Study of the formation of a fast electron beam in a coaxial gas diode in the unlimited emission model
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IN PLASMA
Study of the Formation of a Fast Electron Beam in a Coaxial Gas Diode in the Unlimited Emission Model A. A. Grishkov, K. P. Artemov, S. Ya. Belomytsev, V. V. Ryzhov, I. Yu. Turchanovskiі, and V. A. Shklyaev Institute of High Current Electronics, Siberian Branch, Russian Academy of Sciences, Akademicheskiі pr. 2/3, Tomsk, 634055 Russia Received June 11, 2008; in final form, February 10, 2009
Abstract—The formation of a fast electron beam in a coaxial gas diode is simulated using the OOPIC Pro particleincell code under the assumption of unlimited cathode emissivity. It is shown that fast electrons are generated near the cathode. The socalled “contractingcapacitor” mechanism of electron acceleration does not operate in the parameter range under study, because the boundary of the dense plasma is spread out due to preionization of the electrode gap by fast electrons. PACS numbers: 52.25.Tx, 52.40.Mj DOI: 10.1134/S1063780X09090062
1. INTRODUCTION
2. NUMERICAL MODEL
In recent years, the problem of generation of sub nanosecond fast electron beams in highpressure gases has attracted renewed interest of theoreticians and experimentalists [1−8]. It has been shown experimen tally [1] that, when a subnanosecond highvoltage pulse is applied to an atmosphericpressure gasfilled diode with a highly inhomogeneous field near the cathode, a beam of runaway electrons with a duration of less than 50 ps is generated in the cathode region. Here, by runaway electrons (which may be emitted from the cathode or generated due to gas ionization), we mean electrons that gain more energy in the elec tric field than they lose in inelastic collisions [9].
The formation of a fast electron beam in a gasfilled diode was studied using the OOPIC Pro twodimen sional electromagnetic particleincell code [10]. This code has already been successfully used to simulate plasma and gasdischarge processes. The code is based on wellknown numerical methods: the electromag netic fields are calculated using finitedifference ana logs of Maxwell’s equations, and electron−atomic col lisions are simulated using the Monte Carlo method with allowance for elastic electron scattering and the excitation and single ionization of gas atoms by elec trons in a wide energy range.
According to the concept proposed in [2], the major role in the generation of runaway electrons is played by field emission from microprotrusions on the cathode surface. The runaway beam begins to form just after applying the highvoltage pulse and contin ues up to the start of explosive electron emission from the cathode. In this case, the beam duration is limited by a time interval of ~10 ps, during which field emis sion passes over to explosive emission. In contrast to this concept, we will consider the formation of an electron beam in the regime of unlimited electron emission and its subsequent propagation in a gasfilled diode, in which the beam current may be enhanced due to the runaway effect in plasma [3]. In the present paper, the generation of an electron
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