Electrical and optical emission measurements of a capillary dielectric barrier discharge

We report a capillary dielectric barrier discharge (Cap-DBD) plasma operated in atmospheric pressure air. The plasma reactor consists of metal wire electrodes inside quartz capillary tubes powered with a low kilohertz frequency AC high voltage power supply. Various reactor geometries (planar, 3-D multilayer, and circular) with wall-to-wall separation ranging from zero up to 500 micron were investigated. For the electrical and spectral measurements, three reactors, each with six tubes, six inches in length, were assembled with gap widths of 500 micron, 225 micron, and 0 micron (i.e. tubes touching). The discharges appear homogenous across the whole device at separations below 225 micron and turned into filamentary discharges at larger gap spaces. The operating voltage was generally around 3-4 kV (rms). The power consumption by the Cap-DBD was calculated using voltage/charge Lissajous figures with observed powers of a few watts to a maximum of about 14 W for the reactor with no gap spacing. Further studies of optical emission spectroscopy (OES) were employed to evaluate the reactive species generated in the microplasma source. The observed emission spectrum was predominantly within the second positive system of N ₂(C₃π_u - B³ π_g) and the first negative system of N⁺₂ (B²σ ⁺_u-X² Σ⁺_g).