Numerical study of an 8 mm third-harmonic peniotron with a gradual reversal of the magnetic field

Abstract

A novel large-orbit electron gun with a gradual reversal of the magnetic field for the 8 mm third-harmonic peniotron is numerically studied in this paper. In the permanent magnetic condition, an electron beam with axial velocity spread of 4.78%, guiding center deviation of 7.18%, and velocity ratio of 2.2 is generated in the gun, satisfying the special requirements of beam-wave interaction in the third-harmonic peniotron. Compared with the traditional three stage method, it is unnecessary here to generate a thin tubular electron beam before the reversal point and the mutational distribution of reversal magnetic field. In addition, the emission band can be placed in the area of axial magnetic field where its magnitude decreases gradually, which reduces the structure complexity and the difficulties in tube-making process greatly. Finally, the peniotron is predicted to yield an output power of 31.9 kW at 30 GHz, with its microwave conversion efficiency of up to 49.4%, which shows the perfect matching between its high frequency system and its electron-optical system. According to the numerical calculations, the device performance is very sensitive to the relative axial position between the magnetic system and the electrode system. If the magnetic system shifts 0.8 mm to the right, the device efficiency would decrease from 49.4% to 31.7%. This phenomenon provides meaningful information in the device hot-test.