Comparative Study on the Nonlinear Theory and PIC Simulation of Confocal Gyro-TWAs

The large-signal theory, including the BEAMLETS model and averaged coupling impedance formalism, of confocal gyrotron traveling-wave amplifiers (gyro-TWAs) with diffractive loss has been derived. As an example, a $\textit{W}$ -band gyro-TWA with uniform confocal circuits and curved-profile magnetic field is theoretically studied and then well validated by three-dimensional particle-in-cell (3-D-PIC) simulation in detail. The results predicted by our code achieve excellent agreement with the PIC simulation over 92-104 GHz regarding the electron efficiency and radio frequency (RF) wave efficiency profile along the circuit position and saturation amplification performance, with a saturation input power difference of less than 20%.