# Fast Ion Speed Diffusion Effect on Distributions of Fusion Neutrons
## 4 Conclusions  
Calculations of distributions of fusion neutrons in the presence of suprathermal deuterium and tritium nuclei originating form a monoenergetic source in Maxwellian plasma have been performed. The role of the speed diffusion effect in the fuel nuclei velocity space in the formation of energy distributions of products of \({}^{3}\)H(\({}^{2}\)H,n)\({}^{4}\)He and \({}^{2}\)H(\({}^{2}\)H,n)\({}^{3}\)He fusion reactions has been studied. High-energy tails of distributions of fast ions velocities in the regions below and above the beam injection velocity influence the energetic and angular distributions of nuclear fusion products.  
The effect of the fast ion speed diffusion on the obtained neutron spectra is noticeable; however, it does not significantly modify the qualitative behavior of the spectra and such general parameters as full width at half maximum. Thus, the use of simplified analytical models for the ion distribution functions is reasonably justified when the knowledge of \"fine structure\" of neutron spectra is not required.  
Advanced plasma diagnostics, such as high-resolution neutral particle analysis combined with high-resolution neutron spectrometry, may be used for experimental validation of the mathematical models described herein. Recent progress on the development of active charge exchange diagnostics of fast ion distributions and neutron spectroscopic diagnostics on Globus-M2 spherical tokamak [44] were reported in [45] and [46], respectively. An  
Figure 7: Total energy spectra of neutrons, integrated over the entire range of emission angles, calculated with speed diffusion effect taken into account (green) and without accounting for the speed diffusion effect (dark blue). (**a**) For \({}^{3}\)H(\({}^{2}\)H,n)\({}^{4}\)He reactions corresponding to velocity distributions of deuterons and tritons shown in Figure 1; (**b**) for \({}^{2}\)H(\({}^{2}\)H,n)\({}^{3}\)He reactions corresponding to velocity distributions of deuterons shown in Figure 2.  
excellent powerful set of neutron diagnostics operating on the Large Helical Device (LHD) in combination with advanced diagnostics of energetic ions was described in [47]. Measurements of anisotropic distributions of fusion neutrons in experiments with deuterium plasma heated by neutral beam injection on LHD were reported in [48]. Neutron emission spectroscopy on Joint European Torus (JET) was overviewed in [49]. Prospects of various neutron diagnostics foreseen for ITER, including neutron flux monitors and spectrometers, were described in [50].  
The results may be applied for simulations of energetic and angular distributions of neutrons and charged nuclear fusion products in magnetically confined plasma in the framework of the activities on the development of fusion energy reactors and fusion neutron sources employing beam-plasma interactions.  
The research was funded by the Ministry of Science and Higher Education of the Russian Federation under the strategic academic leadership program \"Priority 2030\" (Agreement 075-15-2021-1333 dated 30.09.2021) and partially supported in the framework of the IAEA Coordinated Research Project under contract No. 22765.  
Not applicable.  
The results were obtained using computational resources of Peter the Great Saint Petersburg Polytechnic University's Supercomputing Center (scc.spbstu.ru).  
The author declares no conflict of interest.