Quasi-Periodic Sequences Generation of Ultrashort Pulses Based on the Superradiance of a Coaxial Cherenkov Generator Operating at Low Magnetic Field

Abstract

A coaxial Cherenkov generator operating at a low magnetic field is proposed to generate ultrashort-pulse quasi-periodic sequences based on the effect of superradiance (SR). The device employs an extended slow wave structure (SWS) with combined variations in corrugation depth and period, resulting in enhanced spectral continuity and higher SR power. Most of the microwave power is coupled into the hollow waveguide formed by the inner conductor of the coaxial SWS. A portion of the SR pulse generated in the coaxial SWS is reflected back into the SWS, where it is primarily absorbed by disturbed electrons rather than seeding the next SR pulse. Particle-in-cell (PIC) simulations demonstrate that under a diode voltage of 720 kV, beam current of 19.2 kA, and guiding magnetic field of 0.54 T, six short pulses with instantaneous peak power of 15.5–28.5 GW and full width half maximum (FWHM) durations of 0.7–1.4 ns are produced within a 50 ns window. The inter-pulse intervals range from 4.4 to 8.8 ns. The frequency is in the X-band with an 800 MHz bandwidth at the −10 dB level. The variations in peak power and timing are thoroughly analyzed, and the physical mechanisms underlying the quasi-periodic ultrashort-pulse formation are elucidated. A new insight is provided that the critical factor for the sequence formation based on the SR effect lies in the recovery of the electron beam to an undisturbed state after each pulse.