Study on the Mechanism of Microparticle-Initiated Breakdown in the Air Gap

The microparticle-initiated breakdown plays a key role in the failure of gas switches and has become an active area of investigation in gas discharge recently. The mechanism of the microparticle-initiated breakdown in a 2-mm air gap is studied by experiments and simulations in this article. The dynamics of the microparticle in the electric field is obtained, and four breakdown modes are acquired from the picture of the high-speed camera. The probabilities of breakdown for the 200-, 300-, and 500- $\mu \text{m}$ Cu microparticles under different voltages are presented, and the corresponding lowest breakdown voltages reduce to 65%, 56%, and 47% of the static-breakdown voltage. The relation between the breakdown voltage and position of the microparticle is calculated based on the Townsend theory. The simulated results agree well with the experimental results. The breakdown process and evolution of the plasma are also revealed with PIC simulations.