The simulation has been conducted using CST-PIC to study the beam-wave interaction in the designed model of large-orbit gyro-TWT. When the electron beam velocity spread is 3.5%, by varying the power of the input signal, the output saturation power corresponding to each frequency can be obtained, and the result is shown in Figure 9, with -3dB bandwidth of 4.3 GHz, from 27 GHz to 31.3 GHz. Figure 10 shows the gain and efficiency curves, with saturation gains ranging from 37 dB to 48 dB, and efficiency between 12 and 25 percent.
Under the same working conditions, the change of output power with the electron beam velocity spread at the working frequency f=29GHz is shown in Figure 11, it can be seen that when the spread is higher than 5%, the output power begins to decrease significantly, so the velocity spread of the electron gun is best controlled within 5%. This result is close to that of the small-orbit gyro-TWTs, which means dielectric-loaded structure is more sensitive to velocity spread than the helically corrugated waveguide structure.