A. P. Potylitsyn

Transition radiation and diffraction radiation. Similarities and differences

Abstract The characteristics of diffraction radiation (DR), i.e. radiation of the charged particle moving near conducting target have been considered for an ultrarelativistic case. The simple expressions for DR fields for the semi-infinite ideal conducting target have been derived. The close connection between transition radiation (TR) and DR has been shown. The effect of finite transversal sizes of target on TR characteristics has been evaluated.

Measurement of spectral and polarization characteristics of parametric X-rays in a Si crystal

Abstract Spectral distributions of parametric X-rays (PX) have been measured for 900 MeV electrons transmitted through a Si crystal. A displacement of the PX spectral line was observed with the crystal rotation and in scanning PX radiation reflection by a detector. A high degree of linear polarization (P = 0.8) of parametric X-rays was obtained.

Experimental search of parametric X-ray radiation in a silicon crystal at a small angle near the velocity direction of relativistic electrons

Abstract At the Tomsk synchrotron measurements of X-ray yield for the energies ω=29–53 keV emitted in the forward direction from a perfect silicon crystal bombarded by 500-MeV relativistic electrons have been carried out. The contribution of parametric X-ray radiation (PXR) at a small angle near the velocity direction of electrons has not been observed. The possible maximum value of this radiation is smaller than 2% of the total intensity of bremsstrahlung and transition radiation.

Measurement of the angular characteristics of transition radiation in near and far zones

A method is developed for measuring the angular distribution of radiation in the near zone that excludes the contribution of the sizes of a radiation source to angular characteristics. Using this method, absolute measurements of the angular distribution of coherent transition radiation are performed in the millimeter wavelength range. It is shown that the measured characteristics correspond to the respective theoretical characteristics obtained in the far zone approximation.

Feasibility of optical diffraction radiation for a non-invasive low-emittance beam diagnostics

Abstract A “proof-of-principle” experiment on the optical diffraction radiation (ODR) as a single-pulse beam profile monitor is planned using an electron beam extracted from the KEK-ATF damping ring. The main goals of this experiment are the following: (i) To measure the yield and the angular distributions of the optical diffraction radiation from a large-size target at different wavelengths, impact parameters and beam characteristics for a comparison with analogous characteristics of optical transition radiation from a foil with identical optical parameters and for a verification of the model assumption (perfectly conducting semi-infinite target). (ii) To investigate the ODR angular distributions from a tilted target with a slit for observing the interference effects. (iii) To compare the results obtained by simulations based on classical approaches, taking into account the optical characteristics of the equipment and the beam parameters. (iv) To estimate the prospects of using ODR as a new non-invasive tool for ultrarelativistic beams. We estimated that the ODR photon yield in 10% bandwidth for 500 nm is about 106 photons/bunch with an impact parameter of 100 μm . This indicates that the ODR monitor is a promising candidate for single-pulse beam-profile measurements, and that it will be an extremely useful instrument for future linear colliders (JLC, NLC, TESLA and CLIC).

Focusing of transition radiation and diffraction radiation from concave targets

In the article the transition radiation from a relativistic charge crossing a finite radius paraboloid target with taking into account the pre-wave zone effect is considered. It is shown that in this case the radiation cone narrowing occurs in contrast with the transition radiation from the flat target if the detector is situated at the distance, which is smaller than the focus distance (the focusing effect) from the target. At the charged particle passage through the central hole in a paraboloid target the diffraction radiation focusing (DR) occurs too. The focusing of coherent DR for the non-invasive measuring of the electron bunch length is proposed.

Diffraction of real and virtual photons in a pyrolytic graphite crystal as source of intensive quasimonochromatic X-ray beam

Abstract A series of experiments on the parametric X-rays radiation (PXR) generation and radiation soft component diffraction of relativistic electrons in pyrolytic graphite (PG) crystals have been carried out at the Tomsk synchrotron. It is shown that the experimental results with PG crystals are explained by the kinematic PXR theory if we take into account a contribution of the real photons diffraction (transition radiation, bremsstrahlung and PXR photons as well). The measurements of the emission spectrum of channeled electrons in the photon energy range much smaller than the characteristic energy of channeling radiation have been performed with a crystal-diffraction spectrometer. For electrons incident along the 〈1 1 0〉 axis of a silicon crystal, the radiation intensity in the energy range 30⩽ω⩽360 keV exceeds the bremsstrahlung one almost by an order of magnitude. Different possibilities to create an effective source of the monochromatic X-ray beam based on the real and virtual photons diffraction in the PG crystals have been considered.

Experimental observation of parametric X-ray radiation directed along the propagation velocity of relativistic electrons in a tungsten crystal

Parametric X-ray radiation (PXR) due to dynamic diffraction of relativistic electrons is experimentally observed at small angles to the propagation velocity of electrons in a tungsten crystal. The specific features of the experimental method are described, and forward PXR reflections from two crystallographic planes of tungsten are reliably measured.

Resonant diffraction radiation from an ultrarelativistic particle moving close to a tilted grating.

A simple model for calculating the diffraction radiation characteristics from an ultrarelativistic charged particle moving close to a tilted ideally conducting strip is developed. Resonant diffraction radiation (RDR) is treated as a superposition of the radiation fields for periodically spaced strips. The RDR characteristics have been calculated as a function of the number of grating elements, tilted angle, and initial particle energy. An analogy with both the resonant transition radiation in an absorbing medium and the parametric x-ray radiation is noted.

SMITH-PURCELL EFFECT AS RESONANT DIFFRACTION RADIATION

Abstract The radiation of ultrarelativistic charged particle passing near a grating (Smith–Purcell radiation (SPR)) has been considered on the basis of a simple physical model, where SPR is treated as the resonant diffraction radiation (RDR). The apparent analogy between RDR and a well known resonant transition radiation has been used. The results have been compared with those obtained via other approaches. For an ultrarelativistic case it has been shown that the SPR intensity for a grating designed from strips separated by vacuum gaps sufficiently exceeds the one for traditional grating made up by a periodically deformed continuous surface.