Characterization of surface dielectric barrier discharge plasma sustained by repetitive nanosecond pulses

The present work discusses experimental characterization of a surface Dielectric Barrier Discharge (DBD) plasma sustained by repetitive, high-voltage, nanosecond duration pulses. The measurements have been conducted in quiescent room air. Current, voltage, instantaneous power, and coupled pulse energy in the surface DBD actuator powered by high voltage nanosecond pulses have been measured for different pulse peak voltages, pulse repetition rates, and actuator lengths. Pulse energy per unit length is controlled primarily by the pulse peak voltage and is not affected by the actuator length. The results show that the actuator can be scaled to a length of at least 1.5 m. Images of the plasma generated during the nanosecond pulse discharge development have been taken by an ICCD camera with nanosecond gate. The results show that the plasma remains fairly uniform in the initial phase of discharge development and becomes highly filamentary at a later stage. Although the negative polarity nanosecond pulse discharge generates uniform plasma at low pulse repetition rates (∼100 Hz), the plasma becomes strongly filamentary as the pulse repetition rate is increased beyond ∼1 kHz. Phase-locked schlieren images have been used to visualize compression waves generated by the repetitively pulsed plasma and to measure the compression wave propagation speed. Density gradient in the compression waves generated by the nanosecond pulse discharge has been inferred from the schlieren images using calibration by a pair of wedged mirrors. The results demonstrate that compression waves generated by discharge filaments have higher amplitude and higher speed, compared to those produced in a diffuse discharge. Purely rotational CARS thermometry has been used to measure the temperature in a repetitive nanosecond pulse discharge filament, stabilized by using a sharp point floating electrode. The temperature rise in the filament, inferred from the CARS measurements, approximately ΔT=40 K, is significantly lower compared to the temperature rise in the filament inferred from the UV/visible emission spectroscopy measurements at the same conditions, ΔT=350 K. Comparison of the experimental density gradient in a compression wave generated by a nanosecond pulse discharge filament with modeling calculations suggests that the temperature inferred from the emission spectroscopy is more accurate.