Abstract
We show how an exceptional point of degeneracy (EPD) is formed in a system composed of an electron beam interacting with an electromagnetic mode guided in a slow wave structure (SWS) with distributed power extraction from the interaction zone. Based on this kind of EPD, a new regime of operation is devised for backward wave oscillators (BWOs) as a synchronous and degenerate regime between a backward electromagnetic mode and the charge wave modulating the electron beam. Degenerate synchronization under this EPD condition means that two complex modes of the interactive system do not share just the wavenumber, but they rather coalesce in both their wavenumbers and eigenvectors (polarization states). In principle this new condition guarantees full synchronization between the electromagnetic wave and the beam's charge wave for any amount of output power extracted from the beam, setting the threshold of this EPD-BWO to any arbitrary, desired, value. Indeed, we show that the presence of distributed radiation in the SWS results in having high-threshold electron-beam current to start oscillations which implies higher power generation. These findings have the potential to lead to highly efficient BWOs with very high output power and excellent spectral purity.
Highlights
Exceptional points of degeneracy (EPDs) are points in parameter space of a system at which two or more eigenmodes coalesce in their eigenvalues and eigenvectors
We have conceptually demonstrated the occurrence of an exceptional point of degeneracy (EPD) in an interactive system made of a linear electron beam and a guided electromagnetic wave
This EPD condition leads to a new regime of operation for backward wave oscillators (BWOs) where the EPD guarantees a synchronism between a backward wave and a beam’s charge wave through enforcing the coalescence of two modes in both their wavenumber and state vector, a regime we named “degenerate synchronization”
Summary
Exceptional points of degeneracy (EPDs) are points in parameter space of a system at which two or more eigenmodes coalesce in their eigenvalues (wavenumbers) and eigenvectors (polarization states). We investigate an EPD that requires both distributed power extraction and gain being simultaneously present in a waveguide called here as “slow wave structure” (SWS) since its mode is used to interact with an electron beam.
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