Numerical Study On Atmospheric Radio-frequency Glow Discharges Assisted By High-voltage Pulses

Recently,atmospheric pressure radio frequency glow discharge is one of the most effective methods used to generate plasmas.Comparing with the low pressure glow discharge,it has many advantages on cost(not requiring expensive vacuum equipment),efficiency and exhibiting highly homogeneous characteristics.It shows potential applications,such as surface modifications,material synthesis,and biological sterilization.However,due to the instability of radio-frequency glow discharge,the application scope is limited.Compared with the radio-frequency glow discharge,pulsed atmospheric glow discharge has higher electron generation efficiency,higher mean electron energy and more effective in the surface treatment of materials.By combining their advantages,we introduce a high-voltage pulse to assist radio-frequency glow discharge in order to obtain high intensity and stable discharges.Many experiments have been carried out and proven the advantages of pulse-modulated discharge.However,there are still many issuses that is not well understood such as the mechanism of high-voltage pulse assisted discharge and the influence of pulse parameters.Here we present numerical simulation study on atmospheric radio-frequency glow discharges assisted by high-voltage pulses with the background gas of Helium.Firstly,we investigate the discharge characteristics and mechanism of atmospheric radiofrequency glow discharges(with and without dielectric barriers)assisted by highvoltage pulses by using one-dimensional self-consistent fluid model.It is found that high-voltage pulse generating strong electric field near the electrodes and the discharge current peak occurs.After the pulse stops,the current density reduced quickly while the plasma density drops off slowly.It shows that the high-voltage pulse can enhance the plasma density of RF discharge.The waveforms of discharge current density show that one discharge event occurs during the high-voltage pulse with bare electrodes and two distinct discharge events occur at the rising and falling phases of high-voltage pulse with dielectric barrier electrodes,respectively.The spatial profiles of electron density shows that the electrons are trapped in the plasma bulk in both discharges.Since the strong electric field in the sheath region to accelerate electrons and ions,the electron energy increases.The maximum electron energy appears near the electrodes,which is much higher than that in the plasma bulk.Furthermore,the influence of different pulse parameters(amplitude,duration,rising and falling time and the time interval between high-voltage pulse and rf discharge)on the discharges(with and without barriers).The study of different voltage amplitude reveals that the discharge current peak and electron density will raise with the rising amplitude.We found that the pulse duration controls the time instant of discharge,but have little influence on the current and electron density.With the shorter the rising and falling time,the higher discharge current,gas voltage,electron density and mean electron energy can be achieved.The influence of time interval is similar to that of the pulse duration,which only controls the time instant of discharge.