M. V. Shevelev

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.

Direct Observation of a Semi-Bare Electron Coulomb Field Recover

The problem of semi-bare electron was first considered in frame of quantum electrodynamics by E.L. Feinberg in 1980. In theory in frame of classical electrodynamics this problem was touched on in articles of N.F. Shulga and X. Artru. In 2008 the experimental investigations of this phenomenon in millimeter wavelength region were started by the group of scientists, including authors of this article. Used technique allowed us to study this effect in macroscopic mode. In this paper we present the results of direct observation of a semi-bare electron coulomb field recovery. The semi-bare state was obtained by passing of electron beam through the hole in a conductive screen. Measured spatial distribution of electromagnetic field shows the process of recover of the electron coulomb field, which is followed by a forward radiation. The experiments were performed on the relativistic electron beam of the microtron of Tomsk Polytechnic University.

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.

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.

Coherent forward and backward diffraction radiation of relativistic electrons in a dielectric targets

During the interaction of the relativistic electrons field with a dielectric target various types of electromagnetic radiation, such as Cerenkov radiation, diffraction radiation, transition radiation can be generated. In this report we present the results of experimental studies of the diffraction radiation generated by relativistic electrons in a dielectric target at the interface vacuum-insulator and insulator-conductor in the millimeter wavelength range. The experimental results show that the component of the diffraction radiation of relativistic electrons at the interface insulator-conductor, for any significant refractive index of insulator, is suppressed. The analysis of the results from different points of view was done.

On the role of the surface currents in conducting targets in the formation of the diffraction and transition radiation of relativistic electrons

The surface current method and the pseudophoton method are widely used in the study of the interaction between relativistic electrons and matter. A simple analysis reveals the contradictions between these methods as to the excitation of the currents on the surface of the conducting target. To solve this contradiction, the surface currents on the downstream and upstream surfaces of the conducting target were measured in the geometry of the diffraction radiation. The surface currents were experimentally recorded on the upstream target surface, from which the backward diffraction radiation is generated. At the same time, the surface currents are absent on the downstream target surface, which is conventionally considered as a source of diffraction radiation in the direction of the motion of electrons. Analogous results were obtained in the same geometry in a beam of real photons. On the whole, these results confirm the applicability of the pseudophoton method for the analysis of the effects of the interaction between the field of relativistic photons and the thick (thicker than the skin layer) conducting targets and inapplicability of the surface current method for the radiation in the direction of motion of electrons.