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Investigation of the population density of excited atomic hydrogen in negative hydrogen ion sources based on a collisional-radiative model

Collisional-radiative (CR) models are useful to analyze the dynamic process of excited states and support the interpretation of excited population densities measured for example by optical emission spectroscopy (OES). A CR model of atomic hydrogen is described, in which the population densities of the excited states are coupled to the densities of ground state H, H2 and H2+. The three coupling channels, namely excitation of H, dissociative excitation of H2 and dissociative recombination of H2+, usually account for the main contributions to the excited hydrogen atoms in cesium free negative hydrogen ion sources. The population densities of excited hydrogen atom are presented for each channel. They have a similar dependence on electron density for the three channels. Furthermore, the influences of varying electron energy distribution function (EEDF) on the excited state density are discussed. Finally, the described CR model is applied to OES in an ICP hydrogen discharge and the estimated plasma parameters are given.