Relativistic backward-wave oscillators: Theory and experiment

Abstract

Microwave sources based on backward-wave oscillators driven by relativistic electron beams are capable of producing high-power coherent radiation in cm and mm wavelength regime. Although there have been a number of experiments reported over the last decade on this topic, there are only a few publications providing a theoretical description of these devices. Thus, there is a need for theoretical models which can be compared in detail with the experimental data. This work is devoted to fill this need and applied to the University of Maryland backward-wave oscillator experiment. It is shown that the theoretical predictions for the threshold current to start the oscillations, the frequency characteristics, and the efficiency of the device compared favorably with the experimental data.

Quasi-optical theory of relativistic surface-wave oscillators with one-dimensional and two-dimensional periodic planar structures

“…6(a)), at a sufficiently large shift of the Cherenkov synchronism point "C" from the dispersion curve extremum point "B," a transition from the p-mode operation regime to the traditional BWO regime must take place. According to the conventional BWO model, [18][19][20][21] in the latter regime the excited field can be presented as a combination of the fundamental volume modeĈ À and its evanescent synchronous spatial harmonic. Here we describe the procedure of transformation from the surface-wave oscillator model (12) to the conventional BWO model when synchronous waveĈ þ is converted into the spatial harmonic with a negligibly small energy flux.…”

“…In the Appendix we consider the transition from the model of surface-wave oscillator operating in the p-mode regime to the canonical model of relativistic backward wave oscillator (BWO). [18][19][20][21] …”

“…In these assumptions Eq. (A7) transform to a form canonical for backward wave oscillators [18][19][20][21] …”

Experiment on the plasma-loaded backward-wave oscillator using a gas-loaded foil-less diode

“…Many authors [1][2][3][4][5][6][7][8][9][10][11][12] have focused their attention on this device for more efficient operation at high-power levels, and important results have been obtained both experimentally and theoretically. In order to further enhance the output power of microwave and the conversion efficiency of electron beam to microwave radiation, some scientists [13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29] have introduced background plasmas into the BWOs, and both theoretical and experimental results have demonstrated that the background plasmas improve the beam-waveguide interaction dramatically.…”

Overmoded GW-class surface-wave microwave oscillator

“…Based on the theory of a BWO operating near cutoff [18], the starting current of device operating with a half sinusoidal field profile [appropriate to the field distribution presented in Fig. 7(a)] is (6) where is the number of periods of structure, is the longitudinal electron velocity normalized to the speed of light, is the coupling coefficient introduced in [20], is the linear efficiency given by (7) where The starting current as a function of beam voltage is plotted in Fig. 8 for the parameters corresponding to the parameters of the optimal design.…”