Results of a Doppler spectroscopy study of the hydrogen Balmer alpha line in an abnormal glow discharge operated in pure hydrogen are reported. Measurements of line shapes are performed side-on to the discharge axis in a low electric field region of negative glow. The excessive Balmer alpha broadening is detected and its presence and linewidth is related to the collisions of fast hydrogen atoms with molecular hydrogen. The collision model enabled also an estimation of effective cross section data from the Balmer alpha axial intensity decay curves. Large excessive Balmer alpha line broadening in pure hydrogen and its dependence upon the direction of observation with respect to the electric field is in contradiction to the resonance transfer model, proposed byMills et al. in several publications [see, e.g., IEEE Trans. Plasma Sci. 31, 338 (2003)].

A spectroscopic method for the measurement of macroscopic electric field strength in discharges, based on Stark shifts of several helium emission lines with their forbidden counterparts, is presented. The shifts of forbidden and allowed π components are calculated for eight line groups of helium. For practical use, polynomial functions are provided for the shifts of line groups applicable in the visible range. The method is an extension and improvement of a previously established method for two line groups. Line fitting procedures are presented that take into account components of a given helium line group, provide higher accuracy compared to simple evaluation, and enable measurements of lower field values. The method and fitting procedure were experimentally tested and verified by measuring the field distribution in the cathode fall of a low pressure glow discharge. Due to its ab initio basis the presented method can be used for measuring electric field distributions in various types of discharges, independently of other plasma parameters and fulfillment of special conditions.

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Time development of electric field strength during radio-frequency sheath formation was measured using Stark polarization spectroscopy in a helium γ-mode radio-frequency (RF, 13.56 MHz) atmospheric pressure glow discharge at high current density (3 A cm −2 ). A method of time-correlated single photon counting was applied to record the temporal development of spectral profile of He I 492.2 nm line with a sub-nanosecond temporal resolution. By fitting the measured profile of the line with a combination of pseudo-Voigt profiles for forbidden (2 1 P-4 1 F) and allowed (2 1 P-4 1 D) helium lines, instantaneous electric fields up to 32 kV cm −1 were measured in the RF sheath. The measured electric field is in agreement with the spatially averaged value of 40 kV cm −1 estimated from homogeneous charge density RF sheath model. The observed rectangular waveform of the electric field time development is attributed to increased sheath conductivity by the strong electron avalanches occurring in the γ-mode sheath at high current densities.

Influence of discharge conditions on fast hydrogen atoms in glow discharge is investigated using Balmer alpha emission spectroscopy. Investigation was performed in two orthogonal directions of observation in pure hydrogen. The shapes of the profiles are examined together with the space intensity distribution of the excessively broadened Balmer alpha line. It was found that line profile, space intensity distribution, and energy distribution of exited atoms strongly depend on voltage, pressure, and the reduced electric field. This confirms that fast H atoms are generated in charge exchange processes and neutralization of ions at cathode surface and not in a non-field process.