GW-Level Ku-Band Compact Coaxial TTO With Permanent Magnet Packaging Potential

When the O-type high-power microwave (HPM) sources are extended to the high band, the current density of the intense relativistic electron beam will increase, which requires a higher intensity of the guiding magnetic field. The coil of the excitation system will be bulkier, which is not conducive to the development of the device toward the direction of light and small. The transit time oscillator (TTO) has attracted much attention due to its ability to output GW-level HPMs in the small number of cavities. In order to replace solenoid with permanent magnet, the compact coaxial TTO with a low magnetic field is designed in this article. The coaxial structure reduces the need for magnetic field strength. In addition, the familiar reflector is removed and the axial size of the beam-wave interaction region is reduced, which not only reduces the risk of electron beam diffusion under low magnetic field, but helps to reduce the weight of permanent magnets in the future. In particle-in-cell (PIC) simulation, the proposed coaxial TTO can output more than HPMs of 1.0 GW under the magnetic field less than 0.4 T with the efficiency is over 30%. Therefore, it is feasible to use permanent magnet packaging for the device.