The Characteristics Research on A6 Relativistic Magnetron With Diffraction Output Operating in the Negative First Harmonic of $2\pi$ /3 Mode

The characteristics of A6 relativistic magnetron with diffraction output (MDO) operating in the negative first harmonic of 2π/3-mode are studied in detail by theory analysis and particle-in-cell (PIC) simulation. By comparison with the fundamental harmonic of π-mode, it is found that the negative first harmonic of 2π/3-mode with lower phase velocity can be advantageous to improve the interaction efficiency, but its delay in the establishment is longer. Furthermore, the negative first harmonic of 2π/3-mode requires a larger axial magnetic field to satisfy the resonating condition under the same diode voltage. Therefore, the total power occupied by the MDO operating with the negative first harmonic of 2π/3-mode can be decreased in the same diode voltage condition. This can result in reduced RF power output. Employing a diode voltage of 400 kV in PIC simulation, the optimal magnetic field for the negative first harmonic of 2π/3-mode and the fundamental harmonic of π-mode are 0.51 and 0.39 T, respectively. The conversion efficiency at the negative first harmonic of 2π/3-mode is improved by 16.2%, whereas the input dc power is decreased by 1.22 GW, and the output RF power decreases 0.23 GW. Meanwhile, the oscillation delays about 3-4 ns.