Abstract
Spatially resolved optical diagnostics are applied to a free-burning DC arc in argon at atmospheric pressure. Densities of metastable and resonance -atoms are measured by laser atomic absorption spectroscopy (LAAS). The novel LAAS design allowed for an extended range of wavelength scan covering the complete Stark broadened line profile (∼ nm). High spatial resolution of 0.2 mm allowed measurements of atom densities and line profiles in the regions of high-temperature gradients. Besides absorbing -states, the radiating -states were measured using optical emission spectroscopy (OES). Results of the LAAS and OES measurements are compared with the nonequilibrium collisional-radiative model. Measurement of metastable states in the non-radiating regions near the cathode reveals the existence of a ‘collar’ effect. The interpretation of the effect with a focus on transport of resonance radiation is given, quantitative agreement between simulations and experiment is reached.
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