Influence of distance between bragg reflector and slow wave structure on output power of relativistic barkward wave oscillator

This paper theoretically analyzes the influence of distance between Bragg reflector and slow wave structure on output power of relativistic backward wave oscillator (BWO). According to the phase relation between the RF current in electron beam and axial electric field in structure, the optimal distances are suggested. More analyses on this characteristic of BWO with Bragg reflector has been conducted with numerical simulation, which indicates that microwave output power of BWO is high near the optimal distances predicted by theoretical analysis. Finally, in experiments of the BWO with Bragg reflector driven by SINUS-881 accelerator, when magnetic field was 2.7 T, diode voltage 650 kV, and beam current 9.1 kA, a microwave output of 2 GW, 9.35 GHz was generated, and conversion efficiency was up to 33.8%. Experimental results showed that there were several output power peaks varied with the distance between Bragg reflector and slow wave structure and the output power of microwave was the highest near the second optimal distance regime than the others, which agreed with the theoretical and numerical analysis.