VUV–VIS spectroscopic diagnostics of a pulsed high-pressure discharge in argon

Abstract

High-pressure argon plasma, excited by a high-current pulsed volume discharge, has been investigated. Spatial-time VUV–VIS emission kinetics were used for the plasma diagnostics. A homogeneous discharge was obtained at a pressure of up to 10 bar. It was revealed that the spectral shape of the UV–VIS photorecombination continuum is a sensitive diagnostic tool for the constriction of the discharge. This shape changes because of the difference of the positive charge carriers in the arc (atomic Ar+ ions) and homogeneous (molecular ions) phases of the discharge. The intensity of this continuum is proportional to the square of the electron density. The experimental data and modelling show that the heating of electrons after the main excitation pulse is a very undesirable process. It suppresses the recombination flow in plasma, thus the kinetics of all excited species are spread in time with a decrease in the excimers densities. The electron collision-induced mixing effectively converts the reservoir of long-lived triplet molecules to fast-emitted singlet excimers. This mechanism is dominant in the production of singlet excimers.A realistic threshold density for the lasing of excimers of about 5 × 1015 cm−3 was estimated (the gain coefficient is 0.05 cm−1). This criterion could be realized in 10 bar of Ar by a homogeneous single pulse discharge pumping with a peak electron density of 2.4 × 1016 cm−3.