Thomson scattering on atmospheric-pressure air streamer discharge and photo-detachment of electrons from negative ions

Thomson scattering was applied to measure the time evolution of the electron energy distribution function (EEDF) in a pulsed positive streamer discharge in atmospheric-pressure air. It was necessary to correct for changes in the rotational Raman scattering spectra caused by fast gas heating within the streamer channel. Photo-detachment of electrons from negative ions resulted in stronger intensity and slower decay of the Thomson scattering signal than those expected from the actual electron density. However, the rapid thermalization of the photo-detached electrons enabled EEDF measurements during periods of low actual electron density. In the early phase of the secondary streamer, the measured non-Maxwellian EEDF corresponded to a reduced electric field of E/N = 130 Td. This value subsequently decreased to E/N = 80–100 Td and remained at that level until the end of the discharge. The EEDF trends were consistent with other observations, including fast gas heating and discharge optical emission. This study offers insights into the plasma physics of air streamer discharges and provides important considerations for the application of Thomson scattering to atmospheric-pressure air plasmas.