Theoretical Design and Numerical Simulation of Beam-Wave Interaction for $G$ -Band Unequal-Length Slots EIK With Rectangular Electron Beam

A beam-wave interaction model for G-band rectangular beam extended-interaction klystron (EIK) with unequal-length slots is proposed and analyzed to achieve high output power and broad bandwidth. The length ratio of long slot with short slot is carefully optimized to obtain a large effective characteristic impedance and wide mode separation. The influence of beam tunnel size on the effective characteristic impedance is studied with the beam aspect ratio of 2.3:1. The beam conductance for 5-gap, 7-gap, and 11-gap cavities are analyzed theoretically to optimize the beam-wave interaction stability. Furthermore, beam current and input power are investigated to obtain high performance. The analysis of fabrication tolerance and alignment tolerance indicates that less than 5μm machining precision is required. With beam current of 0.40 A and voltage of 16.5 kV, 3-D PIC simulation predicts peak power of 1139 W and 3-dB bandwidth of 1.15 GHz, with efficiency of 17.3% and gain of 37.5 dB. In addition, PIC simulations are compared with 1-D AJDISK calculations, the approximate results with similar tendencies indicate that our proposed beam-wave interaction model for G-band EIK is relatively reliable.