Spatially resolved absolute intensities of the atomic lines Hα, Hβ, Hγ, and Hδ have been measured and analyzed in pure hydrogen plasma in the linear plasma device PSI-2. Two regimes have been investigated, with nominal (0.04 Pa) and elevated (0.5 Pa) gas pressure in the sample chamber. The measurements have been compared with local 0D calculations taking into account radiation from H(n=1), H2, and H2+ channels. A baseline plasma chemical mechanism developed in magnetic fusion research was applied to calculate the H2+ density. Both the plasma chemical mechanism and the population factors applied are based on Sawada–Fujimoto collision-radiative model of atomic and molecular hydrogen. The calculations were found to reproduce both the absolute radiation and the line radiation intensity ratios measured in the 0.04 Pa experiment with electron temperature Te = 2–10 eV and electron density ∼5 × 1017 m−3. An exception is the Hα/Hγ intensity ratio, which tends to be overestimated by the model. The calculations suggest that the majority of the observed Balmer radiation in this regime is due to the H2+ channel. At the same time, both the applied simplified approach without detailed transport modeling and the baseline mechanism were found to be inappropriate for the 0.5 Pa experiment with reduced Te = 1–5 eV. This experimental regime can serve as a benchmark of more sophisticated hydrogen plasma models.
Kotov et al. (2026) studied this question.