Stark broadening of Hα and Hβ in ionized gases with space-charge field

In ionized gases created by prebreakdown discharges, the heat transfer from electrons to heavy particles is weak since it is often governed by electron-neutral collisions. Thermal ionization does not take place and the conductivity can be small enough to allow space-charge fields to appear. Under these conditions, the low frequency component of the field, which acts on the radiating hydrogen atom, is due to the vector sum of the ionic microfield and the space-charge field. Thus, a spatial anisotropy of the low frequency distribution of the field appears, which is derived in this paper and introduced in the general expressions of hydrogen-line broadening. It is shown that the emitted profile varies spatially and that the value of the space-charge field can be deduced from the difference of broadening between the light emitted perpendicular and parallel to this field. Calculations for H_α and H_β are given within the range of validity of the expressions used.