Efficiency enhancement simulation of helix traveling-wave tube

2.5 dimensional(2.5 D) particle in cell simulation code MAGIC and 3 D electromagnetic simulation code HFSS were used to investigate the helix traveling wave tube(TWT) with positively negatively tapered structure for efficiency enhancement. Some key parameters to efficiency were analyzed, including high frequency parameter, non synchronous parameter, gain parameter and electron phase. A positively negatively tapered helix TWT were designed and fabricated. The results show that the measured efficiency of the tapered TWT reaches 29%, while that of the non tapered TWT is 19%. It shows the average relative error of the simulation method is about 5%．