Spectrum of fast electrons in a subnanosecond breakdown of air-filled diodes at atmospheric pressure

Abstract

In this work, the spectra of electron beams produced in air-filled diodes at atmospheric pressure were studied for different cathode designs. The feasibility of correct reconstruction of the electron beam spectrum from an experimental dependence of its attenuation factor in foils of different thicknesses was demonstrated. The electron energy distributions were calculated on minimum a priori assumptions by regularization of an ill-posed problem—a Fredholm integral equation. The spectra of a subnanosecond electron beam generated in the gas gap during the voltage pulse rise time were reconstructed and analysed. A time-of-flight spectrometer study and reconstruction of the spectrum from the data on e-beam attenuation confirmed the fact that groups of electrons with two-three characteristic energies can be generated in gas-filled diodes. In experiments, electrons of energy greater than that corresponding to the nominal voltage amplitude across the gap were detected.

Why do Electrons with “Anomalous Energies” appear in High-Pressure Gas Discharges?

“…Thus, the total yield is estimated to be 2·10 9 fast electrons per pulse. This value agrees well with typical experiment data [5,16,17].…”

“…This is clear because in our model of axisymmetric discharge all the electrons generated in the amplified field on the ionization wave front, while in real discharges only a small group of particles participate in this interaction with field wave [5].…”

“…Owing to modern experimental equipment and novel methods of experimental data analysis, it was shown that the runaway electron beams have a broadband spectrum containing several groups of electrons with different mean energies [5,6]. The main amount of runaway electrons constitutes the group of particles with mean energy corresponding to the voltage amplitude at the gap.…”

Supershort avalanche electron beam inSF6and krypton

“…Generally, the generation RAEs consists of four main stages: (i) the appearance of initial electrons, (ii) the mode transition into runaway electrons for part electrons, (iii) the generation of general RAEs, (iv) the ionization wave front arrival at the anode [1,7,13,15,19]. In the first stage, when the nanosecond high-voltage pulses are applied on the cathode, the electric field strength achieves sufficient value (>10 7 V=m) at the macro-and micro-inhomogeneities of the cathode, resulting in the appearance of initial electrons near the cathode and the development of electron avalanches.…”

“…Nevertheless, Tarasenko et al achieved some different experimental results on RAEs. It was found that there were two or three groups of electrons with different energies in the RAE beam obtained downstream from the anode foil [13][14][15]. Moreover, under an optimal condition, the quantity of electrons with the anomalous energy was not more than 10% of the total number of the RAEs.…”