[en] In the case of neutral injection into a hot-electron target plasma, the use of the existing Fokker-Planck codes is greatly complicated by the fact that the scale of the energies and times of the confined ions and electrons is very large. To avoid this difficulty, a simplified multi-species model is set up, in which each species is described by time-dependent density and energy equations with analytical approximations for the interactions between the species. During the neutral injection, instantaneous high values of the ambipolar potential (higher than the half value of hot-ion energy) may appear, but do not prevent hot-ion density build-up. However, the hot-electron target plasma must not be maintained for a too long time. Numerical runs are performed with typical target parameters: density 2x10¹³cm^-3, electron energy 30 keV, ion energy 400 eV, time duration during which the target density is maintained 1 ms. Hot-ion density, a few 10¹⁴ cm^-3, can be achieved with a neutral beam of 100 A, 20 keV. (author)