title: Meter-scale spark X-ray spectrum statistics.
abstract: X-ray emission by sparks implies bremsstrahlung from a population of energetic electrons, but the details of this process remain a mystery. We present detailed statistical analysis of X-ray spectra detected by multiple detectors during sparks produced by 1 MV negative high-voltage pulses with 1 μs risetime. With over 900 shots, we statistically analyze the signals, assuming that the distribution of spark X-ray fluence behaves as a power law and that the energy spectrum of X-rays detectable after traversing ∼2 m of air and a thin aluminum shield is exponential. We then determine the parameters of those distributions by fitting cumulative distribution functions to the observations. The fit results match the observations very well if the mean of the exponential X-ray energy distribution is 86 ± 7 keV and the spark X-ray fluence power law distribution has index -1.29 ± 0.04 and spans at least 3 orders of magnitude in fluence.
authors.affiliation: Department of PhysicsCarthage CollegeKenoshaWisconsinUSA; Birkeland Center for Space ScienceUniversity of BergenBergenNorway.
authors.forename: B E
authors.initials: BE
authors.lastname: Carlson
authors.affiliation: Birkeland Center for Space Science University of Bergen Bergen Norway.
authors.forename: N
authors.initials: N
authors.lastname: Østgaard
authors.affiliation: Technische Universiteit Eindhoven Eindhoven Netherlands.
authors.forename: P
authors.initials: P
authors.lastname: Kochkin
authors.affiliation: Birkeland Center for Space Science University of Bergen Bergen Norway.
authors.forename: Ø
authors.initials: Ø
authors.lastname: Grondahl
authors.affiliation: Birkeland Center for Space Science University of Bergen Bergen Norway.
authors.forename: R
authors.initials: R
authors.lastname: Nisi
authors.affiliation: Department of Physics Carthage College Kenosha Wisconsin USA.
authors.forename: K
authors.initials: K
authors.lastname: Weber
authors.affiliation: Department of Physics Carthage College Kenosha Wisconsin USA.
authors.forename: Z
authors.initials: Z
authors.lastname: Scherrer
authors.affiliation: Department of Physics Carthage College Kenosha Wisconsin USA.
authors.forename: K
authors.initials: K
authors.lastname: LeCaptain
keywords: X‐ray; bremsstrahlung; lightning; spark; spectrum