Integrated Planar Five-Beam Electron Optics System for 670GHz Travelling-Wave Tube

An integrated planar five-beam electron gun combined with uniform magnetic structure is investigated in this paper for our 670GHz TWT. Firstly, the theoretical design method for Pierce-type electron gun is applied to our five-beam gun with simplification of the focus electrode and the anode to facilitate manufacture and assembly, which is characteristic with 21.3kV, 5×0.015A, and beam radius of 0.025mm. Simulation results show that the gun model performs well and is verified with stable beam characteristics. Next, a uniform magnetic focusing structure used for constraining the five-beam array with adjacent beam separation of 2mm is constructed with the peak Bz of 0.51T. The combination of simplified anode and the pole-piece achieves the optimized matching of the gun and the magnet, and the calculated magnetic field distribution of the structure is equivalent for the five beams. The pole-piece with novel stepped hole is considered in our design of the magnet system, which reduce the transverse magnetic field disturbance effectively. Simulation results show that the transmission of five-beam array up to 60mm is 100% with the maximum ripple of 23% in the designed focusing structure.