## 5 Discussion of Results  
In Figure 2, we can see that for the D + T beam, with an increasing fraction of tritium \(f_{core}T\), the efficiency of neutron generation became higher. In the case of the D + T beam, the \begin{table}
\begin{tabular}{c c} \hline \hline
**Parameter** & **Value** \\ \hline Major plasma radius \(R\) (m) & 0.5 \\ Ratio \(R/a\) & 1.66 \\ Elongation \(\kappa_{elong}\) & 2.75 \\ Triangularity \(\delta\) & 0.5 \\ Plasma current \(I_{p}\) (MA) & 1.25–1.5 \\ Non-inductive current, fraction & 1 \\ Magnetic field at the geometrical axis \(B_{t}\) (T) & 1.5 \\ Volume-averaged electron density \(<\)\(\epsilon_{DP}\) (10\({}^{20}\) m\({}^{-3}\)) & 0.7–1.0 \\ Total neutron yield \(S_{neut}\) (s\({}^{-1}\)) & 3–6 \(\times\) 10\({}^{17}\) \\ Neutron load onto the first wall (FW) (MW\(\cdot\)m\({}^{-2}\)) & 0.2 \\ Beam energy \(E_{b}\) (keV) & 130–140 \\ Beam heating power \(P_{NB}\) (MW) & 6–10 \\ Electron cyclotron heating power \(P_{EC}\) (MW) & 1–5 \\ \(H=\tau_{E}/\tau_{TB989}\) (\(y\), \(2\)) factor & 1.4–1.6 \\ Normalized \(\beta_{N}\) & 4–5 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: The FNS-ST parameters used in the FC simulations. Figure 2: \(D/\chi_{c}=0.4\) and \(n_{e}=8.5\times 10^{20}\) m\({}^{-3}\). The neutron intensity \(S_{neut}\) is a function of the fraction of tritium \(f_{core}T\) in the plasma for the D + T (**a**) and D (**b**) beams. Different colors correspond to the neutron intensity components contributing to the total neutron intensity \(S_{sum}\) (—). \(S_{bp}\) (—) is the intensity due to fast ion interaction with plasma, \(S_{pp}\) (—) is the intensity due to the plasma–plasma fusion mechanism, and \(S_{bb}\) (—) is the intensity due to interaction between the fast ions. DT reaction occurs as a result of two processes: the interaction of the fast deuterium ions with the thermal tritium (process 1) and the interaction of the fast tritium ions with the thermal deuterium (process 2). In this case, an increase in the neutron yield of the reaction of the beam-plasma interaction (Figure 2a, \(N_{bp}\)) with an increasing fraction of tritium implies that the contribution of process 1 to the DT reaction considerably exceeds that of process 2. Note that when the fraction of tritium in the plasma is \(f_{core}{}^{T}\) > 0.5 and the D beam is used, the neutron yield turns out to be higher (Figure 2b). For both types of the beam, the fraction of tritium in the plasma \(f_{core}{}^{T}\) can be different in different operating regimes (within the operating window of the \(n_{e}\) and \(D/\chi_{e}\) parameters) due to the considerable effect of the deuterium particle influx from the heating injectors on the isotope composition of the bulk plasma. For both types of the beam, the maximum possible neutron yield is reached at the maximum possible fraction of tritium in the plasma \(f_{core}{}^{T}(max)\) (see Figure 2). In this case, the pellets injected into the plasma consist of pure tritium (\(S_{pel}{}^{D}\) = 0). The parameter \(f_{core}{}^{T}(max)\) as a function of the \(n_{e}\) and \(D/\chi_{e}\) parameters is shown in Figure 3. For the D beam, in the ranges of low densities \(n_{e}\) = 7.0\(-\)9.0 \(\times\) 10\({}^{19}\) m\({}^{-3}\) and \(D/\chi_{e}\) = 0.2\(-\)0.3, the small values of \(f_{core}{}^{T}(max)\) can be explained by the low flux \(S_{pel}\) and, therefore, by the considerable effect of the \(S_{NB}{}^{D}\) flux along with the \(S_{pel}{}^{T}\) flux. Within the operating windows of the \(n_{e}\) and \(D/\chi_{e}\) parameters, the maximum possible fractions of tritium are 0.85 and 0.7 for the D + T (\(f_{NB}{}^{T}\) = 0.5) and D beams, respectively. For the scenarios with the D + T and D beams with identical plasma parameters (\(n_{e}\) = 8.0 \(\times\) 10\({}^{19}\) m\({}^{-3}\) and \(D/\chi_{e}\) = 0.4) but different fractions of tritium \(f_{core}{}^{T}\) (0.75 and 0.5, respectively), the absolute values of the \(S_{NB}\), \(S_{pel}\), and \(S_{sep}\) fluxes are shown in Figure 4a.