The theory analysis and particle-in-cell (PIC) simulation results of a 140-GHz double confocal waveguide gyrotron traveling-wave amplifier (gyro-TWA) are presented. The mode density in a double confocal waveguide is relatively sparse, and its intrinsic diffraction loss can be against the parasitic oscillation. A high-performance input coupler is designed, and simulation results show that a wave is efficiently converted from TE01 rectangular waveguide mode into the antiphase superposition TE06 double confocal waveguide mode. From theoretical analysis and PIC simulation, when the double confocal gyro-TWA and single confocal gyro-TWA operate under the same parameters, the interaction efficiency of double confocal gyro-TWA is significantly higher than the single confocal gyro-TWA. The calculated results from the nonlinear theory agree well with those from PIC simulation. The performance of the double confocal gyro-TWA is much better than that in the single confocal gyro-TWA due to a more uniform field distribution in the double confocal gyro-TWA.

Confocal waveguides; Diffraction loss; Gyrotron traveling wave amplifiers (gyro-TWA); Interaction efficiency; Non-linear theory; Parasitic oscillations; Particle-in-cell simulations; Uniform field distributions

University of Electronic Science and Technology of China