Design and Experimental Demonstration of a Circular Beam Electron Gun and a PPM System for D-Band TWTs

In this article, we present a design scheme of an electron-optical system (EOS) for terahertz vacuum electron amplifiers. The performance characteristics are studied by simulation, and the feasibility is verified by transmission experiment. Based on the Pierce design method, an electron gun with an isolated beam focus electrode (BFE) is designed, which has been simulated and confirmed by CST particle tracking solver and OPERA charged particle solver. A periodic permanent magnet (PPM) system including dual D-magnets of RF signal coupling port is utilized for focusing beam transportation in the 0.15-mm-radius tunnel. The experimental results of the magnetic field are in good agreement with the simulation results. The simulation results show that the beam-focusing system with the axial peak magnetic field of 5.2 kGs can confine the electron beam within the beam tunnel. Additionally, the EOS is successfully developed and used in the
${D}$
-band folded waveguide traveling-wave tube (TWT). The experimental results of electron transmission show that the thermionic cathode with a cathode load of 5 A/cm2 can provide a beam current of 56 mA, and 90% beam current is transmitted through the beam tunnel to the collector.