Study On Breakdown Characteristics Of Air Discharge Under Submillimeter Gap Needle-Plate Electrode

With the continuous development of micro devices,the gas discharge problem of micro-gap is gradually becoming a bottleneck problem that restricts the performance improvement of these devices.Micro-discharge is a form of gas discharge in which the discharge is confined within a limited space,and the electrode gap or electrode size is of sub-millimeter and below magnitude.When the electrode spacing is sub-millimeter,the discharge is in the transition state from general long gap to micro-gap,and the mechanism of the discharge is not completely clear.Therefore,this thesis investigates submillimeter scale air discharges by means of experiments and numerical simulations.A needle-plate electrode discharge system for sub-millimeter gaps（100-500μm）was constructed to analyze the effects of electrode spacing and externally applied supply voltage on the discharge characteristics,and it was found that the discharge bifurcation phenomenon was not easy to occur under sub-millimeter gaps,but the discharge degree was gradually intense with the increase of supply voltage.The experiments of discharge pulse show that the pulse current amplitude of different discharge pulse periods increases and then decreases with the increase of supply voltage,and the recovery time of discharge voltage pulse and the amplitude of discharge current pulse keep the same trend;the experiments of discharge under different air pressure show that the discharge phenomenon under the same voltage becomes more intense with the decrease of air pressure,and when the supply voltage is a certain value,the decrease of air pressure.When the supply voltage is a certain value,the decrease of air pressure can also make the waveform of the discharge pulse change in different periods;Spectroscopic experiments show that during the formation of the initial discharge pulse,the peak range of the spectral line is mainly concentrated in the N₂ second positive band system（C³∏_g→B³∏_g）band at 280-460nm;With the rise of the externally applied power supply voltage,when the pulse develops to the period of repeated discharge pulses,the spectral band range extends to 280-900nm,and the change at the first N₂ positive band system（B³∏_g→A ³∑_u⁺）band of 500-900nm is more obvious,indicating that the microscopic discharge process changes at this time.During the pressurization process,the relative light intensity of the spectral lines always increases,while the electron excitation temperature shows a trend of first increasing and then decreasing.To investigate the microphysical process of submillimeter gap air discharge breakdown,a hydrodynamic model applicable to the study of submillimeter gap breakdown discharge is established using COMSOL finite element simulation software,and the simulation parameters are compared with those in experiments to verify the reliability of the simulation model.The model is used to simulate the motion process of charged particles（electrons,positive ions,negative ions）,the dynamics of spatial distribution of particles and the process of electric field and potential changes at different moments during the discharge of submillimeter gap,and to explain the discharge breakdown process of submillimeter gap from the microscopic perspective.According to the validated submillimeter gap air discharge simulation model,the effects of different factors on the discharge microphysical process are analyzed by changing the electrode shape,air pressure and secondary electron emission coefficientγ.It is found that an increase in the radius of curvature of the electrode tip will lead to a decrease in the electric field strength near the electrode tip,which results in a decrease in the rate of discharge development;when the discharge conditions are the same,the electron density,electron energy and electric field strength all maintain a consistent trend of change,increasing with the decrease in air pressure;an increase in the secondary electron emission coefficientγleads to an increase in both electric field strength and current density.