Evolution of the uniformity in the repetitive unipolar nanosecond-pulse dielectric barrier discharge

Abstract

The time evolution of dielectric barrier discharge driven by nanosecond pulse high-voltage power is investigated by high-speed video analysis, electrical measurements and spectral diagnostics. It is found that the discharge mode generally goes through the evolution process of filamentary discharge → diffuse discharge → filamentary discharge with the increase in discharge cycle. The time-dependent changes in the standard deviation of image gray levels indicate that the discharge uniformity first improves and then deteriorates in this evolution process. The different pre-ionization density and modulated distribution of space charges and surface charges are considered to be the main reasons for the time evolution of discharge uniformity. In addition, the experiments under different frequencies and voltages show that the transition of the discharge mode is more likely to occur at higher frequency and higher voltage. Further measurement and calculation reveal that the discharge at high frequency and high voltage has the same characteristics, that is, high pre-ionization degree, thick filament diameter and short time lag. These characteristics usually lead to higher seed electron density, larger critical avalanche size and weaker lateral inhibition effect, which make the discharge mode transition more likely to occur.

Effect of airflow on the discharge uniformity at different cycles in the repetitive unipolar nanosecond‐pulsed dielectric barrier discharge

“…The low preionization [50,51] and reduced E/N (N increases with decreasing gas temperature) caused by the heat displacement effect produce filaments with small diameter. At a higher voltage of 34.5 kV, the preionization degree increases, [27] but it is still not enough to produce a diffuse discharge in the whole space. Under the transport effect of the airflow, the concentration of the MD remnants and the preionization degree become higher in the downstream region than in the upstream region.…”

“…At higher frequencies of 1000 and 1200 Hz, the shortened discharge time interval promotes the accumulation of charged particles and heating, resulting in an increased preionization degree and thermal instability. [27,[52][53][54] As a result, filaments with large diameter are generated. After the introduction of airflow, the hot gas can be conducted away, which suppresses the thermal instability.…”

“…This trigger method has been described in detail in the previous work. [27] In the experiment, the airflow is first introduced into the space and then the discharge is turned on after the airflow velocity reaches a stable value.…”

“…The standard deviation of the image gray levels then decreases sharply to about 10, indicating the presence of a diffuse discharge with good uniformity. [27] The diffuse discharge can only be maintained for less than 20 cycles, after which the standard deviation of the image gray levels increases. The standard deviation of the image gray levels finally reaches a stable value of about 18, implying that the discharge returns to nonuniform filamentary mode after more than 40 discharge cycles.…”

“…[22,23] In fact, previous studies have shown that even for NPDBD, large-area diffuse discharges can only be stably generated and maintained at an air gap of 2-3.5 mm. [24][25][26] At larger air gap of 5 mm, [27] although diffuse discharges can occur under appropriate conditions, they will inevitably be replaced by filamentary discharges again after tens of NP cycles when strong thermal instabilities and lateral inhibition develop. Accordingly, the NPDBD under large air gap is usually in filamentary mode, when the discharge reaches a stable state.…”