A study of physical processes in microplasma capillary discharges

Abstract

We continue the research of low-pressure capillary discharge lamps of 500 μ m in radius in Ar/Hg, Kr/Hg and Xe/Hg mixtures. In the previous paper, an experimental approach which combines the optical emission spectroscopy (OES) and tomographic methods was developed to study the capillary discharge. The present work is focused on interpretation of the tomographic reconstruction results for understanding the physical processes occurring in a capillary plasma. Analyzing the results of reconstruction, it was concluded that the radial profiles of Ar, Kr and Xe emission coefficients are in a good agreement with the Schottky theory. According to the Schottky model, ionization processes in plasma are balanced by electrons and ions transfer to the wall due to ambipolar diffusion. Using the Schottky model, the electron temperature in an Ar/Hg capillary lamp was estimated. The value of the temperature was higher in comparison with that in a large-scale Ar/Hg discharge. A simplified model describing the excited atomic states kinetics is analyzed. This model agrees with all radial profiles of emission coefficients, obtained by using a tomography approach, except one for mercury line of 546.07 nm in the Ar/Hg capillary lamp. We suppose that the simplified model did not include the processes which were important for the mercury population balance in Ar/Hg mixture. It was proposed that the transfer of high-excited mercury atoms may play an appreciable role in the Ar/Hg capillary discharge.