Experimental study on hard X-rays emitted from metre-scale negative discharges in air

TL;DR

This study examines meter-scale negative air discharges, revealing their X-ray emission characteristics, spatial distribution, and underlying mechanisms, with implications for understanding lightning leader processes.

Contribution

It provides detailed observations of X-ray emissions from negative discharges, including their timing, spectrum, and associated discharge structures, advancing knowledge of high-energy phenomena in air breakdown.

Findings

X-rays appear in nanosecond bursts near the cathode

X-ray spectrum characterized by 200 keV exponential distribution

X-ray emission correlates with encounters between streamers

Abstract

We investigate the development of meter long negative discharges and focus on their X-ray emissions. We describe appearance, timing and spatial distribution of the X-rays. They appear in bursts of nanosecond duration mostly in the cathode area. The spectrum can be characterized by an exponential function with 200 keV characteristic photon energy. With nanosecond-fast photography we took detailed images of the pre-breakdown phenomena during the time when X-rays were registered. We found bipolar discharge structures, also called "pilot systems", in the vicinity of the cathode. As in our previous study of X-rays from positive discharges, we correlate the X-ray emission with encounters between positive and negative streamers. We suggest that a similar process is responsible for X-rays generated by lightning leaders.