A high-efficiency C-band coaxial transit time oscillator with a dual-cavity extractor under low-magnetic fields

Abstract

A high-efficiency C-band coaxial transit time oscillator with a dual-cavity extractor under low-magnetic fields is designed and studied through small-signal theory and particle-in-cell simulation. Small-signal theory analysis indicates that a dual-cavity extractor is superior to a single-cavity extractor in terms of the beam-coupling coefficient, the resonant frequency, and the external quality factor, which are good for high efficiency. Typical simulation results of the proposed device show that an output power of 1.73 GW and a frequency of 6.37 GHz can be obtained with a diode voltage of 455 kV and current of 9.75 kA. The corresponding power efficiency reaches 39 %, and the guiding magnetic field is 0.8 T. Further simulation demonstrates that the power efficiency exceeds 34 % in a rather large range of diode voltage from 385 kV to 470 kV and can reach higher than 35 % with a low guiding magnetic field of 0.4 T. Then this coaxial transit time oscillator is compared with the typical relativistic backward wave oscillators from the magnetic field, efficiency and power saturation time.