Numerical simulation of the fast diffusion process of the collector plasma in the relativistic backward wave oscillator

In this paper, we analyze the diffusion process of the collector plasma in the relativistic backward wave oscillator (RBWO) by means of numerical simulation. The results show that there is a fast diffusion process of the collector plasma, corresponding to a plasma electron velocity of 20 cm/ns. In this process, the plasma affects the modulation of the intense relativistic electron beam (IREB), leads to microwave frequency drift, absorbs the microwave power on an order of GW levels, and finally causes the pulse shortening. Here, mechanism of the fast diffusion process is mainly attributed to the excessive plasma density and the standing wave pattern of microwave field in the interaction region.