Spectroscopic Study of Low-Frequency Helium DBD Plasma Jet

Atmospheric-pressure helium plasma jet has been studied by optical emission spectroscopy and electrical measurements. Streamer/bullet properties of the plasma jet are observed in the positive voltage half cycle, whereas in the negative jet, they operate more as a glowlike atmospheric-pressure discharge. This is revealed by spatially resolved measurements of intensity distribution of typical excited species and by electric field measurements based on Stark polarization spectroscopy. Obtained radial distribution of the axial electric field of the bullet shows that the ring-shaped structure of the light emission is a consequence of such electric field distribution. Gas temperature distribution over the jet is obtained by Boltzmann plot of rotational lines of N₂⁺ and OH bands. Gas temperature is found to be about 310 K, favorable for the biomedical applications.