Effect of metal-submicron-particle accumulation on the stability of consecutive high-pulse-power breakdowns in compressed N₂

Abstract

Pulse-power technology has been widely used in inertial-confinement fusion, electron-beam accelerators, and the aeronautics and astronautics fields. However, particle contamination can reduce operational stability by altering the breakdown process. The objective of this paper is to study the effects of large numbers of metallic submicron particles on the breakdown characteristics. Particles were spontaneously generated via consecutive high-pulse-power breakdowns in compressed N2. In this paper, we adopted a plasma-diagnosis system that combines a laser scattering technique with laser shadow photography to detect particles originating from different materials. To distinguish the specific effects of particles, a double-electrode/double-pulse method was used to eliminate the unwanted effects of electrode erosion. After thousands of consecutive breakdowns, numerous particles were unexpectedly found to suspend and accumulate in the inter-electrode gap rather than fall to the bottom. These particles mainly stemmed from the anode and were identified as either metallic conducting nanoparticles or submicron particles. Furthermore, their density continuously increased and remained at a high level for a long time. This converted the insulating medium from a pure gas to a mixture with numerous metallic particles. In this case, the probability of breakdowns involving particles increased and their mean breakdown voltage showed a downward trend. According to our analysis of the field-enhancement process, these small particles alone can neither cause field emission nor trigger a microdischarge. However, their collective effects could be significant if they were involved in the breakdown channel.