Analytic theory of coupled-cavity traveling wave tubes

TL;DR

This paper develops a comprehensive Lagrangian field theory for coupled-cavity traveling wave tubes, incorporating space-charge effects and periodic structure, to better understand their amplification mechanisms and frequency response.

Contribution

It introduces a novel Lagrangian field theory framework for CCTWTs that includes space-charge effects and uses Floquet theory to derive key amplification and dispersion properties.

Findings

Derived closed-form expressions for dispersion relations.

Analyzed frequency-dependent gain characteristics.

Applicable to serpentine traveling wave tubes.

Abstract

Coupled-cavity traveling wave tube (CCTWT) is a high power microwave (HPM) vacuum electronic device used to amplify radio-frequency (RF) signals. CCTWTS have numerous applications, including radar, radio navigation, space communication, television, radio repeaters, and charged particle accelerators. The microwave-generating interactions in CCTWTs take place mostly in coupled resonant cavities positioned periodically along the electron beam axis. Operational features of a CCTWT particularly the amplification mechanism are similar to those of a multicavity klystron (MCK). We advance here a Lagrangian field theory of CCTWTs with the space being represented by one-dimensional continuum. The theory integrates into it the space-charge effects including the so-called debunching (electron-to-electron repulsion). The corresponding Euler-Lagrange equations are ODEs with coefficients varying periodically in the space. Utilizing the system periodicity we develop the instrumental features of the Floquet theory including the monodromy matrix and its Floquet multipliers. We use them to derive closed form expressions for a number of physically significant quantities. Those include in particular the dispersion relations and the frequency dependent gain foundational to the RF signal amplification. Serpentine (folded, corrugated) traveling wave tubes are very similar to CCTWTs and our theory applies to them also.