Reactivities of the reactions important for controlled fusion targets

For simulations of controlled fusion problems, 4 major reactions are conventionally ac-counted for. In the present work, we compare cross sections of many thermonuclear reac-tions between lightest elements. We show that along with the traditional reactions, con-siderable contribution can be given by the reaction $\mathrm{T+T}\to2n+{}^4\mathrm{He}$. At low temperatures, two reactions $\mathrm{D}+p\to \gamma+{}^3\mathrm{He}$ and $\mathrm{T}+p\to \gamma+{}^4\mathrm{He}$ also have considerable contribution, the rest reactions are likely to be neglected. For the outlined reactions, we perform a more thorough processing of experimental data and construct high-precision approximations. For the new reactions, the accuracy of the $\mathrm{S}$-factor is $2$–$6\%$ and that of the reactivities is $3$–$4\%$.