Design and efficient operation of a coaxial RBWO

Abstract

Coaxial relativistic backward wave oscillator with the rippled inner conductor not only increases the output efficiency but also results in the serious phenomenon of pulse shortening in experiments. Our research indicates that the two main mechanisms leading to the pulse shortening are the electron beam interruption and combining effects of the explosive field electron emission and the secondary electron multipactor on the surface of the slow-wave structure. In order to enhance its power capacity the electrodynamic structure is modified by detailed analysis of the field distribution in the coaxial slow-wave structure. The appropriate resonant reflector and the electron collector are developed for the application of the coaxial relativistic backward wave oscillator. A series of surface treatment is applied to enhance the power capacity of the coaxial RBWO. In the experiment, the microwave pulse duration is increased from less than 10 ns to 20 ns, and the output efficiency is enhanced from less than 20% to 34% employing the electron beam pulse of the full width at half maximum 28 ns. The peak power of 1.01 GW at the frequency of 7.4 GHz is achieved. It is found that the output efficiency of the coaxial RBWO is likely to be advanced if its power capacity can be boosted further.

Microwave generation enhancement of X-band CRBWO by use of coaxial dual annular cathodes

“…The numerical and experimental research results indicate that the diode impedance of CRBWO with a single annular beam is approximately 100 . 7,8 However, by using the coaxial dual annular cathode, the parallel impedance of the diode can be reduced to 40 , while the efficiency remains higher than 30%. The diode impedance of 40 can be matched to the characteristic impedance of the pulse-transmission line of our accelerator.…”

“…The highest experimental efficiency for CRBWO published to date is 36%, corresponding to an output power of 1.01 GW in the X-band. 8 In lower bands, the maximum output power value obtained through numerical simulation is less than 1.7 GW with a conversion efficiency of more than 30%. 13,14 However, in the corresponding experiments, the output power is 1.07 GW and the conversion efficiency is about 18%.…”

“…5 Theoretical analysis 6 and numerical simulations 3 of CRBWO predicted that its conversion efficiency would be higher than 35%, and this has been validated experimentally. 7,8 Although CRBWO is notable for its high conversion efficiency, the output powers obtained experimentally remain around the 1 GW level. This means that the output power of CRBWO is not as attractive as its conversion efficiency, particularly when compared with the output powers of 3-5 GW that have been produced experimentally by conventional hollow RBWOs in recent years.…”

Generation of beating wave by multi-coaxial relativistic backward wave oscillator

“…CRBWO is a new type of HPM source device remarked by its high conversion efficiency (Ge et al, 2010a;Teng et al, 2013a), compact structure (Gao et al, 2011), and frequency tunability (Ge et al, 2010b). CRBWO is a new type of HPM source device remarked by its high conversion efficiency (Ge et al, 2010a;Teng et al, 2013a), compact structure (Gao et al, 2011), and frequency tunability (Ge et al, 2010b).…”

“…Inspired by the distinguishing structure and the physical characteristics of CRBWO, the multi-coaxial relativistic backward wave oscillator (M-CRBWO) that produce beating wave of narrow-band HPM pulse driven by one accelerator is developed as shown in Figure 2. The fluting electron collector prevents the expansion of the plasma generated by the direct bombardment of the electron beam (Teng et al, 2013a). The coaxial reflector consisting of two cavities located on the inner and outer conductors, which can pre-modulate two electron beams respectively, is employed to enhance the conversion efficiency of the wave-beam interaction in the outer CRBWO (Teng et al, 2009).…”