A radiometric and electrical characterization of low pressure dc positive column sulfur discharges

Abstract

The dc positive column sulfur (S) and S–Ar discharges have been studied over a wide range of operating conditions. Even though the equilibrium partial pressure of S2 is low in the 50 °C–200 °C temperature range investigated here, the primary radiating molecule in these discharges is S2. Electronic collisions dissociate S8 to produce the radiating S2 molecules at densities far in excess of the equilibrium density. The majority of the spectral emission occurs in the 2800–3500 Å range. The spectrum observed from these discharges corresponds nicely to that obtained from dc discharges at much higher temperatures. The radiation output has been studied as a function of input power, wall temperature, buffer gas pressure, discharge radius, and cold spot temperature. The absolute efficiency of the discharge in generating near-ultraviolet radiation has been measured and the results are presented for many areas of the multidimensional parameter space. The maximum efficiency of ultraviolet and visible emission obtained was approximately 17%.