Relativistic electrons from sparks in the laboratory

TL;DR

This study demonstrates the production of relativistic electrons in laboratory sparks using a high-voltage setup, providing insights into electron acceleration mechanisms relevant to natural lightning phenomena.

Contribution

It provides experimental evidence of relativistic electrons generated in meter-scale sparks and links their origin to strong electric fields near streamer clouds.

Findings

Electrons of approximately 300 keV are produced 30-60 cm from the negative electrode.

Most detected photon bursts are likely caused by relativistic electrons rather than soft photons.

The experimental results support models of electron acceleration in strong electric fields during sparks.

Abstract

Discharge experiments were carried out at the Eindhoven University of Technology in 2013. The experimental setup was designed to search for electrons produced in meter-scale sparks using a 1 MV Marx generator. Negative voltage was applied to the high voltage (HV) electrode. Five thin (1 mm) plastic detectors (5 $\rm cm^2$ each) were distributed in various configurations close to the spark gap. Earlier studies have shown (for HV negative) that X-rays are produced when a cloud of streamers is developed 30-60 cm from the negative electrode. This indicates that the electrons producing the X-rays are also accelerated at this location, that could be in the strong electric field from counterstreamers of opposite polarity. Comparing our measurements with modeling results, we find that $\sim$300 keV electrons produced about 30-60 cm from the negative electrode are the most likely source of our measurements. A statistical analysis of expected detection of photon bursts by these fiber detectors indicates that only 20%-45% of the detected bursts could be from soft ($\sim$10 keV) photons, which further supports that the majority of detected bursts are produced by relativistic electrons.