Measurement of electron velocity distribution function in a pulsed positive streamer discharge in atmospheric-pressure air

Laser Thomson scattering (LTS) was used for the first time to measure the non-Maxwellian electron velocity distribution function (EVDF) in an atmospheric-pressure-air pulsed positive streamer discharge. The air streamer was generated with specially designed electrode configuration which provided good spatial reproducibility. The LTS was conducted at a secondary streamer phase with a repetition rate of 2 Hz. To reduce the measurement error caused by intense rotational Raman scattering from N₂ and O₂, 20 000 LTS signals were accumulated. The LTS spectrum, which was a 1D-projected EVDF in the streamer, has shown a non-Maxwellian EVDF predicted by solving the Boltzmann equation. The measured EVDF exhibited good agreement with an EVDF calculated with E/N = 150 Td. Electron density at the initial phase of the secondary streamer was obtained from the LTS spectrum as 2.7 × 10¹⁴ cm^-3.