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 ${W}$ -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%.