Investigation on accelerating the building up of oscillation and achieving a rapid startup in powerful relativistic backward wave oscillator by injecting a weak external backward signal is carried out in this paper. Synchronizing the signal with the backward wave excited by intense electron beam extracting with slow wave structure, the initial noise is greatly reduced and mode competition is restrained. The analysis is demonstrated by high power X-band backward wave oscillator experiment, in which a plasma switch is designed to realize the backward signal injection. The results show that the significant reduction of microwave output delay is attained and the start time of oscillation is ahead of 10 ns with the energy conversion efficiency increases about 62%.
The breakdown at the dielectric window of the high-power microwave (HPM) horn limits the maximum radiation power of HPM system, and keeps the bottle neck of the development of the HPM technology in decades. In this paper, the multi-way diagnostics for the window breakdown at vacuum/dielectric interface are studied in the C-band multi-gigawatt HPM experiment with the atmospheric pressure SF6 environment. The method of using the fluorinated periodic surface is demonstrated to significantly improve the power capacity by fourfold, compared with the flat surface. The threshold for fluorinated periodic surface could be higher than 70 kV/cm for HPM with the frequency 4.3 GHz, and 40 ns pulse width.
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