Vector electromagnetic theory of transition and diffraction radiation with application to the measurement of longitudinal bunch size

TL;DR

This paper introduces a vector electromagnetic theory-based method for accurately calculating transition and diffraction radiation, enabling improved diagnostics of particle bunch sizes through angular distribution analysis.

Contribution

It presents a novel vector electromagnetic approach that generalizes scalar models, allowing precise predictions of TR and DR in near and far fields for the first time.

Findings

Vector theory predicts polarization and spectral distributions accurately.

Scalar models are shown as limiting cases of the vector theory.

Proposes a new technique for measuring bunch length using angular distribution.

Abstract

We have developed a novel method based on vector electromagnetic theory and Schellkunoff's principles to calculate the spectral and angular distributions of transtion radiation (TR) and diffraction radiation (DR) produced by a charged particle interacting with an arbitrary target. The vector method predicts the polarization and spectral angular distributions of the radiation at an arbitrary distance form the source, i.e. in both the near and far fields, and in any direction of observation. The radiation fields of TR and DR calculated with the commonly used scalar Huygens model are shown to be limiting forms of those predicted by the vector theory and the regime of validity of the scalar theory is explicitly shown. Calculations of TR and DR done using the vector model are compared to results available in the literature for various limiting cases and for cases of more general interest. Our theory has important applications in the design of TR and DR diagnostics particularly those that utilize coherent TR or DR to infer the longitudinal bunch size and shape. A new technique to determine the bunch length using the angular distribution of coherent TR or DR is proposed.