Center-of-mass effects for hydrogen atoms in a nonuniform electric field: applications to magnetic fusion, radiofrequency discharges, and flare stars

Abstract

We study whether or not the Center-of-Mass (CM) motion and the relative motion can be separated for hydrogen atoms in a nonuniform electric field. First, we show that in the general problem of two charges in a nonuniform electric field, the CM and relative motions, rigorously speaking, cannot be separated. Second, we use an approximate analytical method of the separation of rapid and slow subsystems to achieve a pseudoseparation of the CM and relative motions for hydrogenic atoms/ions in an arbitrary nonuniform electric field. Third, we further develop these results for the case of a hydrogen atom in the nonuniform electric field, where the field is due to the nearest (to the hydrogen atom) ion in a plasma. Fourth, we apply the results to the ion dynamical Stark broadening of hydrogen lines in plasmas. Fifth, we present specific examples of laboratory plasmas (e.g., magnetic fusion plasmas or radiofrequency discharges) and astrophysical plasmas (e.g., in atmospheres of flare stars) where the allowance for these CM effects leads to a significant increase of the width of hydrogen spectral lines.