The influences of shielding gas and quartz tube on discharge properties and reactive species productions of nanosecond pulsed gas-liquid discharge

In this paper, shielding gas (He) and shielding quartz tube (straight tube and conical tube) is added to nanosecond pulsed He gas-liquid discharge (G-LD) to limit the air diffusion into plasma, and for the purposes of enhancing the plasma volume and productions of cOH and H2O2. The plasma properties, including current-voltage waveforms, the temporal-resolved discharge images, optical emission spectra, gas temperature, electron density, and the cOH and H2O2 productions are analyzed and compared among different discharges generated under the cases of no shielding, shielding He gas, shielding straight tube, and shielding conical tube. The results show that adding extra shielding gas and tubes in the discharge reactor can decrease the gas temperature and electron density, but enhance the plasma volume and area of plasma-liquid interface in comparison with no shielding case. Besides, the addition of shielding gas has the most benefit for enhancing the productions of cOH and H2O2 produced by G-LD. Adding a shielding conical tube slows down the decrease extent of cOH and H2O2 productions caused by increasing discharge gap. When the discharge gap excesses 6 mm, adding a shielding conical quartz also has an obvious increase effect on the production of cOH and H2O2 in compared with no shielding case. While adding a shielding straight tube with small diameter has a little effect on H2O2 production, even a negative effect on cOH production.