Divergence of the Stark collision operator at large impact parameters in plasma spectroscopy models.

The divergence that occurs at large impact parameters in Stark collision operators is examined for low-density hydrogen plasmas. In a previous work [J. Rosato, H. Capes, and R. Stamm, Phys. Rev. E 86, 046407 (2012)], we showed that the correlations between a radiating atom and the charged particles surrounding it affect the mean evolution of the atom, resulting in a mitigation of the Stark broadening near the line center. In this work, we examine the physical mechanism underlying this mitigation with an approach inspired from the standard semiclassical impact model. Our approach accounts for the atom-perturber correlations in a simple fashion, through a cutoff at large impact parameters, and embraces the impact model in the weakly coupled plasma limit. Comparisons with numerical simulations are performed and indicate a good agreement.