(b)
Fig 2 The complete tube with periodic dielectric-loaded structure and its output power. (a)the complete tube, (b) simulation and test.
The analysis of mode competition is an important part of the study of the performance of high-frequency interaction structures. Figure 3 shows the dispersion curves of different waveguide modes and electron cyclotron resonant curves, the dispersion curve of the working mode TE21 and the electron cyclotron resonant curve when s=2 are tangent to point C, where the tangent magnetic field Bg=5190 Gauss; At the same time, there are intersections between the dispersion curves of the TE31 and TE41 modes and the electron cyclotron resonant curves in the region of negative axis (kz<0), that are the two points A and B in the figure, which may cause return oscillation, and the corresponding starting frequency points are 36.56 GHz and 46.56 GHz, respectively. Therefore, the suppression of the main competitive mode TE31 and TE41 mode is the key to designing second harmonic TE21 gyro-TWTs.