Influence of High Voltage Microsecond Pulse Polarities on a Helium Atmospheric Pressure Plasma Jet

Atmospheric pressure plasma jets (APPJs) are plasma sources having plenty of applications in surface modification, environment protection, biological and medical applications. In this experiment, APPJ was simply consist of a quartz tube, a powered electrode, and an electrically grounded electrode. A 5~10 kV of high voltage (HV) pulsed DC was applied to the APPJ to produce helium gas discharge. Positive and negative polarities of the HV pulses were separately supplied to the APPJ. To characterize the APPJ, line intensities of He and other species such as O, N₂, N₂⁺ and OH of plasma spectra measured by optical emission spectroscopy. He 2³S metastable atom density was measured by laser absorption spectroscopy. Plasma properties such as electron density and electron temperature were deduced from the optical experiment. Speed of gas discharges propagating in the way of gas flow was dramatically changed depend on the polarities of HV. Finally, the different physics of plasma discharges in the APPJ depended on the polarities of the applied HV pulsed DC was discussed.