PIC Simulations of a Novel Sub-1-GHz Compact Relativistic Cherenkov Oscillator Using Spiral Metamaterials With High Output Power

We developed a novel spiral metamaterial (MTM) unit cell and constructed a slow wave structure (SWS) based on it at sub-1-GHz frequency and developed a compact relativistic Cherenkov oscillator with high efficiency under relatively low guide magnetic field. Particle-in-cell (PIC) simulations demonstrate that a circular waveguide with radius <tex-math notation="LaTeX">r_o1=4.01</tex-math> cm loaded with a spiral MTM SWS can radiate the TM <tex-math notation="LaTeX">₀₁</tex-math> mode with output power <tex-math notation="LaTeX">1.06</tex-math> GW and frequency 945 MHz using a pulsed electron beam with energy <tex-math notation="LaTeX">700 keV</tex-math> ( <tex-math notation="LaTeX">U</tex-math> <tex-math notation="LaTeX">$=$</tex-math> 700 kV) and current <tex-math notation="LaTeX">2 kA</tex-math> with a magnetic field <tex-math notation="LaTeX">B=0.58~T,</tex-math> and the corresponding beam-to-microwave power conversion efficiency is 75.6%. When the applied voltage is varied from 400 to 700 kV, the output frequency of the TM <tex-math notation="LaTeX">₀₁</tex-math> mode is centered at 940 MHz with a beam-tuning frequency bandwidth of 10 MHz, while the output power can be greater than 600 MW. This work seeks to design a compact backward wave oscillator (BWO) for high power for sub-1-GHz generation across a wide voltage range and with low dispersion.