusion applications, Nucl. Fusion, 2024.
This research was supported by R&D Program of "High Performance Tokamak Plasma Research & Development (KFE-EN2601)” through the Korea Institute of Fusion Energy (KFE) funded by the Government funds, Republic of Korea.