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

This is the authors' abstract. We don't add key points for this paper.

We investigate the development of metre 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.