Radiometric characterization of xenon positive column discharges

We use both experimental diagnostics and computational modelling to characterize the electrical properties and vacuum ultraviolet emission of positive column discharges in both pure xenon and mixtures of xenon with other rare gases. Discharge conditions include xenon pressures of 10-100 mTorr at room temperature, discharge currents of 100-500 mA and positive column diameters of 1.1-5 cm. Our primary interest is the efficient generation of large quantities of ultraviolet radiation for use in fluorescent light sources. We therefore focus on the total output of atomic xenon resonance radiation at 147 nm, reported in units of watts of 147 nm radiation per unit length of positive column, and also the efficiency by which electrical input power is converted into 147 nm radiation. Over the range of discharge conditions considered, we observe outputs in excess of of discharge length and efficiencies in excess of 80%, but we also find that there is a strong tradeoff between efficiency and output, and that these two figures of merit cannot be simultaneously maximized. A change in the behaviour of the discharge is observed to occur near 25 mTorr in 2.2 cm diameter tubes and is attributed to the transition from a discharge sustained by multistep electron-impact ionization to one sustained by single-step electron-impact ionization.