Spatial, temporal, and spectral characteristics of the x-ray emissions in the peripheral direction of a laboratory atmospheric discharge.

Abstract

Comprehensive measurements of the x-ray emissions in the peripheral direction of extended high-voltage discharges in 55-cm open air gaps are performed at voltages up to 1 MV. The data on the spatial, temporal, and spectral characteristics of x rays are obtained. We demonstrate that the emission of photons with energies within 5-17 keV predominates throughout the entire discharge gap. The generation of photons with energies of hundreds of keV (but not higher than 300 keV) is found to be characteristic of the cathode, near-cathode, anode, and near-anode regions of the discharge, whereas approximately in the midgap low-energy photons are primarily observed. By using nanosecond imaging, it is discovered that the x-ray generation can start almost synchronously throughout the entire discharge gap, tens of nanoseconds after the first interactions of the counterstreamers with the cathode. The very first x rays are detected during the discharge development stage, when a complex net of numerous plasma structures already formed in the gap, and the discharge prebreakdown current and voltage are of 500 A and 1 MV. In a single x-ray flash, high-energy photons are found to emerge with a 20-60 ns delay relative to the onset of the low-energy photon emission. The observed phenomena and possible x-ray generation mechanisms are analyzed.