To obtain uniform atmospheric pressure plasma in air, a nanosecond pulse power supply is used to excite a double layer dielectric barrier discharge (DBD) with indium tin oxide (ITO) glass as grounded electrode. The effects of pulse repetition frequency (PRF) and voltage slew rate on the discharge uniformity are investigated in the PRFs range of 500 Hz-11kHz and the rising edge time range of 50 ns-400ns with fixed applied voltage amplitude. The discharge images taken from the ITO glass side are analyzed with a digital image processing method-gray level histogram (GLH). The corresponding voltage-current waveforms are measured to reveal the effect of the electrical parameters on the discharge uniformity. The results show that when the PRF is less than 5 kHz, the discharge is uniform. With the PRF increases, the residual charged particles will lead to the deterioration of the electrical field and decrease the uniformity. The rapid voltage slew rate can increase the reduced electric field strength in space, which promotes the electron avalanche merging and increase the discharge uniformity. It is also found that the increase of PRF would lead to the increase of the peak values of the gap voltage and the discharge current first (from 500 Hz to 3 kHz) and then decrease. The increase of voltage slew rate leads the decrease of the peak values of the gap voltage and the discharge current. These results reveal that the changes of the PRF and voltage slew rate lead to the variation of the reduced electric field strength and space charge, which can be used to monitor the uniformity of air DBD.

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