Analytical and PIC Simulation Studies of a Megawatt Class Gyrotwystron Amplifier

In this paper, the analytical and particle-in-cell (PIC) simulation studies of an X-band megawatt class gyrotwystron have been presented. The device employs a tapered output waveguide to achieve stability against self-start oscillations due to azimuthally asymmetric modes, including the fundamental harmonic TE
₁₁
and TE
₂₁
. A full nonlinear self-consistent, single particle, multimode, and multiharmonic, transient code has been developed to study the beam-wave interaction behavior. Furthermore, the device is simulated for studying its transient behavior using a commercial PIC code “CST Particle Studio.” This predicts the saturated RF power of ~20 MW in the fundamental TE
₀₁
mode and ~1 MW in the TE
₀₂
(s = 2) mode, which is a self-generated spurious oscillation in the output section. The saturated gain is calculated as ~24 dB with a power conversion efficiency of ~20% for a relativistic electron beam having 7% axial velocity spread.