Concepts of Time-frequency Structure and Pulse Compression of X-band Radiation Generated by an Oversized Coaxial Cherenkov Generator

New concepts to generate extremely high output power with ultrashort pulse duration are developed. At first, an oversized coaxial Cherenkov generator with a profiled and extended slow wave structure is used to generate a time-frequency-modulated pulse with power of several tens of GW and duration of several nanoseconds. Then this time-frequency-modulated pulse can be compressed into a sub-nanosecond pulse with power exceeding 100 GW via a circular waveguide compressor after mode conversion. As an example, particle-in-cell simulation demonstrates that a pulse is obtained with power of 35 GW, duration of 3.0 ns, and frequency sweeping from 8.9 GHz to 11.0 GHz almost linearly. Injecting this pulse into a circular waveguide as TE 01 mode, it can be compressed into an ultrashort pulse with power of 168 GW and duration of 0.45 ns. Compared with previous method of producing superradiance pulse directly, the beam-wave interaction in the generator is not so highly unstable, and thus the whole system is more reliable and controllable.