High-Power X-Band Relativistic Backward-Wave Oscillator with Exceptional Synchronous Regime Operating at an Exceptional Point

An exceptional point of degeneracy (EPD) is induced in a system made of a linear electron beam interacting with an electromagnetic (EM) guided mode in a vacuum tube made of a corrugated circular metallic waveguide with distributed output ports. This scheme enables an exceptional synchronous regime in backward-wave oscillators (BWOs) where the electron beam provides distributed gain to the EM mode with distributed power extraction. Particle-in-cell (PIC) simulation results demonstrate that the proposed EPD BWO has a starting-oscillation current that scales quadratically with BWO length to a nonvanishing value, which does not occur in standard BWOs and demonstrates the occurrence of the EPD and hence the exceptional synchronism operational regime. The degeneracy of two interactive hot modes is also verified by observing the coalescence of their complex-valued wave numbers at the EPD frequency. Observations on the kinetic energy distribution of the electrons along the BWO demonstrate that the proposed EPD-BWO regime is capable of achieving higher power conversion efficiency at higher levels of power generation due to its ability to maintain the synchronism for longer BWO lengths compared to the standard BWO regime of operation