Neutron spectroscopy measurements of 14 MeV neutrons at unprecedented energy resolution and implications for deuterium–tritium fusion plasma diagnostics

Abstract

An accurate calibration of the JET neutron diagnostics with a 14 MeV neutron generator was performed in the first half of 2017 in order to provide a reliable measurement of the fusion power during the next JET deuterium-tritium (DT) campaign. In order to meet the target accuracy, the chosen neutron generator has been fully characterized at the Neutron Metrology Laboratory of the National Physical Laboratory (NPL), Teddington, United Kingdom. The present paper describes the measurements of the neutron energy spectra obtained using a highresolution single-crystal diamond detector (SCD). The measurements, together with a new neutron source routine 'ad hoc' developed for the MCNP code, allowed the complex features of the neutron energy spectra resulting from the mixed D/T beam ions interacting with the T/D target nuclei to be resolved for the first time. From the spectral analysis a quantitative estimation of the beam ion composition has been made. The unprecedented intrinsic energy resolution (<1% full width at half maximum (FWHM) at 14 MeV) of diamond detectors opens up new prospects for diagnosing DT plasmas, such as, for instance, the possibility to study non-classical slowing down of the beam ions by neutron spectroscopy on ITER.

Detector Response to D-D Neutrons and Stability Measurements with 4H Silicon Carbide Detectors

“…Solid State Detectors (SSDs) represent a recent option for neutron detection in high-flux applications, since they combine a good pulse height energy resolution and fast response time while having compact dimensions [ 1 , 2 ]. The SSD scene is currently dominated by diamond detectors, which, for instance, are currently installed at the JET tokamak [ 3 ] as neutron spectrometers [ 2 , 4 ] and at the ChipIr beamline at ISIS [ 5 ] as beam monitors [ 6 , 7 ]. However, the development of large high-power tokamaks (such as ITER [ 8 ]) requires neutron detectors to be installed closer to the plasma and, therefore, to be able to sustain the high temperature and neutron flux of such an environment.…”

Detailed reproduction of the neutron emission from the compact DT neutron generator used as an in-situ 14 MeV calibration neutron source at JET

“…A high resolution measurement of the neutron emission spectrum directly in front of the NG ( Figure 1) was performed to determine relative intensities of different DT source components. This spectrometer position was chosen due to the widest spread of the DT neutron emission peaks in such positions and thus the combination of the state of the art neutron spectrometer based on the diamond detector and simulations could be used to provide insight into the relative intensities of different DT neutron source components [6].…”

“…The relative intensity of all expected DT source components in the NG was determined by fitting individual detector responses for each of the components to the measurement ( Figure 3) [6]. The response function of the detector was applied to the calculated spectra for realistic fitting and the correlation of T(d, n) 4 He and D(t, n) 4 He were taken into account to decrease the amount of independent variables.…”

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

“…A single crystal diamond (SCD) is an attractive material as a fast neutron detector [1,2]. Therefore, the application of a single crystal diamond detector (SDD) has been of interest in fusion reactor development because of fast neutrons generated by D (deuterium) -T (tritium) fusion reactions.…”