A New Amplification Regime for Traveling Wave Tubes with Third Order Modal Degeneracy

TL;DR

This paper introduces a novel third order modal degeneracy regime in traveling wave tubes, leveraging stationary inflection points in slow-wave structures to enhance gain, efficiency, and bandwidth in high power microwave amplification.

Contribution

It presents the first investigation of a three-eigenmode synchronization regime at a stationary inflection point in TWTs, offering new design strategies for improved amplifier performance.

Findings

Achieved nearly flat dispersion with zero group velocity at SIP

Demonstrated gain enhancement and efficiency improvements

Showed tunability of SWS parameters for desired dispersion characteristics

Abstract

Engineering of the eigenmode dispersion of slow-wave structures (SWSs) to achieve desired modal characteristics, is an effective approach to enhance the performance of high power traveling wave tube (TWT) amplifiers or oscillators. We investigate here for the first time a new synchronization regime in TWTs based on SWSs operating near a third order degeneracy condition in their dispersion. This special three-eigenmode synchronization is associated with a stationary inflection point (SIP) that is manifested by the coalescence of three Floquet-Bloch eigenmodes in the SWS. We demonstrate the special features of "cold" (without electron beam) periodic SWSs with SIP modeled as coupled transmission lines (CTLs) and investigate resonances of SWSs of finite length. We also show that by tuning parameters of a periodic SWS one can achieve an SIP with nearly ideal flat dispersion relationship with zero group velocity or a slightly slanted one with a very small (positive or negative) group velocity leading to different operating schemes. When the SIP structure is synchronized with the electron beam potential benefits for amplification include (i) gain enhancement, (ii) gain-bandwidth product improvement, and (iii) higher power efficiency, when compared to conventional Pierce-like TWTs. The proposed theory paves the way for a new approach for potential improvements in gain, power efficiency and gain-bandwidth product in high power microwave amplifiers.