Spectroscopic study of vacuum arc plasma expansion

Abstract

Vacuum breakdown (also known as arc or discharge) occurs when a sufficiently high electric field is applied between two electrodes in vacuum. The discharge is driven by the formation of an intensively glowing plasma at the cathode, which is followed by the ignition of an anode flare that gradually expands and fills the gap. Although it has been shown that the anode electrode does not play a significant role in the breakdown initiation, the nature of the anodic glow is of paramount importance for understanding the breakdown evolution. In this work, we use time-and space-resolved spectroscopy to study the anode flare. By using different anode and cathode materials, we find that excitations from both anode and cathode ions and neutrals contribute to the anodic glow. This implies that the cathodic plasma expands towards the anode without emitting any detectable light and starts glowing only when it reaches and interacts with the anode electrode. This interaction causes the introduction of anodic species in the plasma. The latter starts producing an expanding glow which contains spectra from both the cathode and anode materials and gradually fills the gap as the plasma equilibrates. Finally, we observe that after a breakdown, cathode material deposits on the anode electrode, gradually coating it. After hundreds of breakdowns, this coating covers the anode, resulting in the decay and possible elimination of the anode material signal in the spectra.

Anodic Glow and Conductive Channel Formation in Single and Double Long Vacuum Gaps

“…By combining the light emission images with theoretical calculations, we found that the expansion of the anodic glow has no crucial effect on the formation of the conductive path, since the gap voltage drops to a low level long before the anodic glow bridges the gap. In another work involving spectroscopic observations of the anodic glow during vacuum breakdowns [21], we found the initial light emission on the anode surface may also result from the ions coming from the expanding cathode plasma, which again supported the idea that the conductive channel is mainly formed by the expanding cathode plasma.…”

“…Two specially designed vacuum interrupters were used in the experiments, with one of them being a single-break interrupter and the other being double-break. We extended the gap length from 1-5 mm in [20] and [21] to 10-30 mm for the single-break interrupter, and set the movable gap in the range of 10-20 mm in series with a fixed gap of 15 mm in the double-break interrupter. The electrode configuration for the gaps in the interrupters were all tip-to-plane.…”

Effect of the anode material on the evolution of the vacuum breakdown process

“…Therefore, the anodic glow cannot be explained by thermal evaporation due to electron bombardment of the anode and alternative mechanisms have to be investigated. In our previous work performing spectroscopic observation on the anodic glow [35], we found that both the cathode and anode materials contribute significantly in the anodic glow. This implies that the cathodic flare must reach the anode so that the atoms of the cathode material can be identified near the anode.…”

In-situ plasma treatment of Cu surfaces for reducing the generation of vacuum arc breakdowns

“…Treatment with only Ar plasma was able to remove some of the impurities on the cathode, but seemingly none on the anode. However, in our study, the primary focus was on cleaning of the cathode surface, since it is known to be more strongly associated with triggering of BDs 40,41 . The optical images before and after plasma cleaning (compare Figs.…”