Electric field and temperature patterns in lower-pressure streamer discharges*

The electric field is a fundamental plasma physical parameter. Determination of the electric field of streamers can become quite challenging as their velocity can reach significant values (generally ~10⁶ m/s). To investigate these highly transient electric fields, we deploy the line ratio technique by measuring the ratio of luminous intensities emitted by N₂(C-B) and N₂⁺(B-X) bands with a resolution of several hundreds of picoseconds. In our case, we investigated low-pressure discharges in nitrogen-containing gas mixtures operated at repetition frequencies of hundreds of Hz in a point to plate arrangement. The radiative transitions N₂(C³∏_u,ν=2)→N₂(B³∏_g,ν=5) and N₂⁺(B²∑_g⁺,ν=0)→N₂⁺(X²∑_g⁺,ν=0) bands were measured by ICCD camera to obtain a reduced electric field. Simultaneously, the whole recorded optical emission spectra were fitted with massiveOES software to obtain 2D maps of rotational/vibrational temperatures, giving a more detailed insight into the kinetic processes in streamer discharges.