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{\mathbf { r}}_{\mathbf {o}{\mathbf {1}}}{\mathbf {=4.01 }} cm loaded with a spiral MTM SWS can radiate the TM01 mode with output power {\mathbf {1.06}} GW and frequency 945 MHz using a pulsed electron beam with energy {\mathbf {700 keV}} (U = 700 kV) and current {\mathbf {2 kA}} with a magnetic field \mathbf {B}{\mathbf {=0.58 T}} , 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 TM01 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.