Yu Popov

Investigation of coherent Čerenkov radiation generated by 6.1 MeV electron beam passing near the dielectric target

Coherent Cerenkov radiation generated by the 6.1 MeV bunched electron beam travelling near dielectric target (teflon) have been investigated theoretically and experimentally. It has been shown that the longitudinal bunch form-factor plays important role in the characteristics of coherent Cerenkov radiation. We have also compared the characteristics of coherent Cerenkov radiation and the ones of coherent diffraction radiation from a metal target in the similar conditions and have shown that coherent Cerenkov radiation is more intensive. These facts make coherent Cerenkov radiation a promising mechanism for a new noninvasive beam diagnostic technique.

Shadowing of the electromagnetic field of relativistic charged particles

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 γ2λ. 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.

SHADOWING OF THE ELECTROMAGNETIC FIELD OF A RELATIVISTIC ELECTRON

In coherent radiation sources (diffraction radiation, Smith-Purcell effect, etc.) based on relativistic electrons passing by a material radiator, the electron self-field is partly shadowed after each part of the radiator over a distance of the order of the formation length g2l. This effect has been investigated on coherent diffraction radiation (DR) by electron bunches. An absorbing half-plane screen was placed at various distances L before a standard DR source (inclined half-plane mirror). The DR 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. The shadowing effect can significantly reduce the total energy radiated in a long radiator.

Detection of diffraction radiation in a dielectric target simultaneously with Cherenkov radiation

The effect of the simultaneous generation of Cherenkov radiation and diffraction radiation in a dielectric target by electrons that pass near it has been experimentally studied. It has been shown that diffraction radiation appears at the upstream edge of the dielectric target, propagates inside the target, and is refracted at the down-stream edge as a beam of real photons.

Macroscopic effect of the shadow of the electromagnetic field of relativistic electrons

The effect of the “formation zone” (“shadow” effect) on the characteristics of coherent diffraction radiation from a relativistic electron bunch passing near two conducting targets has been investigated experimentally as a function of the distance between the targets. The effect of the shadow behind absorbing and conducting screens on the diffraction radiation intensity has been studied in the experiments. In both cases, the same decrease in the diffraction radiation intensity almost to zero is observed with a decrease in the distance between the shadow source and target. The results indicate that two interpretations of the observed effect—the formation zone and shadow effect—are not equivalent.

Experimental Research of the Diffraction and Vavilov-Cherenkov Radiation Generation in a Teflon Target

Geometry of Vavilov-Cherenkov (VChR) radiation when an electron moves close to a dielectric target is in analogy to diffraction radiation (DR) geometry. In this case we may expect DR generation from the upstream face of the target besides that VChR. The joint observation of these booth types of radiation is very interesting from the pseudo-photon viewpoint, which is applicable for relativistic electrons. Unexpected results obtained in our experiment insist on reflection about nature both DR and VChR. The experiment was performed on the relativistic electron beam of the microtron of Tomsk Polytechnic University.

Investigation of Coherent Vavilov-Cherenkov Radiation in the Millimeter Wavelength Range Generated in PTFE and Paraffin Target

In this paper, we present an experimental observation of coherent Cherenkov radiation in the millimeter wavelength range. Coherent Cherenkov radiation is generated by a 6.1-MeV bunched electron beam passing by dielectric targets (PTFE and paraffin). The characteristics of Cherenkov and diffraction radiation measured under the same conditions are compared. The experiment is carried out with the electron beam of the microtron at Tomsk Polytechnic University.

THE EXPERIMENTAL STUDY OF THE SURFACE CURRENT EXCITATION BY A RELATIVISTIC ELECTRON ELECTROMAGNETIC FIELD

The problem of the surface current excitation in a conductive targets by a relativistic electron electric field as the origin of such radiation mechanisms as diffraction and transition radiation of relativistic electron was considered in frame of both surface current and pseudo-photon methods. The contradiction between these viewpoints in respect to the surface current on the target downstream surface necessitated the experimental test of this phenomenon. The test performed on electron beam of the 6 MeV microtron showed, that not any surface current is induced on the target downstream surface under the influence of a relativistic electron electromagnetic field in contrast to the upstream surface. This is important implication for the understanding of the forward transition and diffraction radiation nature.

Characteristics of Smith-Purcell radiation in millimeter wavelength region

Investigations of the Smith-Purcell radiation (SPR) were began with non-relativistic electron beams with some unexpected experimental results. Further the experimental investigations were performed with relativistic electron beams for application to beam diagnostics. Large discrepancy between different theoretical models significantly increases the role of experimental studies of this phenomenon. In this report we present some problems and features of experimental investigations of SPR in millimeter wavelength region. The problems of prewave zone and coherent effects are considered. The shadowing effect, focusing of radiation using a parabolic SPR target and effect of inclination of target strips were investigated with moderately relativistic electron beam.

Experimental investigations of backward transition radiation characteristics in extreme ultraviolet region

This report summarizes the results of an experiment dedicated to the observation of backward transition radiation in the EUV spectral region. This radiation was generated by an 855MeV electron beam at a molybdenum target. The radiation characteristics in the EUV region are compared to those in the optical region. It was shown that the radiation measured in the EUV region was more intense than theoretically predicted. As a result the EUV radiation yield seems to be sufficient for standard beam profile diagnostics.