Electromagnetic field features at interaction of relativistic electron with matter

The features of electromagnetic field of relativistic electrons passing through a hole in an absorbing screen as a function of the distance from the screen in the range of radiation formation length were investigated for the transversal and longitudinal field components. The analysis of the obtained results allows approving the existence of a semi-bare electron with a particularly deprived Coulomb field, which turns into the stable state of the usual electron at the distance of radiation formation length

“Shadowing” of the electromagnetic field of relativistic charged particles

VIII International Symposium Radiation from Relativistic Electrons in Periodic Structures (RREPS-09), Zvenigorod, Russia, Sept. 7-11, 2009International audienceIn 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

Experimental test of the shadowing effect in Smith-Purcell radiation

The observation of a shadowing effect of a relativistic electron Coulomb field for the Smith-Purcell radiation generation is presented in this paper. For this purpose the surface current from the closest surface of grating element to the electron beam was measured for a downstream one shadowed by upstream element. The experimental results showed that shadowing effect for Smith-Purcell radiation depends on grating geometry

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

Geometry of Vavilov-Cherekov (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.Comment: This article will be published in Journal of Physic

The coherent Vavilov-Cherenkov radiation for a bunch length diagnostic

Coherent Vavilov-Cherenkov radiation generated by a 6.1MeV bunched electron beam traveling in the vicinity of a solid dielectric target (PTFE and Paraffin) has been investigated experimentally. In addition, we have also demonstrated the simple scheme of the Cerenkov interferometer for non-invasive longitudinal electron bunch length diagnostics

Evolution of the Velocity Ellipsoids in the Thin Disk of the Galaxy and the Radial Migration of Stars

Data from the revised Geneva--Copenhagen catalog are used to study the influence of radial migration of stars on the age dependences of parameters of the velocity ellipsoids for nearby stars in the thin disk of the Galaxy, assuming that the mean radii of the stellar orbits remain constant. It is demonstrated that precisely the radial migration of stars, together with the negative metallicity gradient in the thin disk,are responsible for the observed negative correlation between the metallicities and angular momenta of nearby stars, while the angular momenta of stars that were born at the same Galactocentric distances do not depend on either age or metallicity. (abridged)Comment: Astronomy Reports, Vol. 86 No. 9, P.1117-1126 (2009

Formation of Galactic Systems in Light of the Magnesium Abundance in Field Stars: The Thin Disk

We analyze the relations between the relative magnesium abundances in stars and their metallicities, Galactic orbital elements, and ages. The relative magnesium abundances in metal-poor ([Fe/H] < -0.4) thin-disk stars have been found to systematically decrease with increasing stellar orbital radii in such a way that magnesium over abundances ([Mg/Fe]>0.2 dex) are essentially observed only in the stars whose orbits lie almost entirely within the solar circle. At the same time, the range of metallicities in magnesium-poor stars is displaced from (-0.5<[Fe/H]<+0.3 dex) to (-0.7<[Fe/H]<+0.2 dex) as their orbital radii increase. This behavior suggests that, first, the star formation rate decreases with increasing Galactocentric distance and, second, there was no star formation for some time outside the solar circle while this process was continuous within the solar circle. The decrease in the star formation rate with increasing Galactocentric distance is responsible for the existence of a negative radial metallicity gradient (grad_{R}[Fe/H]=(-0.05 \pm 0.01) kpc^{-1}) in the disk, which shows a tendency to increase with decreasing age. At the same time the relative magnesium abundance exhibits no radial gradient. We have confirmed the existence of a steep negative vertical metallicity gradient (grad_Z [Fe/H]=(-0.29 \pm 0.06) kpc^{-1}) and detected a significant positive vertical gradient in relative magnesium abundance (grad_Z [Mg/Fe]=(0.13 \pm 0.02) kpc^{-1}); both gradients increase appreciably in absolute value with decreasing age. We have found that there is not only an age-metallicity relation, but also an age-magnesium abundance relation in the thin disk.Comment: accepted 2006, Astronomy Letters, Vol. 32 No. 6, P.376-392, 14 pages, 10 figure

Site- and spin-dependent coupling at the highly ordered h-BN/Co(0001) interface

Using photoelectron diffraction and spectroscopy, we explore the structural and electronic properties of the hexagonal boron nitride (h-BN) monolayer epitaxially grown on the Co(0001) surface. Perfect matching of the lattice parameters allows formation of a well-defined interface where the B atoms occupy the hollow sites while the N atoms are located above the Co atoms. The corrugation of the h-BN monolayer and its distance from the substrate were determined by means of R-factor analysis. The obtained results are in perfect agreement with the density functional theory (DFT) predictions. The electronic structure of the interface is characterized by a significant mixing of the h-BN and Co states. Such hybridized states appear in the h-BN band gap. This allows to obtain atomically resolved scanning tunneling microscopy (STM) images from the formally insulating 2D material being in contact with ferromagnetic metal. The STM images reveal mainly the nitrogen sublattice due to a dominating contribution of nitrogen orbitals to the electronic states at the Fermi level. We believe that the high quality, well-defined structure and interesting electronic properties make the h-BN/Co(0001) interface suitable for spintronic applications.L.V.Ya. acknowledges the RSF (Grant No. 16-42-01093). A.V.T., V.O.S., K.A.B., O.Yu.V., and D.Yu.U. acknowledge St. Petersburg State University for research Grant No. 11.65.42.2017. M.V.K. and I.I.O. acknowledge the RFBR (Grant No. 16-29-06410). C.L. acknowledges the DFG (Grant Nos. LA655-17/1 and LA655-19/1).Peer reviewe