Long-pulse high-efficiency relativistic Cherenkov oscillators at L- and S- bands

Relativistic backward wave oscillators (RBWOs) are one type of the promising devices that can produce high power microwaves (HPMs) and is extensively investigated because of its merits such as compact structure, high efficiency, and good stability. In L-, S-, C-, and X-bands, RBWOs had achieved output power of 2-6.5 GW, efficiency of 20%-36%, and repetition rate of 20-100 Hz. However, the pulse duration of RBWOs usually does not exceed 20-30 ns owing to the “pulse shortening” phenomenon. Recently, many studies on measures restraining pulse shortening are taken to prolong the microwave pulse duration. In 2008, the Institute of High Current Electronics, Russian Academy of Sciences reported the experimental results that they had gotten a microwave with power of 3 GW and pulse duration of 90 ns in an S-band RBWO. Compared with the diode voltage pulse width (300 ns), there occurred serious pulse shortening phenomenon. And there are no repetition rate experimental reports. In 2011, the National University of Defense Technology in China reported recent advances in long-pulse HPM sources with repetitive operation in S-, C-, and X-Bands. In experiments, driven by a repetitive long-pulse accelerator (the diode voltage pulse width is about 160 ns), the S-band source operated stably with output power of 1.2 GW with pulse duration of about 100 ns in 20 Hz repetition mode. The X-band source generated 1.2 GW microwave power with pulse duration of about 100 ns in the 20 Hz repetition mode. The C-band source generated HPMs with power of about 2 GW and pulse duration of about 100 ns in single-shot mode. It was suggested that explosive emissions on surfaces of designed eletrodynamic structures restrained pulse duration and operation stability. But the beam-wave conversion efficiencies of the above HPM sources are all below 25%.