Optimal Design of a Two-Section Severed Helix TWT by 3-D Numerical Simulation

We are proceeding with activities to fully implement 3-D numerical simulations in the optimum design of high-performance helix traveling-wave tubes (TWTs). In this study, we utilize 3-D electromagnetic field analysis software to model the parts that contribute to the instabilities of helix TWTs and perform a comprehensive performance analysis that considers all instabilities simultaneously. We model K-band 150 W class helix TWT currently under development and perform analysis with CST Studio Suite. The calculation result of the small signal gain (SSG) and beam efficiency agree with the measurement results with a slight error of 1.9 dB and 0.4%, respectively. We also proposed a method for designing the velocity taper in accordance with the velocity reduction of the electron beam during saturation operation. We obtained the results showing the possibility of improving the beam efficiency from 22.4% to 26.7% with the proposed method.