Modeling of RF Pulse Shortening Causes and Their Effects on an Overmoded RBWO Under Low Guiding Magnetic Field

The overmoded slow wave structure (OSWS) and trapezoidal resonant reflector (TRR) have been used to study their effects on the microwave generation time in relativistic backward wave oscillator (RBWO) at the lower guiding magnetic field using a finite difference time domain (FDTD) based particle-in-cell (PIC) simulation “MAGIC” code. Electrons other than the primary electrons and positively charged hydrogen ions (PCHIs) have been identified as the major causes of RF pulse shortening. The pulse shortening analysis has indicated that these causes do not influence the microwave generation time in the overmoded RBWO with TRR for the entire simulation time. The predicted simulation results of the overmoded RBWO with TRR have been justified by comparing with the performances of other RBWO configurations, including a nonovermoded RBWO with rectangular resonant reflector (RR) and TRR individually and an overmoded RBWO with RR provided the inclusion of some of the practical causes of RF pulse shortening. The PIC simulation of pulse shortening analysis predicted that the overmoded RBWO with TRR generated the saturated RF output power of ~0.96 GW at ~3.7 GHz without any pulse shortening with the power duration of at least 70 ns at the lowest guiding magnetic field of ~0.19 T.