Line profiles for hydrogen including the case of dense plasmas are investigated on the basis of a many-particle approach. Using a Green s-function technique, electron contributions to the shift and broadening from both separate-level and interferencelike terms are considered consistently. The theoretical approach to the line profile has been improved by including dynamic screening of collisions, contributions from hn =0 transitions, and cross-term contributions not only to the broadening but also to the shift of the line. As an example, the line profile of H has been considered. An analysis of details of the second-order approximation with respect to the atom-plasma interaction is given, avoiding the noquenching and dipole approximations. The effect of dynamic screening for high electron densities is investigated. Deviations from the linear dependence between the electron-shift contribution and the density are expected for H for n, &2X10" cm at temperatures of about 10000 K. PACS number(s): 52.25.Rv, 32.70.Jz I. INTRODUCTIGN

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An alternating current (ac) high-pressure mercury arc has been experimentally investigated, and the results have been compared with model calculations. In the model, only radial dependencies are considered, and a careful treatment of the radiation transport is included. The absolutely measured side-on radiance in the visible and near ultraviolet spectral range can now be quantitatively reproduced by this model starting from the measured arc current. Agreement between the measured and calculated radial temperature profile can be obtained only by taking into account the time-dependent behavior of the investigated ac arc. The calculated field strengths agree with the measured ones only if more recent values of momentum transfer cross sections for the calculation of the electrical conductivity of mercury have been used. The time-dependent pressure in the discharge is determined via the electrical conductivity using Ohm’s law, the radial temperature distribution, and the electrical field strength.

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