Trichel Pulse Characteristics Of Negative Corona Discharge In Submillimeter Gap

Negative corona discharge is generally focused on millimeter and centimeter gaps,but few reports so far reside on negative corona discharge of sub-millimeter gaps.The negative corona discharge process of sub-millimeter gaps are distinctive from those millimeter and above gaps.The complexity of corona discharge makes its microscopic process unclear,among which Trichel pulse characteristics best represents the complex process of negative corona discharge.In the present study,we investigate Trichel pulse characteristics of negative corona discharge in submillimeter gaps,which reveals complex physical process of negative corona discharge,and will be of great significance for insulation protection of micro-electromechanical systems.Negative corona discharge system of needle-plate electrode suitable for submillimeter gaps(100-500μm)is built up to explore the characteristics of negative corona discharge Trichel pulses under different electrode spacing and tip curvature radius.Especially,optical acquisition system is used to promptly picture negative corona which is correlated to Trichel pulse current for elucidating Trichel pulse characteristics of negative corona discharge in sub-millimeter gaps.It is indicated that when the negative corona discharge in the sub-millimeter gap has developed into the discharging stage of Trichel pulse sawtooth wave,the sawtooth wave stage cannot transit to glow discharge,and the pulse waveform showed a sawtooth waveform type accompanied by the basal current,and there was no pulse-free phase.In order to investigate the microphysical process of submillimeter gap negative corona discharge,the parameter group of millimeter gap discharge is improved,and the secondary electron emission region is determined based on the corona discharge images obtained from the optical acquisition system;the submillimeter gap collision ionization coefficient is calculated,and the hydrodynamic model applicable to the submillimeter gap negative corona discharge is obtained,and the Trichel pulse simulation waveform is compared with the experimental results to verify the simulation model.The model is used to simulate the charged particle transport process,particle distribution dynamics and electric field changes at different stages of the 100μm gap Trichel pulse.The effect of the change of the tip curvature on the Trichel pulse amplitude and frequency is explained from the microscopic point of view,and it is found that the increase of the tip curvature radius decreases the electron density and positive ion density,which in turn increases the suppression effect of the negative ion cloud on the electric field intensity and decreases the Trichel pulse amplitude,which is consistent with the experimental results.The verified negative corona discharges of 100μm air-gap in needle-plate electrode model are simulated to quantitatively evaluate impact ionization coefficient α,adsorption coefficient η,secondary electron emission coefficient γ,and charged particle mobility which play a key role on Trichel pulse characteristics and are explained microscopically for negative corona discharge processes.It is indicated that both the amplitude and frequency of Trichel pulse currents are positively dependent on impact ionization coefficient α and secondary electron emission coefficient γ.The increase of adsorption coefficientη makes Trichel pulse frequency and the amplitude of Trichel pulse current decrease with the increase of the rising time.The amplitude and frequency of the Trichel pulse current are more sensitive to negative ion mobility.