Application of the line shape measurements in the linear plasma device PSI-2 as a benchmark of hydrogen plasma chemistry

High resolution spectra of the lines H α , H β , H γ emitted from the pure hydrogen plasma of the linear device PSI-2 have been measured and analysed. The plasma parameters are: electron temperature 2–10 eV, electron density ∼ 5 ⋅ 10 17 m −3 , gas pressure 0.04 Pa. The spectral lines can be decomposed into two Doppler broadened components, one of which is rotating with plasma. A plasma chemical model based on the rate coefficients from the data sets AMJUEL and HYDHEL, as well as Sawada–Fujimoto population factors have been applied to analyse the measurements. Partially predictive model calculations reproduce the experimental fraction of the rotating ionic component in the middle of the plasma column, but discrepancy was found at the plasma edges. The results confirm quantitatively the hypothesis that the ionic component is formed by dissociative recombination of molecular ion H 2 + . The comparison between the measured ionic fraction of the spectra with the calculations provides a good validation test of the applied plasma chemical model. The local disagreement indicates the limitations of the model especially at lower electron temperatures. The decomposition of Balmer lines into unshifted and rotating component has found to be a useful tool for plasma chemistry validation.