Experimental and theoretical studies of the spatial distribution of the ionization rate in a non-self-sustained discharg
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Experimental and Theoretical Studies of the Spatial Distribution of the Ionization Rate in a NonSelfSustained Discharge Controlled by a Fast Electron Beam V. A. Gurashvili, I. D. Dzhigailo, N. A. Dyatko, E. M. Zanozina, I. V. Kochetov, D. I. Spitsyn, and D. Yu. Tkachenko Troitsk Institute for Innovation and Fusion Research, Troitsk, Moscow oblast, 142190 Russia Received June 9, 2011
Abstract—The spatial distribution of the current density of fast electrons and the ionization rate in a gap filled with atmosphericpressure air under the conditions of a nonselfsustained discharge controlled by a fast electron beam were investigated. The experiments were carried out in a gasdischarge chamber with a grid electrode arranged in parallel to the exit window of the ionization source. Spatial variations in the current density of fast electrons resulting from the grid were measured. The propagation of the electron beam through the discharge system was simulated numerically by the Monte Carlo method in the socalled “effective col lision” approximation. The calculated results agree well with the experimental data. DOI: 10.1134/S1063780X11120038
1. INTRODUCTION
the grid electrode, because their ribs produce “shadow” regions screened from the beam electrons. The inhomogeneity of the current density of fast electrons in the GDC results in the inhomogeneity of the spatial distribution of the gas ionization rate. Note that the ionization rate depends not only on the cur rent density of fast electrons, but also on their energy, which decreases as the electrons propagate through the gasfilled gap. The passing of a fast electron beam through the “foil–gasfilled gap” system was studied in a number of papers, including those devoted to simulations of the processes occurring in the gain media of gas lasers [5–9]. The simulations were usually performed by the Monte Carlo method. Taking into account the simula tion results, a simple formula was proposed in [6] for the energy loss of fast electrons in matter per unit reduced path length. This formula is widely used to estimate the ionization rate of gas mixtures (see, e.g., [10, 11]). In all the papers cited above, a “foil–gas filled gap” system was considered; i.e., either there were no additional elements or their influence on the beam propagation was ignored [5]. Here, we present results from experimental and theoretical studies of the spatial distribution of the rate of gas ionization in a gasfilled gap by a fast electron beam in a system with a grid electrode placed in paral lel to the IS exit window.
Nonselfsustained discharge controlled by a fast electron beam is used to pump the gain medium in electronbeamsustained lasers [1–3]. The quality of the laser beam depends substantially on the homoge neity of medium excitation in the discharge volume. In turn, the excitation homogeneity depends on the spatial distribution of the rate of medium ionization by the electron beam. The fast electron beam is formed in the ionization source (IS), also called the
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