Simulation And Experimental Research On Atmospheric Pressure Nanosecond Pulsed Discharge Plasma

As an effective method to generate atmospheric-pressure non-equilibrium plasma, atmospheric-pressure nanosecond-pulsed discharge has promising applications in pumping pulsed CO2laser and excimer laser, plasma display panel, plasma medicine, pollution control, nanofrabrication, flow control, plasma stealth, etc. Compared with other generation methods, it has higher yields of UV radiation, oxygen atom and ozone, higher plasma density and peak current, and lower energy comsuption. In this thesis, atmospheric pressure nanosecond pulsed discharge is investigated experimentally and simulatively.In simulation study, a PIC-MCC modeling, which is suitable for atmospheric-pressure nanosecond-pulsed discharge, is set up. In order to adapt the characteristics of atmospheric-pressure nanosecond-pulsed discharge, the special methods, implicit PIC algorithm and renormalization algorithm based on energy, have been utilized in the modeling. In addition, multiple MCC processes method is put forward to deal with the extremely high collision frequency of the electron in atmospheric pressure.Firstly, using the PIC-MCC modeling, the process of atmospheric-pressure argon nanosecond-pulsed discharge with typical parameters is studies in detail. The evolutions and distrubutions of plasma characteristics are reported. These results confirm the accuracy of the PIC modeling. Based on the evolution of effective temperature, the discharge process can be divided into seven phases, and the evolution and mechanism of the plamsa in seven phases are analysed.On the basis of discharge process analysis, the impact of discharge parameters, such as second electron emission ratio, plateau voltage, pulse rise time, initial charged particle density, and neutral gas temperature are studied simulatively. It is found that the impact of second electron emission ratio can be ignored in several nanoseconds pulse, and the plateau voltage in the pulse waveform is a major factor controlling the final charged particle density in the plasma bulk. The growth of electron density and effective electron temperature is slowing with longer pulse rise time, and the initial charged particle density can only affect the built-up time of cathode sheath. What is more, the neutral gas temperature influences the growth speed of electron density, maximum effective electron temperature, and the built-up time of cathode sheath. Finally, the similarities and differences of the nanosecond-pulsed discharges in three different noble gases (helium, neon and argon) are compared and analysed. The differences of specific charge and cross section lead to the quasi-Maxwell energy distribution of electron before the cathode sheath formation, and the electron peak near the cathode sheath in helium and neon. However, the evolution processes and the electron energy distributions after the cathode sheath formation are similar in these three gases.The experimental study contains the measurements of neutral gas temperature and energy injection ratio between cathode sheath and plasma bulk in atmospheric-pressure nanosecond-pulse discharge.In order to measure gas temperature during the discharge, the method of fitting plasma emission molecular spectra is adopted. Firstly, the nitrogen second positive spectra system is analyzed. On this basis, the time-resolved emission spectra are measured with low and high resolution grates. Compareing the spectra radiation intensity with the discharge voltage waveform, it can be found that high intensity radiation has appeared before discharge breakdown. The rotational temperatures of four vibration bands (0-0,0-1,0-2and0-3) in two different times can be fitted by the high resolution spectra, which coincide with each other.In order to study the injection energy ratio of cathode sheath, a new method, which using cathode shock wave velocity, is put forward to measure the cathode sheath temperature and the energy injection ratio between cathode sheath and plasma bulk. Firstly, the time sequence flow field interferograms after discharge are acquisited by the ICCD camera. After that, the cathode shock wave velocities in different discharge conditions are extracted from these interferograms to calculate the cathode sheath temperature and the energy injection ratio. It is found that the cathode sheath temperature and the energy injection ratio are determined by the specific energy deposition and the breakdown delay time respectively.These experiment studies reflect the process and law of the nanosecond-puled discharge, and offer the methods for systematic experimental study of atmospheric-pressure nanosecond-pulsed discharge with less special and temporal scale.