Wake fields in a rectangular dielectric-lined accelerating structure with transversal isotropic loading

TL;DR

This paper derives analytical solutions for wakefields in rectangular dielectric waveguides with transversal isotropic loading, showing how dielectric anisotropy influences the excitation parameters and frequency characteristics of the generated Cherenkov and Coulomb fields.

Contribution

It provides the first analytical expressions for wakefields in rectangular waveguides with transversal isotropic dielectric loading, including effects of anisotropy on wakefield properties.

Findings

Dielectric anisotropy causes a frequency shift in wakefields.

Analytical superpositions of LSM and LSE modes are derived.

Numerical modeling confirms the impact of anisotropy on wakefield characteristics.

Abstract

Dielectric lined waveguides are under extensive study as accelerating structures that can be excited by electron beams. Rectangular dielectric structures are used both in proof of principle experiments for new accelerating schemes and for studying the electronic properties of the structure loading material. Analysis of Cherenkov radiation generated by high current relativistic electron bunch passing through a rectangular waveguide with transversal isotropic dielectric loading has been carried out. Some of the materials used for the waveguide loading of accelerating structures (sapphire, ceramic films) possess significant anisotropic properties. In turn, it can influence excitation parameters of the wakefields generated by an electron beam. General solutions for the fields generated by a relativistic electron beam propagating in a rectangular dielectric waveguide have been derived using the orthogonal eigenmode decomposition method for the transverse operators of the Helmholtz equation. The analytical expression for the combined Cherenkov and Coulomb fields in terms of a superposition of LSM and LSE-modes of rectangular waveguide with transversal isotropic dielectric loading has been obtained. Numerical modelling of the longitudinal and transverse (deflecting) wakefields has been carried out as well. It is shown that the dielectric anisotropy causes frequency shift in comparison to the dielectric-lined waveguide with the isotropic dielectric loading.