Optical diagnostics of a surface-wave-sustained neon plasma by collisional-radiative modelling and a self-absorption method

A surface-wave-sustained microwave discharge in a coaxial tube configuration in neon at low pressure (300-700 Pa) was studied by optical emission spectroscopy. Spectra of the discharge were analysed by a self-absorption method and a collisional-radiative model. The self-absorption method was used to determine the densities of neon metastable states. The collisional-radiative model, using these densities, was applied to determine the axially resolved electron temperature and the reduced electric field strength in the discharge from the optical spectra. Two types of electron distribution functions were used in the calculations-a Maxwellian distribution function and a solution of electron Boltzmann kinetic equation. The spatially averaged neon metastable densities were in the range (0.12-0.53) x 10(16) m(-3) and (3.4-4.1) x 10(16) m(-3) for 1s(3) and 1s(5) states, respectively. The axial profile of the electron temperature was found to be approximately constant around 1.3-1.6 eV depending on the pressure. The reduced electric field strength decreased along the plasma column in the range 16.5-6.0 Td depending on the pressure. A large influence of gas cooling along the plasma column on the determined reduced electric field strengths was observed.