Linear theory of large-orbit gyrotron traveling wave amplifiers with misaligned electron beam

A linear theory of large-orbit gyrotron traveling wave amplifiers (gyro-TWAs), which can be applied to analyze the effect of electron beam misalignment, is developed by specializing the corresponding theory of small-orbit gyro-TWAs. The linear theory is validated by comparing with a nonlinear theory. Numerical results show that beam misalignment can reduce linear gain and amplification bandwidth of large-orbit gyro-TWAs and increase the starting length of large-orbit gyro-BWOs for modes in accordance with the mode-selective condition. In addition, beam misalignment can also break the limitation of mode-selective condition and make the instability problem more complex.