An Efficient Coaxial Superradiant Cherenkov Oscillator with Front-extraction Structure Operating at Low Magnetic Field

In the last few decades, significant results have been obtained in the generation of ultrashort powerful microwave pulses using the effect of super-radiance (SR). The super-radiant relativistic backward wave oscillator (SR-RBWO) is the most representative SR microwave device. In this paper, an improved X-band front-extraction SR-RBWO with a more efficient coaxial extraction structure is proposed. The improved coaxial front-extraction structure with higher extraction efficiency is designed to further increase the conversion efficiency of the device. The SR pulse is almost completely extracted by the coaxial extractor and coupled into the coaxial waveguide with TEM mode to output. With the improved more efficient coaxial extractor, the conversion factor can be increased significantly. Particle-in-cell simulation demonstrates that as the rising front of the diode voltage pulse is 1.55 ns and the maximum value is 200 kV, the beam current is 3.44 kA, and the magnetic field of 0.32 T, a powerful SR pulse with peak power of 2.5 GW and ultra-short pulse width of 0.25 ns can be generated. The corresponding power conversion factor K=3.6, which is the maximum that can be obtained in SR-RBWOs research with a low guiding magnetic field currently.