Improvement of output power in G-band EIK with optimized and tapering gap length

The influence of period on the synchronization characteristics of beam with wave is analyzed in the design of G-band extended interaction klystron (EIK). Theoretical calculation determines the initial value of period, which is verified by 3D PIC simulation. The calculation shows that the optimal synchronization period is achieved as electron velocity is slightly larger than the phase velocity of operation mode. By optimizing gap length, the electric field distribution will be much better, which is corresponding to the larger effective characteristic impedance. The peak output power can be improved with the optimized gap length from 360 W to 570 W. Furthermore, by adopting the tapering gap length, the peak output power can be extended to 660 W.