Modeling of low-pressure barium-rare-gas discharges

Abstract

The fundamental principles of low-pressure discharges containing a minority of barium (5-20 mtorr) in a rare gas at pressure 1-20 torr have been investigated, using a numerical model of the positive column, with a view to assessing the potential of these discharges as a light source. The principle resonance line of neutral barium is from the 6p(1)P1 state and has a wavelength of 553 nm, which is close to the center of the photopic eye response curve. This green line can be augmented by radiation from barium ions to produce a "white" light. Published cross-section measurements suggest that the 6p(1)P1 state is heavily quenched by collisions with rare-gas atoms, reducing the radiation efficiency. The measured quenching cross section is much smaller for neon than other rare gases. Spectral line broadening by these same collisions, on the other hand, enhances the escape of radiation from the discharge through the line wings. The present paper reports the results of detailed calculations of the influence of rare-gas quenching and line broadening on discharge parameters (power balance, electric field, electron temperature, and density) as a function of discharge current, rare-gas, and barium vapor pressure.