The electron runaway mechanism in dense gases and the production of high-power subnanosecond electron beams

Abstract

New insight is provided into how runaway electrons are generated in gases. It is shown that the Townsend mechanism of electron multiplication works even for strong fields, when the ionization friction of electrons can be neglected. The nonlocal electron runaway criterion proposed in the work determines the critical voltage ± pd relationship as a two-valued function universal for a given gas (p being the gas pressure, and d the electrode spacing). This relationship exhibits an additional upper branch as contrasted to the familiar Paschen's curves and divides the discharge gap into two regions: one where electrons multiply effectively, and the other which they leave without having enough time to multiply. Experiments on the production of electron beams with subnanosecond pulse duration and an amplitude of tens to hundreds of amperes at atmospheric pressure in various gases are addressed, and the creation of a nanosecond volume discharge with the high density of excitation power and without preionization of the gap by a supplementary source is discussed.

Supershort avalanche electron beams and x-ray in high-pressure nanosecond discharges

“…Investigation of SAEB generation in other gases at the atmospheric pressure confirmed the wellknown data [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20], that its amplitude is maximal at the gas diode filling with light gases (helium and hydrogen). However, we managed to increase considerably the pressure of various gases at which SAEB was recorded behind the foil.…”

“…The edge of the plasma moves from the cathode to anode. Under these conditions, as it was shown previously [3][4][5][6], a diffusion discharge is formed in the gap at the dense plasma edge formed by the heads of avalanches moving to the cathode resulting in the excess negative charge. When plasma reaches a definite size and, correspondingly, the gap between the plasma edge and anode decreases and the voltage in the spacing increases, a critical field E cr is achieved between the plasma boundary and anode and an electron beam is generated.…”

“…The main experimental results are presented in Figs.3-8 As it was determined previously [3][4][5][6], maximum parameters of SAEB are realized during formation of a volume discharge in a discharge gap. The present investigations confirmed this conclusion.…”

“…Such measurements of the beam current pulse duration gave the value less than 1 ns. Since 2003, an interest to investigation of e-beams generation in gas-filled diodes with high pressures has been rekindled (see the review [3][4][5] and papers [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20], and Refs in [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20]). In 2005, the advanced recording methods of electron beams and the use of digital oscilloscopes with wide bandwidth provided the measurements of the beam current duration with time resolution of ~ 100 ps.…”

Research of Discharge and Generation of Fast Electrons in Atmospheric Pressure Inhomogeneous Gas Media

“…The current state of this problem is described in detail in review papers [1,2]. Here we should note that the basic problem is a requirement of high E/N (E -electric field strength, N -number density of gas molecules) applying for transition of noticeable part of electrons into continuous acceleration (runaway or escape) mode.…”