"Shadowing" of the electromagnetic field of relativistic charged particles

TL;DR

This paper investigates the shadowing effect of the electromagnetic field of relativistic electrons passing near screens, showing how it influences diffraction radiation and sets limits on Smith-Purcell radiation intensity.

Contribution

It provides experimental evidence of the shadowing effect on coherent diffraction radiation and compares effects of absorbing and conductive screens, highlighting their similar influence.

Findings

Shadowing reduces radiation intensity at small distances from the screen.

Absorbing and conductive screens produce similar shadowing effects.

Shadowing limits the intensity of Smith-Purcell radiation.

Abstract

In radiation processes such as a transition radiation, diffraction radiation, etc. based on relativistic electrons passing through or near an opaque screen, the electron self-field is partly shadowed after the screen over a distance of the order of the formation length $\gamma^2\lambda$. This effect has been investigated on coherent diffraction radiation (DR) by electron bunches. Absorbing and conductive half-plane screens were placed at various distances L before a standard DR source (inclined half-plane mirror). The radiation intensity was reduced when the screen was at small L and on the same side as the mirror. No reduction was observed when the screen was on the opposite side. It is worth noting that absorbing and conductive half-plane screens produce the same shadowing effect. The shadowing effect is responsible for a bound on the intensity of Smith-Purcell radiation.