Abstract
We propose an oversized coaxial Cherenkov generator to generate ultrashort pulses with extremely high peak power exceeding 100 GW. The oversize factor of the device is about 5, which ensures sufficient power handling capacity for ultrashort pulses and a very high beam current, and thus the driving power. An optimized profiled slow wave structure (SWS) with squarely increasing corrugation amplitude, rather than linearly increasing function, and a uniform SWS with a slightly larger corrugation period are used to provide better beam-wave interaction and accomplish energy accumulation of electromagnetic wave from the gradually developed bunches precisely and continuously. The operation mode in the coaxial SWS is quasi-TEM mode, which is almost completely reflected by the coaxial reflector and coupled into the coaxial coupler with the mixed TEM mode and coaxial TM01 mode. This kind of single-pass output eliminates the power loss caused by conventional case as the pulse re-enters the SWS. Particle-in-cell simulations show that as the diode voltage is 760 kV and beam current is 78 kA, an ultrashort pulse of 0.4 ns with peak power of 129 GW and frequency range from 9.06-10.66 GHz is generated. The corresponding conversion factor is up to 2.18.