Numerical study of matching conditions and optimum structure of an input coupler for a 0.34-THz extended-interaction klystron

To develop a reliable and stable EIK at 0.34 THz, an analysis of the input circuit is presented and some aspects regarding the practicalities of the device are specifically discussed. The structure of the coupler is first optimized to improve the driving signal injection. The effects of gap voltage on the beam-wave interaction are studied, leading to the evaluation of the driving power needed. By analyzing the currently available seed sources and the possibility of electrical breakdown, proper input conditions are established. Finally, an optimized input circuit is shown to match well the simulation results obtained by using the particle-in-cell (PIC) method. The simulation results demonstrate that the optimized device can operate stably with a gain of 28.8 dB when the input power is matched at 7.9 mW.