对相对论返波管实验中射频击穿现象进行了分析和数值模拟研究,发现谐振反射器和慢波结构的局部场增强诱导了场致电子发射,引起了金属表面的射频击穿,通过研究分析,提出采用分布反馈式谐振反射器,并采用梯形倒角非均匀慢波结构替换正弦慢波结构的方法来抑制射频击穿.数值模拟研究表明,在微波功率2 GW时,改进后的反射器最大场强由1.4 MV/cm降低为570 kV/cm,慢波结构表面最大电场由1.1MV/cm降低到780 kV/cm.改进后的结构在二极管电压765 kV时获得了微波功率2.2 GW、脉宽45 ns的实验结果,微波功率和脉宽得到显著提升.%This paper analyzes and simulates the RF breakdown in relativistic backward wave oscillator(RBWO). The RF breakdown which occurs on the surface of resonant reflector and slow wave structure(SWS) is induced by field emission. A method is proposed for reducing the surface field intensity, which utilizes cascade feedback reflector and trapezoid SWS with chamfering. The trapezoid SWS is axially lengthened at the minimum radius place for weakening field intensity so that the power capability of RBWO is increased availably. Simulation results indicate that the field intensity reduces from 1 400 to 570 kV/cm on the cascade feedback reflector, and from 1 100 to 780 kV/cm on the trapezoid SWS. Experiment results indicate that the microwave power and the pulse duration increase. A microwave with a power of 2. 2 GW and a pulse duration of 45 ns is obtained in the experiment with the improved structure of RBWO, when the diode voltage is 765 kV.
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