Characteristics Diagnosis And Electric Field Simulation Of Atmospheric Pressure Diffuse Discharge Plasma Under Oxygen-Enriched Environment

Atmospheric pressure diffuse discharge plasma is uniform discharge across the entire electrode gap,which has the advantages of high energy density,large discharge area,and gas temperature close to room temperature.It is the main form of discharge in applications such as material preparation and modification.However,under atmospheric pressure conditions,the discharge is easily transformed into unstable discharge forms such as the filament,spark discharge,or arc discharge,which are prone to cause damage to the sample.In view of this background,in this thesis,a specially designed plasma generator with a floating electrode structure was used to obtain a stable large-area diffuse discharge plasma in an open oxygen-rich environment.The emission spectra diagnosis and electric field simulation studies were conducted to facilitate the application of dispersive discharge plasma in the fields of material preparation and modification.The main research contents of this thesis are described as follows:（1）The generation and electric field simulation of atmospheric pressure diffuse discharge plasma with floating electrode.The breakdown voltage and discharge mode transition voltage of two plasma generating devices with and without floating electrode structure as well as the electric field and potential distribution of the above two plasma generating devices were measured and calculated.The generation mechanism of the diffuse discharge plasma was analyzed in combination with the discharge image and the discharge light intensity distribution in the plasma generator with floating electrodes;The results show that the floating electrode structure can effectively broaden the applied voltage range of the stable discharge（corona discharge and diffuse discharge）and is conducive to maintaining the stable diffuse discharge;The electric field and potential simulation of the two plasma generating devices show that a uniform electric field is formed at the surface of the floating electrode,which makes the floating electrode conducive to maintaining the uniformity and stability of the discharge;In the plasma generating reactor with the floating electrode structure,the gas flow rate has no significant effect on the discharge morphology of the diffuse discharge plasma;The discharge morphology and the discharge light intensity distribution show that the plasma generator with floating electrode structure produces a more uniform electric field and no obvious discharge channel contraction during the discharge process.（2）Emission spectra analysis of atmospheric pressure diffuse discharge plasma.A emission spectra diagnosis study of diffuse discharge plasma was carried out using a plasma generating device with a floating electrode structure.The main active particle species in the atmospheric pressure floating electrode diffuse discharge and the related physicochemical processes of their generation and quenching were revealed.In addition,the effects of applied voltage and gas flow rate on the emission spectra of diffuse discharges from atmospheric pressure floating electrodes were investigated.The results show that the diffuse discharge plasma mainly contains N₂（C³Π_u）,N₂（B³Π_g）,N₂（A³Σ_u⁺）,N₂⁺（B²Σ_u⁺）,and O（3p⁵P）active particles,among which N₂⁺（B²Σ_u⁺）mainly originates from direct electron collision excitation and O（3p⁵P）mainly has two production pathways.The higher the applied voltage,the stronger the electric field intensity,which can generate more high-energy electrons to collide with neutral particles.This leads to a significant increase in the emission intensity of N₂（C³Π_u）,N₂⁺（B²Σ_u⁺）,and O（3p⁵P）in the dispersive discharge plasma;The larger the electrode gap is,the smaller the electric field intensity is.Therefore,the emission intensity of N₂（C³Π_u）,N₂⁺（B²Σ_u⁺）,and O（3p⁵P）in the diffuse discharge plasma decreases significantly;the higher the gas flow rate of oxygen the lower the emission intensity of N₂（C³Π_u）in the dispersive diffuse plasma;the emission intensity of N₂⁺（B²Σ_u⁺）and O（3p⁵P）is almost not affected by the gas flow rate of oxygen.（3）The temperature and reduced electric field of an atmospheric pressure diffuse discharge plasma.The vibrational temperature and rotational temperature of N₂（C³Π_u）in the plasma were calculated by Specair software using a plasma generator with a floating electrode structure;The effects of applied voltage,electrode gap,and gas flow rate on the vibrational temperature and rotational temperature of N₂（C³Π_u）in the plasma are analyzed and discussed;In addition,the effects of applied voltage on R_391/337 and reduced field under different electrode gap conditions are discussed.The results show that the vibrational temperature of N₂（C³Π_u）tends to decrease slowly with the increase of applied voltage under the conditions of small electrode gap（15 mm and 20 mm）;the smaller the electrode gap the smaller the vibrational temperature of N₂（C³Π_u）;The rotational temperature of N₂（C³Π_u）tends to increase;the smaller the electrode gap the more obvious the thermal effect is,and the higher the rotational temperature of N₂（C³Π_u）;The vibrational temperature has an opposite trend to the rotational temperature with respect to the transfer between the vibrational energy and rotational energy;Under the condition of large electrode gap（25 mm）,the reduced field strength tends to increase with the increase of applied voltage.Thus,the average electron energy in the plasma rises and the vibrational temperature of N₂（C³Π_u）shows a significant upward trend;With the increase of the applied voltage,the rotational temperature of N₂（C³Π_u）does not change significantly due to the insignificant heating effect of the transient energy exchange between gas molecules and ions in the small discharge region;The vibrational temperature and rotational temperature of N₂（C³Π_u）are almost not affected by the gas flow.