Emission and absorption diagnostics of a diffuse dielectric barrier discharge with multiple current peaks in helium at atmospheric pressure

Dielectric barrier discharge (DBD) is a simple means to sustain low-temperature diffuse discharges at atmospheric pressure. As atmospheric pressure plasma processing requires DBDs to work under various operating conditions, even diffuse discharges are often observed to exhibit multiple current peaks. In this work, multiple current peaks helium DBD is obtained by adding small concentration of argon in a nominally pure helium discharge. As the concentration of argon increases, multiple current peaks emerge while the discharge remains diffuse. Absorption spectroscopy is used to record the evolution of the He(23S) metastable atom. In a nominally pure helium discharge He(23S) metastable atom can reach up to 6 × 1011 cm−3. Even if quenching of the He(23S) metastable atom by argon is very effective, He(23S) density is found to still rise above 1010 cm−3 in a multiple current peaks discharge with 1100 ppm of argon. Optical emission spectroscopy of He n = 3 levels is also used to gain insights about the electron temperature (Te) through the means of a collisional-radiative model. For the multiple current peaks discharge with 1100 ppm of argon concentration, Te reaches about 1.0 eV during the primary peak but only about 0.3 eV during the secondary peaks.