Experimental study of hard X-rays emitted from meter-scale positive discharges in air

TL;DR

This study investigates the structure, evolution, and X-ray emission stages of meter-scale positive discharges in air, revealing that hard X-rays are emitted during streamer connection phases.

Contribution

It provides detailed temporal and spatial analysis of discharge development and X-ray emission in high-voltage air breakdown, using high-resolution imaging and synchronized measurements.

Findings

X-ray emission coincides with streamer connection to the grounded electrode.

Positive streamers form dense coronae before X-ray emission.

X-ray pulses are emitted during the connection of positive and negative streamers.

Abstract

We investigate structure and evolution of long positive spark breakdown; and we study at which stage pulses of hard X-rays are emitted. Positive high-voltage pulses of standardized lightning impulse wave form of about 1 MV were applied to about 1 meter of ambient air. The discharge evolution was imaged with a resolution of tens of nanoseconds with an intensified CCD camera. LaBr3(Ce+) scintillation detectors recorded the X-rays emitted during the process. The voltage and the currents on both electrodes were measured synchronously. All measurements indicate that first a large and dense corona of positive streamers emerges from the high voltage electrode. When they approach the grounded electrode, negative counter-streamers emerge there, and the emission of hard X-rays coincides with the connection of the positive streamers with the negative counter-streamers.