Stability Study in Dielectric Ring Loaded Periodic Interaction Structure for a Megawatt Class Gyrotwystron

In this paper, the stability and design studies of an X-band gyrotwystron using a distributed loss technique at its output waveguide section are presented. The periodic dielectric loading (PDL) in the output section of the amplifier suppresses the self-generated backward-wave parasites including TE
₁₁
, TE
₂₁
, and second harmonic TE
₀₂
modes. These parasites are investigated using the small-signal linear theory. The PDL technique improves not only the stability of the amplifier but also its gain. The PDL waveguide provides a transmission loss of 0.63 dB/cm to the desired TE
₀₁
operating mode at 10 GHz that is good enough to stabilize the operation of gyrotwystron against parasites. The nonlinear simulation predicted an RF output power of ~ 25 MW in the TE
₀₁
mode for the dc beam of 220 A, 440 kV.