Parametric X-ray radiation in the Smith-Purcell geometry for non-destructive beam diagnostics

TL;DR

This paper explores parametric X-ray radiation generated by ultra-relativistic electron beams near crystal surfaces in a Smith-Purcell-like geometry, enabling non-destructive beam diagnostics without disturbing the beam.

Contribution

It introduces a novel geometry for PXR generation that allows non-invasive beam diagnostics by utilizing X-ray emission along the crystal normal without multiple scattering effects.

Findings

X-ray radiation occurs along the crystal normal in this geometry.

The majority of electrons do not undergo multiple scattering.

This method can be used for non-destructive beam diagnostics.

Abstract

We investigate parametric X-ray radiation (PXR) under condition of the extremely asymmetric diffraction, when the ultra-relativistic electron bunch is moving in \textit{vacuum} parallel to the crystal-vacuum interface, close to the crystal surface. This type of geometry coincides with the well known mechanism of generation of radiation, when the self-field of the particle beam interacts with the reflecting metal grating, namely the Smith-Purcell effect. We demonstrate that in this geometry the main contribution is given via a tail region of the beam distribution, which penetrates the crystal and X-rays are radiated along the normal to the crystal surface. We determine the electron beam characteristics, when this phenomenon can be observed. It is essential that in this geometry the majority of electrons does not undergo multiple scattering and consequently the characteristics of the particle beam are not changed, thus allowing the usage of the emitted X-rays for the purpose of non-destructive beam diagnostics, which can complement the traditional knife-edge method.