Effect of self-magnetic fields on the nonlinear dynamics of relativistic electron beam with virtual cathode

Abstract

The report is devoted to the results of the numerical study of the virtual cathode formation conditions in the relativistic electron beam under the influence of the self-magnetic and external axial magnetic fields. The azimuthal instability of the relativistic electron beam leading to the formation of the vortex electron structure in the system was found out. This instability is determined by the influence of the self-magnetic fields of the relativistic electron beam and it leads to the decrease of the critical value of the electron beam current (current when the non-stationary virtual cathode is formed in the drift space). The typical dependencies of the critical current on the external uniform magnetic field value were discovered. The effect of the beam thickness on the virtual cathode formation conditions was also analyzed.

Optimization of the Double-Gap Vircator with Electromagnetic Feedback in CST Particle Studio

“…One of the most important directions of research in the high power vacuum and plasma electronics is the study of the virtual cathode oscillators (vircators) which attract great attention of scientific community [1,2,3,4]. The vircator is a microwave generator whose operation is based on the virtual cathode oscillations (VC) in the electron beam with the overcritical current [5,1,3].…”

Higher harmonics generation in relativistic electron beam with virtual cathode

“…2,3,14 A possible direction for the improvement of vircator characteristics is the development and design of the new modifications of VCOs that use newly discovered effects occurring in the relativistic and ultrarelativistic electron beams with overcritical currents. 10,16,23,24 A promising way to increase the radiation frequency of a vircator system up to sub-THz range is the use of the higher harmonics of the fundamental frequency of VCOs in the strongly nonlinear regime of a VCO operation. Currently, a generation at higher harmonics is widely applied in gyrotrons.…”

“…Analyzing relativistic vircators, it is necessary to take into account effects being insignificant for the weakly relativistic systems, in particular, the influence of the selfmagnetic fields of a REB. 10,24 For that reason, the 3D fully electromagnetic self-consistent CST Particle Studio package is used in our work for the accurate numerical investigations of generation processes in the relativistic vircator model. In this paper, we report the results of the 3D numerical study of higher harmonics generation processes in the relativistic vircator model with the annular REB in the presence of external uniform axial magnetic field.…”

“…Note, the critical current is known to be the function of the magnetic field induction B 0 . 24,32,33 With the growth of beam current the relativistic vircator system goes into the supercritical regime, and the spectral component at the frequency of x VCO (f VCO % 21:7 GHz for the case shown in Fig. 1(a)) with satellites appear in the spectrum of current oscillations, which are characterized by the significant chaotic dynamics (see frame in Fig.…”

“…Let us introduce the normalized parameter of current supercriticality dIðB 0 Þ ¼ I 0 =I cr ðB 0 Þ determined by the ratio of the certain fixed REB current I 0 to the beam critical (space-charge limited) current I cr ðB 0 Þ. 24,35 The supercriticality parameter dIðB 0 Þ characterizes the degree of development of VC oscillations in an electron beam and depends (for the fixed beam current I 0 ) on a magnetic field induction value, B 0 . We have found out that the observed VC dynamics at the x d p frequency is developed for the relatively small values of the supercriticality parameter: from dIðB 0 Þ < 1:1 for the weak magnetic fields B 0 < 0:1 T to dIðB 0 Þ < 2:5 for B 0 > 0:5 T.…”