Emission of the third continuum of argon excited by a pulsed volume discharge

Abstract

This paper presents the results of the observation of the third continuum band at 190 nm in a pulsed volume discharge at an argon pressure of 0.17–2 bar. The spatial-time kinetics of ultraviolet-visible photorecombination continuum and the third continuum of argon were measured and analyzed for the high- and low-current excitation regimes. Time-resolved imaging experiments with an intensified charge coupled device camera have shown that the second continuum of argon at 127 nm, Ar∗ lines and photorecombination continuum had a uniform distribution across the positive column of the discharge. However, the third continuum and Ar+∗ lines were emitted exclusively from the negative glow zone. This indicates to the existence of runaway electrons, accelerated in the electric field of the cathode layer and retarded in the negative glow zone. These electrons can achieve the energy of the cathode fall potential (130–250 eV). The radiative decay of the Ar22+ ions, created from Ar2+ precursors, is modeled. A good agreement has been achieved between the calculated and measured kinetics of the third continuum at different pressures, which supports the assignment of this continuum to the emission of Ar22+ ions. In contrast to the third continuum, the origin of the afterglow emission bands at 190 and 260 nm are connected with carbon-containing contaminants, accumulated inside the discharge chamber. These bands were disappeared during the gas circulation through the getter purifier.