Measurements of Spatial profiles of electron density and EEDF in a positive air-streamer discharge using laser Thomson scattering

Streamer discharges in atmospheric pressure air are used in various applications as an efficient reaction field for active species. In this discharge, the electron energy distribution function (EEDF), which determines the efficiency of active species production, is expected to clearly deviate from the Maxwell distribution. One experimental fact has been reported to support this prediction, but no detailed report exists yet. In order to obtain electron properties of streamer, we have attempted to measure the spatial and temporal variation of the EEDF using laser Thomson scattering (LTS) measurements. We use an air streamer discharge device that produces streamers with high spatial and temporal reproducibility using a special needle-electrode configuration. DC and pulsed power supplies were used as power sources, and a pulse voltage of 30 kV was applied to a 13 mm gap. The pressure in the reactor was set at 760 Torr and a synthetic gas of N2:O2=79:21 was supplied at 1000 sccm. The repetition rate of the discharge was set to a slow rate of 2 Hz to avoid changing the composition of the ambient gas. 532 nm wavelength, 10 ns pulse width, <0.1 pm spectral width, and 18 mj/pulse of a second harmonic Nd:YAG laser were used as the light source for the LTS measurements. The laser beam was focused onto the streamer using cylindrical lenses with focal lengths of 400 mm and 300 mm. In this case, measurements were taken at 1.5 mm, 4.5 mm, and 9 mm from the anode electrode tip. The laser was integrated 2000 times at the 1.5 mm position, 2500 times at 4.5 mm, and 3000 times at 9 mm. EEDF was greater than 100 Td at 1.5 mm and 4.5 mm, but less than 100 Td at 9 mm. Electron density decreased as increasing the length from the tip of the anode.