New slow wave structures for travelling wave tubes
File(s)
Author(s)
Hazell, Jonathan
Type
Thesis
Abstract
This thesis covers the design of slow wave structures for travelling wave tubes, with a specific focus on
those that could be used for operation at millimetre or shorter wavelengths. Serpentine and a coupled
cavity photonic crystal structure are covered in detail, together with the interaction between the
electromagnetic waves they support and the electron gun and magnetic beam focusing systems needed
for a travelling wave interaction.
In Chapter 2, the existing small-signal theory of the travelling wave interaction is introduced and applied
to a serpentine travelling wave tube. A set of synthesis equations for the serpentine structure are then
derived from the analysis and verified with simulation. In Chapter 3, possible improvements to the
serpentine structure for high frequency operation, and operation on harmonics other than the
fundamental (for both the phase and the interaction impedance) are considered. From the investigation
it can be concluded that higher harmonics allow a larger beam current than the fundamental. In Chapter
4, slow wave structures based on photonic crystals are proposed for use in travelling wave tubes. A
specific photonic crystal arrangement – the coupled resonator optical waveguide (CROW) - that does
not appear to have been studied previously in this application is then investigated. The conclusion is
that a CROW is suitable for use in a travelling wave tube and is significantly more manufacturable than
existing approaches. In Chapter 5, the design of a full electron beam system for use with both the
original and the improved slow wave structures is presented. The design of an electron gun, cathode
and collimating magnet using an immersed flow insertion are all covered in detail. In Chapter 6,
conclusions are drawn and avenues for possible future work are presented.
those that could be used for operation at millimetre or shorter wavelengths. Serpentine and a coupled
cavity photonic crystal structure are covered in detail, together with the interaction between the
electromagnetic waves they support and the electron gun and magnetic beam focusing systems needed
for a travelling wave interaction.
In Chapter 2, the existing small-signal theory of the travelling wave interaction is introduced and applied
to a serpentine travelling wave tube. A set of synthesis equations for the serpentine structure are then
derived from the analysis and verified with simulation. In Chapter 3, possible improvements to the
serpentine structure for high frequency operation, and operation on harmonics other than the
fundamental (for both the phase and the interaction impedance) are considered. From the investigation
it can be concluded that higher harmonics allow a larger beam current than the fundamental. In Chapter
4, slow wave structures based on photonic crystals are proposed for use in travelling wave tubes. A
specific photonic crystal arrangement – the coupled resonator optical waveguide (CROW) - that does
not appear to have been studied previously in this application is then investigated. The conclusion is
that a CROW is suitable for use in a travelling wave tube and is significantly more manufacturable than
existing approaches. In Chapter 5, the design of a full electron beam system for use with both the
original and the improved slow wave structures is presented. The design of an electron gun, cathode
and collimating magnet using an immersed flow insertion are all covered in detail. In Chapter 6,
conclusions are drawn and avenues for possible future work are presented.
Version
Open Access
Date Issued
2017-12
Date Awarded
2018-05
Copyright Statement
Attribution NoDerivatives 4.0 International Licence (CC BY-ND)
Advisor
Lucyszyn, Stepan
Sponsor
Engineering and Physical Sciences Research Council
Publisher Department
Electrical and Electronic Engineering
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)