Characteristic Study Of Stable Gas-liquid Discharge Plasma In Oxygen At Atmospheric Pressure

In this paper,a suitable capacitor was employed to quantify the charge number（prevent the increase of discharge current density）and generate a stable diffusion oxygen plasma.There were four capacitors connected in the discharge circuit in turn with capacitance of 50 p F,75 p F,150 p F and 300 p F respectively.The discharge power and waveform of voltage and current were analyzed to confirm the best coupling capacitor.Dynamic evolution of electrical characteristics and discharge images were measured to investigate the discharge modes and their transitions when the discharge parameter of applied voltage was changed.The emission spectral intensities of active species were calculated by measuring plasma emission spectra.The emission spectral band of the nitrogen second positive band N₂（C₃Πu→B₃Π_g,Δv=2）was simulated to analyze the changing process of plasma gas temperature and vibrational temperature by adding 10 % nitrogen to work gas.Finally,the Stark broadening of hydrogen atom Balmer spectral lines of H_β was calculated and simulated,then electron density was calculated as a function of applied voltage.Main achievements:1.Plasma voltage and current waveform generated by the discharge circuit with different capacitors was measured to analyze the liming effect of capacitance value.Results indicated that the larger the capacitance value,the smaller the voltage required to form a stable discharge;the smaller the capacitance value,the higher voltage of discharge breakdown.Discharge power in a single cycle was also calculated,which found the larger the capacitance value the more obvious phenomenon of limiting voltage increasing at both ends of plasma.The capacitor with a capacitance of 75 p F was selected as the best suitable coupling capacitor.2.As the asymmetry of electrode structure,the plasma discharge modes and transition process were also asymmetry in positive and negative half cycle.With the increase of applied voltage,plasma discharge mode transformed from streamer discharge to glow discharge and then to arc discharge in positive half cycle,from corona discharge to arc discharge in negative half cycle.With the plasma discharge mode transition,discharge local heating in the channel transformed to integral heating,the plasma discharge area increased,and the stability also increase.3.Plasma emission spectra indicated that there were plenty of active species generated include hydroxyl radical OH（A-X）,oxygen atom O and amount of hydrogen atom H,then their emission spectral intensities were calculated.Plasma gas temperature was simulated by Specair.With applied voltage increasing,plasma gas temperature also increased in a same discharge mode,the increase of plasma gas temperature is also increased within mode transition.According to the gas temperature,the broadening of HWHM（full-wide at half-maximum）of hydrogen atom emission spectra was calculated and simulated to calculated plasma electron density.The mode transition caused by the increase of applied voltage made electron density decrease.4.In plasma treated water,there were trace amounts of hydrogen peroxide,nitrate and nitrite,and a small decline of PH.The formation of hydrogen peroxide was generated by the reaction of hydroxyl and oxygen atom with water molecules.Because oxygen impurity gas and water contained and dissolved a small amount of nitrogen,discharge plasma reaction generated nitrate and nitrite dissolving in water liquid.The formation of these reactive species resulted in a decrease in PH value of the solution.