Simulation of a 1-THz Complex Cavity Gyrotron With a Magnetic Cusp Gun

In this article, a 1-THz fourth harmonic complex cavity gyrotron with the magnetic cusp gun (MCG) has been investigated theoretically with the self-consistent nonlinear theory. The self-consistent nonlinear theory is composed of the electron motion equation and the electron excitation equation, which could accurately describe the interaction process between the electron beam and electromagnetic wave. The MCG is optimized to generate a large-orbit beam (LOB), and the complex cavity is designed to suppress parasitic modes and improve the output efficiency. The complex cavity gyrotron is optimized to operate at a frequency of 1-THz, achieving an output efficiency of 1% and an output power of 0.5 kW when the beam voltage is 59 kV, the beam current is 0.8 A, and the magnetic field is 9.9 T. The effects of the beam voltage, the beam current, and the pitch factor of the electron beam on the output efficiency are analyzed. Results show that when the beam voltage varies between 57 and 61 kV, the beam current between 0.3 and 1.2 A, and the pitch factor between 1.05 and 1.5, the output efficiency of the gyrotron is maintained above 0.7%. The effects of the beam quality, including the velocity spread and the beam thickness on the output efficiency, are discussed as well. Meanwhile, the effects of machining errors including structure changes of the complex cavity gyrotron and the eccentricity angle of the cathode in MCG on the output efficiency are discussed.