Measurement of He₂* density with an auxiliary measuring electrode in atmospheric pressure plasma jet

In this study, the density of metastable He₂* in an atmospheric-pressure plasma jet operating in helium with 0.001% nitrogen has been measured using an auxiliary measuring electrode technique. In the glow discharge mode, waveforms from two grounding electrodes, including one main discharge electrode and one auxiliary electrode, are captured. The isolated current peak formed by Penning ionization in waveforms from the auxiliary measuring electrode is identified to calculate the density of metastable He₂*. In our discharge environment, the helium metastable densities along the jet axis direction are between 2.26 × 10¹³ and 1.74 × 10¹³ cm^-3, which is in good agreement with the results measured by other techniques. This measurement technique can be conveniently applied to the diagnosis of metastable He₂* in an atmospheric-pressure plasma jet array.