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By using a ballast resistor having resistance of 10 MΩ, varying the gap distance from 23 mm to 0 mm and using a fixed dc voltage at 14 kV, the streamer corona, single filament, transient glow, dc glow, and spark modes and their transitions are demonstrated in positive needle-to-plate air discharge at atmospheric pressure. The electrical characteristics, the rotational temperature, and vibrational temperature of N2, as well as the temporal behavior of streamer propagation in these discharge modes, are investigated. First, to the best of our knowledge, the transient glow mode between the single filament mode and the dc glow mode, operated in a stable repetitive fashion, is reported for the first time in positive dc air discharges. The pulse repetition frequency ranges from 7.5 to 15 kHz. The current density and the rotational temperature are in the range of 27–105 A/mm2 and 600–850 K, respectively. Its temporal behavior reveals that after the primary streamer arrives at the cathode, the secondary streamer initiates within several nanoseconds near the anode and then propagates at a high speed of 105–106 m/s. There is no transition to spark even after the secondary streamer arrives at the cathode. Second, the transition from single filament to transient glow is characterized by the sudden decrease in the pulse repetition frequency and the abrupt increase in the current amplitude, the pulse width, and the gas temperature. Third, the transition from transient glow to dc glow is identified visibly by the formation of typical glow structure (positive column, Faraday dark space, and negative glow), which is accompanied by the transition of the discharge current from nanosecond pulse to dc. In addition, both the ballast resistor and the stray capacitor exert significant influence on the transition of discharge modes.

The influences of the angle of the V‐shaped electrode, the interelectrode distance, the thickness and the types of dielectric plate on the breakdown characteristics of air coplanar dielectric barrier discharge are investigated. When the angle of the electrode increases, the ignition voltage surprisingly decreases, while both the discharge current, and plasma area remain constant. With smaller interelectrode distance or thinner dielectric plate, lower ignition voltage is required. However, if either one of the them exceeds the threshold value, the discharge mode transits from steady to stochastic. In addition, the discharge appearance in the case of alumina is visually more diffuse with respect to the cases of mica and quartz, which may be caused by the surface charges with high density.

In this work, a typical pin-to-pin plasma synthetic jet in static air is excited by a pulsed DC power supply. The influences of the pulse rising time, the amplitude and the repetition frequency of the pulse voltage on the jet flow have been investigated. First, using a high-speed Schlieren imaging technique, the induced shock waves and the fast jet flow generated by the plasma synthetic jet are characterized. With a deposited energy of 44 mJ per pulse, the velocity of the shock wave and the maximum velocity of the jet flow reach 320 m s −1 and 100 m s −1 , respectively. Second, when the applied voltage increases from 12.8 kV to 16 kV, the maximum jet velocity increases from 66 m s −1 to 93 m s −1 . On the other hand, as the pulse rising time varies from 50 ns to 500 ns, or the pulse repetition frequency increases from 5 Hz to 40 Hz, the jet velocity induced by the plasma synthetic jet is weakly dependent. In addition, a comparative study of the plasma synthetic jets using three commercial pulsed power supplies (XJ-15, NPG-18, and PG-30) is implemented. It reveals that the maximum jet velocity of 120 m s −1 is obtained in the case of PG-30, with the longest pulse rising time and the lowest breakdown voltage, while the maximum velocity of 33 m s −1 is detected in the case of NPG-18, even though it has the shortest pulse rising time and the highest breakdown voltage.

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