Effect of pulse width and repetition frequency on the uniformity and accumulation effect of atmospheric-pressure nanosecond pulsed DBD

Nanosecond (ns) pulse excitation is considered as a promising method to enhance atmospheric-pressure plasma chemical reactivity with good controllability and uniformity. Pulse width and pulse repetition frequency (PRF) are important parameters of pulse voltage, and have significant influences on the discharge processes within one discharge cycle or the adjacent discharges. In this paper, the uniformity and accumulation effect of discharges with different pulse widths and PRFs are investigated by experimental and numerical methods. To reveal the variation of voltage on gap (U g ), discharge current (I g ), electron density (n e ), and accumulated charges on the dielectric barrier, the measured voltage-current are separated. The results show that with increasing pulse width, on the pulse rising edge, U g and I g do not change much, but on the falling edge, U g and I g increase obviously, resulting from the dissipation of space active species. With higher U g and reduced electric field (E/n) on the falling edge, more electron avalanches would be generated, facilitating discharge uniformity, n e , and electron temperature (T e ). With further increasing the pulse width, U g on the falling edge is increased accordingly, leading to the space electric field distortion and the reduction of the uniformity. Increasing of PRF causes the increase of space residual active species, which deceases U g and I g and the discharge uniformity. The spatiotemporal evolutions of discharge are recorded by intensified charge-coupled device (ICCD) camera and one-dimensional (1D) fluid simulation is also performed to explain the roles of electric field and charge accumulation.