Dependence of the half widths of plasma-broadened hydrogen lines on reduced mass, temperature, and density.

Abstract

Using a relaxation theory of ion broadening we have performed calculations for ${\mathrm{L}}_{\mathrm{\ensuremath{\alpha}}}$, ${\mathrm{H}}_{\mathrm{\ensuremath{\alpha}}}$, ${\mathrm{P}}_{\mathrm{\ensuremath{\alpha}}}$, and ${\mathrm{L}}_{\ensuremath{\gamma}}$ for neutral hydrogen radiators. Our calculations span a wide range of electron density, temperature, and \ensuremath{\mu}, the reduced mass of the radiator and ion perturber. We identify four regions of qualitatively different influence of ion motion on the half widths at half maximum of hydrogenic line profiles. At sufficiently small \ensuremath{\mu}, the ion dynamics are impact in nature, while at very large \ensuremath{\mu} they are quasistatic. The half width increases with \ensuremath{\mu} in the impact region, and decreases with \ensuremath{\mu} as the quasistatic region is approached. In between these latter two regions, the half width reaches a maximum. We observe a similar dependence of the reduced width as a function of the plasma density. The temperature dependence is discussed as well. The ion dynamic influence on the half width is determined by the ratio of the relevant collision duration to the collisional coherence time for the transition. We discuss validity criteria for the ion-impact and quasistatic limits.