Characteristic radiation of nitrogen under subnanosecond breakdown in a highly nonuniform electric field near the positi
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IED PHYSICS
Characteristic Radiation of Nitrogen under Subnanosecond Breakdown in a Highly Nonuniform Electric Field near the Positive-Polarity Electrode V. F. Tarasenko*, E. Kh. Baksht, A. G. Burachenko, and M. I. Lomaev Institute of High Current Electronics, Siberian Branch, Russian Academy of Sciences, Tomsk, 634055 Russia *e-mail: [email protected] Received May 12, 2016
Abstract—Results are presented from experimental studies of elevated-pressure diffuse discharge in a highly nonuniform electric field. It is shown that, in discharges in nitrogen and air, the characteristic radiation (the K-line of nitrogen) is generated at the positive polarity of the electrode with a small curvature radius. X-ray bremsstrahlung from the anode was detected in a discharge in atmospheric-pressure air at a 12-kV amplitude of the incident voltage pulse. DOI: 10.1134/S1063780X17070121
INTRODUCTION Pulsed volume (diffuse) discharges in different gases at elevated pressures have attracted considerable attention for a long time [1–3]. High-pressure volume discharges in a uniform electric field are initiated by means of an auxiliary source (an electron beam or short-wavelength radiation) creating initial electrons from which electron avalanches develop in the gap [1]. When avalanche heads are overlapped before reaching the critical size [4], a volume discharge forms in a wide range of experimental conditions. It is also well known that high-pressure diffuse discharges can form in a nonuniform electric field without using an auxiliary source of initial electrons (see [3] and references therein). Diffuse discharges can form in gaps where one electrode has a small curvature radius, while the second is planar, as well as in gaps where both electrodes have small curvature radii. By now, it has been reliably established that, at the negative polarity of the electrode with a small curvature radius, the atmospheric-pressure air filling the gap is preionized by runaway electrons generated near the cathode [5]. The number of runaway electrons generated during a subnanosecond breakdown by a negative-polarity voltage pulse can amount to 1010 and more. In a discharge in atmospheric-pressure air, ≅6 × 1010 electrons were detected behind an Al foil anode. At the full width at half-maximum (FWHM) of the current pulse of 100 ps, this corresponds to the amplitude of the runaway electron current of ≅100 A [6]. Due to the generation of runaway electrons, initial electrons are created in the gap in a number sufficient to initiate
a diffuse discharge in a wide pressure range. In particular, diffuse discharges form when the number of runaway electrons is several orders of magnitude less than the number of electrons earlier detected behind the anode foil (~1010 electrons [6]). However, the mechanism of formation of a high-pressure diffuse discharge at the positive polarity of the electrode with a small curvature radius, when runaway electrons escape onto the anode or into the dense plasma the front of which propagates toward the cathode, still remains uncl
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