# Direct observation of vacuum arc evolution with nanosecond resolution

## TL;DR

This study uses nanosecond-resolution high-speed imaging to observe vacuum arc development, revealing that the cathode primarily initiates the arc, challenging the common assumption about the anode's role.

## Contribution

The paper provides the first direct, high-resolution visualization of vacuum arc evolution, clarifying the dominant role of the cathode in arc ignition.

## Key findings

- Cathodic plasma forms before anode activity
- Anode illumination is weaker and less influential
- The conductive channel develops primarily from the cathode

## Abstract

Sufficiently high voltage applied between two metal electrodes, even in ultra high vacuum conditions, results in an inevitable discharge that lights up the entire gap, opening a conductive channel through the vacuum and parasitically consuming large amounts of energy. Despite many efforts to understand the processes that lead to this phenomenon, known as vacuum arc, there is still no consensus regarding the role of each electrode in the evolution of such a momentous process as lightning. Employing a high-speed camera, we capture the entire lightning process step-by-step with a nanosecond resolution and find which of the two electrodes holds the main responsibility for igniting the arc. The light that gradually expands from the positively charged electrode (anode), often is assumed to play the main role in the formation of a vacuum arc. However, both the nanosecond-resolution images of vacuum arc evolution and the corresponding theoretical calculations agree that the conductive channel between the electrodes is built in the form of cathodic plasma long before any significant activity develops in the anode. We show evidently that the anode illumination is weaker and plays a minor role in igniting and maintaining the conductive channel.