Numerical predictions of the power balance in the positive column of a low-pressure Ba discharge

Summary form only given. Barium has been suggested as a low-pressure gas discharge system which may possess a very high luminous efficacy. This suggestion is based on the similarity of Ba´s electronic structure to that of sodium, which is the basis of the most efficacious light source available. However, the Ba resonance wavelength at 553 nm is closer to the peak of the eye sensitivity curve than the Na resonance doublet at 589 nm. This difference in wavelength gives Ba a 30% higher lumen output than Na for the same power emitted from the discharge on the resonance line. Ba ions have also been shown to contribute a significant fraction of the visible radiation under some operating conditions. We have constructed a relatively sophisticated fluid model of the low-pressure Ba discharge positive column that incorporates a large number of measured and calculated cross-sections for collisional processes involving Ba. The model includes eight excited states of neutral Ba as well as four excited states of the Ba ion. We will discuss trends in the power balance as a function of the ´external´ parameters, as well as some of the important ´internal´ mechanisms including ionization out of low-lying metastable levels, buffer gas quenching of the resonance level, ambipolar cataphoresis, and radiation production by the ions.