Radiation spectroscopy of non-stationary plasma at high densities of excited noble-gas atoms

Abstract

Theoretical and experimental study of the ionization-recombination relaxation in the pulsed discharge plasma has been carried out at high density of the excited noble-gas atoms. The background electron density Neb was between 109 and 1010 cm-3, the density of the neutral atoms Na was within the limits 1017-1018 cm-3, and the reduced electric field E/Na varied between 5 and 25 Td. The excited atom and electron density growth induced by the stepwise electric field variations was found to be of an explosive character due to the accumulation of atoms in the lowest electronically excited states. When the excited atom density exceeds the electron concentration essentially, the binary chemi-ionization reactions of the excited atoms were shown to play a principal role in the kinetics of the excited atoms and electrons. The theoretical description was performed in comparison with the experimental study of the kinetics of the excited atoms and electrons. Approximate analytical expressions have been obtained for the de-excitation development. The theoretical model allows calculation of the temporal dependence of the emission spectra and the determination of the effective rate coefficients of the direct excitation by electron impact from the ground state to the np5(n+1)s levels. The effective rate coefficients of the chemi-ionization processes for binary collisions between excited noble gas atoms have also been obtained. Calculation and experiment are in good agreement.