Experimental and theoretical investigation into the effect of the electron velocity distribution on chaotic oscillations in an electron beam under virtual cathode formation conditions

Abstract

-The effect of the electron transverse and longitudinal velocity spread at the entrance to the interaction space on wide-band chaotic oscillations in intense multiple-velocity beams is studied theoretically and numerically under the conditions of formation of a virtual cathode. It is found that an increase in the electron velocity spread causes chaotization of virtual cathode oscillations. An insight into physical processes taking place in a virtual-cathode multiple-velocity beam is gained by numerical simulation. The chaotization of the oscillations is shown to be associated with additional electron structures, which were separated out by constructing charged particle distribution functions.PACS numbers: 05.45.-a, 41.75.Fr

The processes of formation and nonstationary dynamics of a virtual cathode in a nonrelativistic electron beam in the decelerating field (two-dimensional approximation)

“…The results of numerical simulation were confirmed by an experimental study of the dynamics of a nonrelativistic electron beam in the decelerating field using the model of the studied system on a dismountable vacuum setup (the experimental setup and the conditions and technique of the experiment are discussed in more detail in [18][19][20]). The parameters of the experimental model were as follows: electron-beam radius R b = 4 mm, electron-beam current I 0 = 150 mA, accelerating voltage V 0 = 2 kV, transit-channel radius R c = 15 mm, and system length L = 100 mm.…”

“…The formation of a potential well in the VC region leads to the fact that the motion of electrons along the longitudinal and radial coordinates becomes much more complicated. The complex nonlinear motion of electrons in the region of the VC potential minimum eventually determines the nature of the output radiation of the studied system [18][19][20]. In this case, the space-charge-limited motion of electrons in the VC region close to the system axis, where the VC potential minimum is located, is simpler than the motion in the periphery of the electron beam.…”

“…The low-voltage vircator model [18][19][20] used in this paper (see Fig. 1) is a cylindrical interaction space of length L and radius R, which is bounded by a perfectly conducting surface (cylinder 4) in the transverse direction.…”

“…This case is interesting in that it admits the VC formation and microwave radiation generation for electron-beam energies much less than relativistic [18,19], which leads to a decrease in energy consumption and overall sizes and, correspondingly, ensures a higher efficiency of such devices. In this case, a low-voltage vircator [18][19][20][21] also differs in the possibility of tuning of generation regimes (from periodic to wideband chaotic oscillations) by varying the magnitude of the decelerating potential as well as the possibility of operation without the focusing magnetic field [18,19]. It is shown in [18] that the results of experimental studies of the low-voltage vircator model are in good qualitative and, in some cases, quantitative agreement with the results of a theoretical and numerical analysis of such a system within the framework of one-dimensional theory in which the motion of the beam electrons is assumed to be one-dimensional.…”

“…Such a mechanism is used in the operation of vircators and their various modifications [11,12]. The second mechanism is based on the introduction of additional deceleration of the electron flow (e.g., in a reflection triode or a low-voltage vircator [13,[18][19][20]). This case is interesting in that it admits the VC formation and microwave radiation generation for electron-beam energies much less than relativistic [18,19], which leads to a decrease in energy consumption and overall sizes and, correspondingly, ensures a higher efficiency of such devices.…”