Increasing the bandwidth of an extended interaction klystron at 0.34 THz by staggered tuning of the multi-gap cavities

increase the bandwidth of EIKs at 0.34 THz, a synthetical method containing several steps is proposed. As the crucial unit determining the performance of EIKs, the output cavity is studied. Based on the theory of space charge wave, the number of gaps in the output cavity is optimized to increase both the interaction efficiency and the instantaneous bandwidth. The approaches of tuning the shape of a barbell gap and the number of gaps in idler cavities are studied, leading to the practicable method of staggered tuning on all the intermediate cavities. As a result, the bandwidth of an EIK is improved step by step. Another approach of adjusting the drift tubes is also discussed and the synthetically tuning strategy for terahertz EIKs is concluded. Finally, the optimized nonuniform structure is verified by PIC simulations and the results show that it can effectively broaden the -3dB bandwidth up to 500 MHz, which is double that of the uniform structure. The synthetical method is proved to be practicable in tuning the bandwidth and capable to keep the device operating in stability. Copyright (C) EPLA, 2018