Numerical simulations of an antenna-amplifier-Cherenkov maser with a rod slow-wave structure operating in a non-axisymmetric mode

Abstract

It has been recently proposed that a traveling wave tube could be combined with a surface wave antenna if a relativistic electron beam propagates near and along the antenna's slow-wave structure, i.e., the TWT rf drive would simultaneously serve as the antenna feed signal. In the simplest geometry of such an antenna-amplifier, an annular beam propagates outside a dielectric rod antenna, and the drive signal is in the fundamental non-axisymmetric HE/sub 11/ mode. We present the first antenna-amplifier simulation results obtained using the 3-D version of the MAGIC particle-in-cell (PIC) code. Gain and beam bunching have been demonstrated for an X-band signal entering into the system in the TE/sub 11/, mode of a circular waveguide. The linear amplifier response was observed as well as saturation at increased interaction length. In addition, the effects of the generation of harmonics of the main frequency, found earlier in one-dimensional modeling, have been verified. Furthermore, the possibility of controlling the harmonic content in the output spectrum by means of input frequency variation, also studied earlier in 1-D simulations, has been confirmed. As the frequency changes within the amplification band, the output power remains the same, and spectral peaks shift to the new frequency and its harmonics, but the harmonic content in the spectrum changes significantly.