[en] Local atomic hydrogen densities inside plasmas of the Compact Helical System (CHS) were measured using later induced fluorescence tuned to H_α, and the results were compared with those calculated using a neutral particle simulation code, in order to determine the penetration energy of hydrogen atoms from the chamber wall into the plasma. The results of these and supplementary measurements of H_α emission intensities using CCD cameras and photomultipliers at various toroidal positions yielded local atomic hydrogen densities distributions throughout the whole plasma. The distribution of the particle source rate was evaluated from the atomic hydrogen distribution, and then the radial particle flux profile was obtained from a particle continuity equation. Estimated errors for the latter were ± 30% at an absolute level and several per cent in the profile shape. The radial particle flux thus obtained is valuable for evaluations of particle diffusion coefficient and convection velocity. (author). Letter-to-the-editor. 16 refs, 6 figs