Microwave generation power in a nonrelativistic electron beam with virtual cathode in a retarding electric field

Abstract

Electron-wave systems with the active medium in the form of an electron beam with a virtual cathode (VC) are among the promising sources of high-power microwave radiation [1][2][3][4] and are extensively studied in the context of various applications [5,6].Recently [7][8][9], we proposed and studied a new scheme of the oscillator with a VC (vircator) making use of an intense nonrelativistic electron beam (i.e., a beam with a microperveance p µ > 3 µ A/V 3/2 [10]). In order to form a VC in the electron beam, this system employs a scheme with an additional retardation of electrons. According to this scheme (called a low-voltage vircator), a nonstationary oscillating VC is formed at the expense of strong retardation of electrons in the drift region, which makes possible the generation of both single-frequency and broadband microwave signals using electron beams with small total currents and low densities [7]. In such regimes, it is possible to study in much detail the physical processes in electron beams with VCs. It should be noted that the system with a VC and a retarded electron beam is also of interest as a controlled source of medium-power broadband chaotic signals in the centimeter and millimeter wavelength range [8].This Letter presents the results of an experimental and theoretical investigation of the output energy characteristics of a low-voltage vircator.The experimental investigation of oscillations in the electron beam with a VC was performed using as diode scheme in which the beam formed by an electron-optical system (EOS) was injected into a system (see Fig. 1) comprising two grid electrodes ( 5 and 6 ) forming a retarding field. The retarding field was created by applying a negative potential V r to the exit (second) grid 6 relative to the entrance (first) grid 5 . The EOS formed an axisymmetric converging cylindrical electron beam 4 . The accelerating voltage in our experiments was 2.0 kV, the beam current at the EOS output was varied within 50-100 mA (depending on the cathode filament voltage), the EOS length was l = 70 mm, and the beam radius was r b = 4 mm.The electron beam generated in the EOS with a certain initial scatter of electron velocities enters into the space between grids (diode gap). The first grid poten-Abstract -The power of microwave generation in a nonrelativistic electron beam with virtual cathode formed in a static retarding electric field (low-voltage vircator system) has been studied experimentally and by means of numerical simulation within the framework of a one-dimensional theory. The limits of applicability of the one-dimensional theory have been experimentally determined. 1 2 3 4 5 6 7 8 9 10 VC V 0 V r Fig. 1. Schematic diagram of the experimental setup used for the investigation of oscillations in a nonrelativistic electron beam with virtual cathode formed in a system with additional retardation of electrons: ( 1 ) thermionic cathode;( 2 ) grid electrode of the electron gun;( 3 ) second anode of the electron gun; ( 4 ) converging electron beam formed by the EOS; ( 5 ) e...

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