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The interaction between a linear electron beam and a guided electromagneticwave is studied in the contest of exceptional points of degeneracy (EPD)supported by such an interactive system. The study focuses on the case of alinear beam traveling wave tube (TWT) with a realistic helix waveguideslow-wave structure (SWS). The interaction is formulated by an analytical modelthat is a generalization of the Pierce model, assuming a one-dimensionalelectron flow along a dispersive single-mode guiding SWS and taking intoaccount space-charge effects in the system. The augmented model using phasevelocity and characteristic impedance obtained via full-wave simulations isvalidated by calculating gain versus frequency and comparing it with that frommore complex electron beam simulators. This comparison also shows the accuracyof our new model compared with respect to the non-dispersive Pierce model. EPDsare then investigated using the augmented model, observing the coalescence ofcomplex-valued wavenumbers and the system's eigenvectors. The point in thecomplex dispersion diagram at which the TWT-system starts/ceases to exhibit aconvection instability, i.e., a mode starts/ceases to grow exponentially alongthe TWT, is the EPD. We also demonstrate the EPD existence by showing that thePuiseux fractional power series expansion well approximates the bifurcation ofthe dispersion diagram at the EPD. This latter concept also explains the"exceptional" sensitivity of the TWT-system to changes in the beam's electronvelocity when operating near an EPD.

Exceptional Degeneracies in Traveling Wave Tubes with Dispersive Slow-Wave Structure Including Space-Charge Effect