Experimental study on the influence of grain boundary on breakdown in relativistic backward wave oscillator

The presence of radio frequency (RF) breakdown seriously degrades the performance of relativistic backward wave oscillator (RBWO) and affects its lifetime. In this paper, the influence of grain boundary on RF breakdown in an X-band RBWO has been experimentally investigated. Firstly, titanium with different grain sizes has been prepared using a high-temperature annealing method before its field emission characteristics are studied by a field emission test system. The experimental results indicate that the segregation effect of the impurities at the position of the grain boundary may become more pronounced as the grain size increases, which results in a significant improvement in the field emission performance of titanium. A high-power microwave experimental platform is then set up, and the influence of the grain boundary of titanium on RF breakdown has been revealed. The shortening of the microwave pulses is more serious with the increase of the grain size, and the corresponding breakdown traces appearing in the high-frequency structures become more apparent. Therefore, developing fine-grained and single-crystal metallic materials may be an important method for suppressing RF breakdown in RBWOs.