Characteristics of a Nanosecond Pulsed Bubble Discharge in N2/O2 Atmospheres

Nanosecond pulse power is employed to excite a N-2/O-2 bubble discharge using hollow needle electrode underwater at atmospheric pressure. The discharge images, waveforms of applied voltage and discharge current, and optical emission spectra are recorded to investigate plasma characteristics and diagnose the active species in the discharge region with varying O-2/N-2 proportion, and the spectrophotometry is applied to measure the H2O2 concentration in the liquid phase. A glow-like discharge is obtained with bubbling N-2, whereas the discharge transfers to a filament mode when mixing O-2, and obvious filament regime is built when the volume proportion of O-2 is above 80%. With the increase of O-2 proportion, the emission intensity of O increases rapidly but that of OH decreases sharply. The effects of pulse voltage and pulse repetition on emission intensity are studied to optimize discharge parameters. The liquid pH values have an uptrend within plasma treatment for 30 s and then decrease with increasing treatment time.