[en] Particle fluxes into the plasma and their velocity distributions are derived from the intensities and profiles of hydrogen and intrinsic impurity lines. In order to obtain local electron densities and temperatures, He- or Li-atom beams are injected, the line intensities of which yield the desired data. If excitation rates by plasma electrons are too low, more specialized diagnostics are used: e.g. the measurement of highly stripped ion densities and velocity distributions can be performed with the aid of charge exchange excitation by fast atom beams or the measurement of neutral atom densities and their velocity distributions near the wall by laser-induced fluorescence. Principles and typical results are discussed with special emphasis on the atomic data required, these being mainly excitation and ionization rate coefficients as well as transition probabilities of the light elements. (orig.)