Influence of ultraviolet illumination on microdischarge behavior in dry and humid N-2, O-2, air, and Ar/O-2: The Joshi effect

The influence of UV illumination on the behavior of silent electrical discharge streamers (microdischarges) in dry and humid gases (nitrogen, oxygen, air, and Ar/O-2 mixtures) is presented. A commercial low-pressure mercury lamp, which was spectrally calibrated, provides UV light. The UV irradiance power coupled into the discharge cell is also calculated. The transferred charge per mean microdischarge (in a voltage half-cycle) was measured for a pin electrode assembly, configured to deliver either M-G+ transitions (electrons going from metal towards dielectric) or M+G- transitions (electrons going from dielectric to metal). The total transferred charge is recorded by monitoring a charge versus voltage plot (Lissajous figure). When illumination is restricted to the gas alone, both the total transferred charge and the individual-microdischarge transferred charge remain constant for either transition (M-G+ or M+G-). However, when the dielectric is illuminated, a marked decrease in the individual-microdischarge transferred charge is observed for M+G- transitions in some gases. For this case, a greater number of microdischarges must occur in a half-cycle to keep the total transferred charge constant, thereby creating more homogeneous discharge conditions. (C) 1997 American Institute of Physics.