  Abstract An exceptional point of degeneracy (EPD) is induced in a system made
of an electron beam interacting with an electromagnetic (EM) guided mode. This
enables a degenerate synchronous regime in backward wave oscillators (BWOs)
where the electron beams provides distributed gain to the EM mode with
distributed power extraction. Current particle-in-cell simulation results
demonstrate that BWOs operating at an EPD have a starting-oscillation current
that scales quadratically to a non-vanishing value for long interaction lengths
and therefore have higher power conversion efficiency at arbitrarily higher
level of power generation compared to standard BWOs.
