A Compact and Lightweight Distributed Electron Beam Focusing System for an X-Band Transit-Time Oscillator

With the increasing practical demands, research on the lightweight and miniaturization of high-power microwave (HPM) sources holds significant practical importance. Building upon a distributed electron beam focusing system (DEBFS), we present a compact X-band transit-time oscillator (TTO) that achieves a remarkable reduction in guiding magnet weight, from hundreds of kilograms in conventional permanent magnet (PM) configurations to merely 5.67 kg. Addressing the characteristics of this system, which produces a low guiding magnetic field and a short uniform magnetic field region, this article conducts a detailed study on the design of the beam-wave interaction area. To enhance the efficiency of the device, methods such as incorporating a cathode focusing structure and using opening foils are proposed. Additionally, the optimal length of the modulation cavity is investigated. Particle-in-cell (PIC) simulation methods are utilized to study the microwave generation capability of the device. Under conditions of a diode voltage of 410 kV and a current of 7.0 kA, the device outputs microwave power of 1.17 GW at a frequency of 8.00 GHz, with a beam-wave conversion efficiency of approximately 40.76%. The distributed magnet is finally fabricated, and measurements are taken to verify that its magnetic field configuration is consistent with simulations. This research achieves efficient microwave output from the TTO with a guiding magnet weight of 5.67 kg, providing a novel technical approach for the miniaturization of HPM sources.