Design of slow-wave structure and beam-wave interaction simulation for helix traveling-wave tube

A Ku-band helix traveling-wave tube (TWT) is designed using theoretical analysis and simulation. The effect of the variation in inner radius on dispersion and coupled impedance is analyzed to optimize the slow-wave structure of helix TWT. The input and output structure of TWT is simulated, the input reflecting coefficient is less than -19 dB and the voltage standing wave ratio (VSWR) is less than 1.24. Periodic permanent-magnetic field is used as electromagnetic focusing system, the magnetic system period is 8.5 mm and the magnetic peak value is 0.17 T. The slow-wave circuit with property of dynamic velocity tapper (DVT) is used to increase the interaction efficiency, it can provide enough time for the interaction of beam and high-frequency field and make electrons continuously transport energy to high-frequency field. The helix TWT is simulated using a three-dimensional particle-in-cell (PIC) code. The simulation results demonstrate that the output power is bigger than 88.7 W, the electron efficiency is bigger than 14.8% and the saturated gain is bigger than 34.6 dB in the frequency range from 12.5 to 16.0 GHz.