Columnar Discharge Characteristics At Atmospheric Pressure And Cathode Fall Measurement Of Glow Discharges In Dielectric Barrier Discharges In Helium

Dielectric barrier discharge (DBD) has various promising applications in industry.However, theoretical understanding is still limited. In this thesis, using electrical parametersmeasurements, and the fast photography, the columnar discharge mode, the conversion andevolution process of a columnar discharge to a glow discharge were studied. Thecharacteristics of cathode fall, and the cathode fall measurement in a dielectric barrierdischarge were also investigated.Waveforms of the applied voltage and loop current were measured and short exposuretime discharge photos were taken with ICCD to investigate the characteristics of columnardischarges, especially their conversion to glow discharges. The characteristics of glowdischarges were also discussed. The results showed that columnar discharges occurred whenthe applied voltage was high enough. Each columnar discharge exhibited a mode transitionranging from Townsend to glow discharges generated by the same discharge physics as glowdischarge.After a columnar discharge generated, a single-pulse glow discharge could beachieved when the applied voltage was adjusted to a lower voltage. As the applied voltagewas increased, a two-pulse discharge appeared. At the same time, the number of dischargecolumns increased, but the diameter of each column decreased. It is found that, with anincreasing applied voltage, the discharge became uniform gradually and turned intomulti-pulse glow discharges. The discharge current cannot be used to diagnose the dischargemode. The conversion of a columnar discharge to a glow discharge with the increasingapplied voltage is a progress that the discharge changed from a partial APGD (atmosphericpressure glow discharge) to a whole APGD.A method based on the “zero-length voltage” extrapolation is first proposed to measurecathode fall in a dielectric barrier discharge. Starting, stable, and discharge-maintainingvoltages were measured to obtain the extrapolation zero-length voltage under different valuesof gap pressure and the electrode separation. The results showed that the extrapolatedzero-length voltages for each of the starting, stable, and discharge-maintaining voltagesagreed closely. The relationship between the gap voltage (breakdown voltage and quenching voltage) and the electrode separation at different values of gap pressure was linear. Under ourexperimental conditions, the “zero-length voltage” gave a cathode fall of about185V, whichwas typical for the glow mode of the discharge. Based on the known thickness of the cathodefall region, the spatial distribution of the potential and the electric field strength in dielectricbarrier discharge in atmospheric helium is determined. The electric field strength at thecathode surface for atmospheric pressure is9.25kV/cm.