Experimental study of hard x-rays emitted from metre-scale positive discharges in air

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. LaBr 3 (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. Leaders are seen to form only at later stages.

Energy Distribution of X-rays Produced by Meter-Long Negative Discharges in Air

“…The two types of distributions considered produce similar results for the mean energy and for the total number of photons. Despite being slightly different from previous estimates reported in [7,[13][14][15][16], the values derived in this study are of the same order of magnitude as these previous estimates.…”

“…Even though the negative discharge development was simplified in the model, the main idea that the streamer encounters can cause X-ray emissions has been supported by recent experimental observations. In the case of positive breakdown in the laboratory, X-rays indeed appear when the positive streamers from the high voltage electrode meet the negative streamer that originates from the ground [7]. In recent studies, X-ray emissions were observed during the initiation of negative leaders from the high voltage electrode [9].…”

“…It is now a well observed fact that electrical discharges produce high energetic radiation from very soft X-rays in few kilo electron volts up to X-rays and gamma rays having several mega electron volts (Moore et al [1]; Dwyer et al [2,3]; Rahman et al [4]; Nguyen et al [5]; March and Montanyà, [6]; Kochkin et al [7]). Experiments show that not only lightning flashes but also laboratory discharges generate X-rays (as first shown by Dwyer et al [3]).…”

Atmospheric Electrification in Dusty, Reactive Gases in the Solar System and Beyond

“…The Fermi Gamma-Ray Space Telescope detected a clear positron annihilation signal over Egypt from a thunderstorm over Zambia where the two events were connected in space and time through a geomagnetic field line (that electrons and positrons follow sufficiently high in the ionosphere where collisions with air molecules are negligible; Briggs et al 2011). High-energy X-rays were also detected from lightning leaders approaching ground and from long sparks in the laboratory, see, e.g., Kochkin et al (2012). We refer to the review by Dwyer and Uman (2014).…”

X-rays and microwave RF power from high voltage laboratory sparks

“…The recent discoveries of the Terrestrial Gamma ray Flashes (TGF) by Fishman et al [1994] and the high-energy emissions produced by lightning [Moore et al, 2001] promoted the interest of the atmospheric electricity community in the high energy emissions produced by laboratory discharges at air [e.g. Dwyer et al, 2005;Nguyen et al, 2008;Rahman et al, 2008;Montanyà, 2010 and2011;Kochkin et al,2012]. One of the interests in high voltage experiments is to understand the mechanisms of the production of energetic radiation that occurs in lightning and may probably share similar properties than the intense TGF to space.…”