Calculation of DD and DT neutron contribution matrix for ITER vertical neutron camera detectors

• Published in: Fusion engineering and design 2021-12, Vol.173, p.112874, Article 112874
• Main Authors: Rodionov, R., Kumpilov, D., Nemtcev, G., Bertalot, L., Vysokih, J.
• Format: Article
• Language: English
• Subjects: Cameras; Collimators; Detector contribution matrix; Detectors; Diamonds; Fission; ITER; Mathematical analysis; MCNP; Neutron emission; Neutron flux; Neutron scattering; Neutrons; Rings (mathematics); Sensors; Vertical Neutron Camera
• ISSN: 0920-3796; 1873-7196
• DOI: 10.1016/j.fusengdes.2021.112874

•Detector contribution matrices were calculated for DD and DT neutrons using MCNP.•Monte Carlo calculations of contribution matrices allows to consider scattered neutrons.•Contribution matrix enables fast simulation of detector signals for different plasma configurations. ITER Vertical Neutron Camera (VNC) is a diagnostic intended to measure time- and space-resolved neutron emission profile in the poloidal plasma section. It is composed of the two fan-shaped collimating structures: lower (5 collimators) and upper (6 collimators). Every collimator contains 2 fission chambers and 2 diamond detectors. Axisymmetric plasma neutron source can be discretized as a set of square section rings. In this case, the count rate of a detector is a superposition of the count rates from every ring neutron source. The contribution matrix determines the contribution of each ring neutron source to the count rate of every detector. Usually, it can be calculated analytically. But in case of VNC background neutron flux in the detectors is significant and neutron scattering on tokamak structural materials must be considered. We have calculated the contribution matrices of the VNC detectors for both DT and DD neutrons using MCNP code. We used these matrices to calculate fission chamber count rates and neutron fluxes at detector locations for ITER reference DT neutron source (Tion=25 keV). The results agree with the values obtained by direct MCNP computations. Once calculated they allow fast simulation of detector signals for different plasma configurations.