"Shadowing" of the electromagnetic field of relativistic charged particles

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 γ 2 λ. 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.

Classical and quantum phenomenology in radiation by relativistic electrons in matter or in external fields

“…A screen whose contour is close to the electron trajectory intercepts part of the equivalent photon cloud, making a shadow in the formation zone [18,19]. This has been verified in an experiment at Tomsk [20] schematized in Fig.1, left. Shadowing limits in an essential way the SmithPurcell radiation, since each ridge of the grating makes a shadow on the next one.…”

“…Then (20) and (21) agree. However they give different results when ω ∼ ǫ or ν ∼ n. Note that ν ≪ n usually implies ω ≪ ǫ, therefore we can conclude that the BK spectral lines are shifted only for the high harmonics.…”

Direct Observation of a Semi-Bare Electron Coulomb Field Recover

“…The problem of field radiation of electrons emitted from the absorber in the form of "blackbody", was considered in [9], but the solution is done for the far zone (at infinity) and does not consider the dynamics of the field within the zone of radiation formation, which is more interesting for us. In [10] we studied the dynamics of electrons in condition of a field of shadow effect from conducting and absorbing screen. The studies were based on the radiation characteristics of semi-bare electrons downstream to conductive target, or based on the evolution of the electron field pseudo-photons, diffracted on an electron dump, in which the electrons are stopped.…”

Radiation Induced by Charged Particles in Optical Fibers

“…Beyond this region, called formation zone, the cloud of virtual photons of wavelength λ is practically restored if there is no other piece of matter in the formation zone. The shadow effect has been directly observed in diffraction radiation (19). In the case of mettalic balls it is included in the rescattering effects studied by García et al (20).…”