Simulation on the Plasma Dynamics of a Needle-Plate Barrier Discharge Packed With a Single Dielectric Bead

The packed-bed dielectric barrier discharge (DBD) is popular in plasma catalysis, whose performance is determined by plasma dynamics. In this article, the plasma dynamics have been simulated with a needle-plate DBD packed with a single bead by a particle-in-cell/Monte Carlo collision (PIC/MCC) method. Simulation results reveal that the packed DBD is composed of a positive streamer on the bead surface, a local discharge near the contact point, and a plate-surface discharge with high permittivity ( $\varepsilon)$ of the bead. After passing through the bead midpoint between the needle tip and the contact point, the streamer continues propagating on the bottom half bead surface until it meets the local discharge. In contrast, the local discharge is absent with low $\varepsilon $ . The streamer propagates vertically toward the plate after the midpoint. Compared with high $\varepsilon,n_{e},E$ , and surface streamer velocity are lower, and the plasma channel is wider with low $\varepsilon $ . For different $\varepsilon $ , the densities of $ \mathrm{N}_{2}^{+},\mathrm{O}_{\mathrm{2,}}^{+}$ and $\mathrm{O}_{2}^{-}$ follow the similar temporal trend with $n_{e}$ . The deposited charge is a positive ion on the top half bead surface and an electron on the bottom half bead surface. In addition, $n_{e}$ and $E$ increase with the increase of voltage amplitude ( $V_{a})$ . If $V_{a}$ is too low, the surface streamer stops propagating after a certain distance, which increases with the increase of $V_{a}$ . Even with low $\varepsilon $ ( $\varepsilon $ $=$ 2), the local discharge can be induced if $V_a$ is sufficiently high. All the results mentioned above reveal that both $\varepsilon $ and $V_{a}$ affect the plasma dynamics greatly.