Modelling of Neutron Markers for the COMPASS Upgrade Tokamak and Generation of Synthetic Neutron Spectra

In the future COMPASS Upgrade (Vondracek et al. in Fusion Eng Des 169:112490, https://doi.org/10.1016/j.fusengdes.2021.112490, 2021) tokamak (\(R_0 = 0.894\, \mathrm {m}\), \(B_t \sim 5\, \mathrm {T}\)), three distinct types of edge transport barrier are anticipated: ELMy H-mode, EDA H-mode and I-mode. The main auxiliary heating system used to access H-mode will be Neutral Beam Injection (NBI) power. The NBI will have a nominal injection energy of \(80\,\mathrm {keV}\) at a maximum injection radius \(R_{\mathrm {tan}} = 0.6\, \mathrm {m}\). A significant neutron yield will occur from the interaction of the beam with the plasma background. Using our orbit-following code EBdyna (Jaulmes et al. in Nucl Fusion 61, 046012, https://doi.org/10.1088/1741-4326/abd41b, 2021), we calculate the trajectories of the NBI ions during the complete thermalization process, calculate the amount of NBI ions losses and evaluate the neutron rate in steady state from the beam–plasma and beam–beam interaction. Combining it with the thermal yield, we can derive detailed synthetic spectrogram of the energy distribution of the neutrons. The markers can be further used to provide synthetic neutron spectrometer diagnostics data. Due to the reduction of the simulated neutron count seen by the detectors when the peaking of the neutron source is lower, we anticipate the need for absolute-calibration in order to recover quantitative results.