S.B. Dabagov

Peculiarities of photon transmission through capillary systems

Abstract In this paper a theoretical model for calculation of X-ray photons characteristics under passage through capillary systems is described. The model is based on a numerical solution of a wave equation. It is shown that recently discovered interference effect under multiple reflection of X-rays is a display of wave properties of X-rays. In this report an explanation of the observed phenomenon is given.

The UA9 experimental layout

The UA9 experimental equipment was installed in the CERN-SPS in March 09 with the aim of investigating crystal assisted collimation in coasting mode. Its basic layout comprises silicon bent crystals acting as primary collimators mounted inside two vacuum vessels. A movable 60 cm long block of tungsten located downstream at about 90 degrees phase advance intercepts the deflected beam. Scintillators, Gas Electron Multiplier chambers and other beam loss monitors measure nuclear loss rates induced by the interaction of the beam halo in the crystal. Two Roman pots installed in the path of the deflected particles are equipped with a Medipix detector to reconstruct the transverse distribution of the impinging beam. Finally UA9 takes advantage of an LHC-collimator prototype installed close to the first Roman pot to help in setting the beam conditions and to analyze the efficiency to deflect the beam. This paper describes in details the hardware installed to study the crystal collimation during 2010.

Interference phenomenon under focusing of synchrotron radiation by a Kumakhov lens

Abstract Results of experimental and theoretical studies on focusing of synchrotron radiation by means of capillary lenses are presented. For the explanation of the interference effect observed the wave the channeling theory is applied.

On propagation of X-rays in capillary channels

In the last years several coherent phenomena associated with propagation of soft X-ray radiation through capillary optical elements (polycapillary lenses and systems of capillaries) have been observed and investigated. Unexpected effects produced by soft X-radiation traveling inside assembled capillary systems may be explained in the framework of surface wave propagation theory. In this paper theoretical analysis on dependence of the transmission characteristics on capillary wall surface is presented.

Planar channeling radiation by relativistic electrons in different structures of silicon carbide

Spectral distributions of channeling radiation by relativistic electrons channeled in different crystallographic planes of different types of polytype silicon carbide crystals such as hexagonal, zincblende and rhombohedral are presented. For every structure we have found the planes where the emission of channeling radiation is possible. Using the Doyle-Turner approximation to the atomic scattering factor and taking in to account thermal vibrations of crystal atoms, the continuum potentials for different planes in different structures of a SiC single crystal have been calculated. In the framework of quantum mechanics, the theory of channeling radiation was applied to calculate transverse electron states, transition energies, radiation linewidths, the depth dependence of the occupation of quantum states and spectral-angular distributions of channeling radiation. At electron energies larger than 100 MeV, the trajectories, velocities and accelerations of channeled electrons have been obtained by means of classical mechanics, and the spectral-angular distributions were calculated by means of classical electrodynamics using realistic trajectories, velocities and accelerations of channeled electrons. Specific properties of planar channeling radiation generated in different structures of SiC are discussed.

Observation of channeling in bent crystals at the CERN LHC

The feasibility of crystal-assisted collimation is being investigated for improvements of the LHC collimation system, as a part of the future high luminosity upgrade of the CERN LHC (HL-LHC). Two high-accuracy goniometers, each equipped with one bent silicon crystal, were installed in the betatron cleaning insertion of the LHC in 2014. During dedicated tests in 2015, bent crystals were approached to the circulating the beams to test their usage as a first stage in a crystal-based system, both with proton and Pb ion beams. Tests were performed with protons at injection energy (450 GeV/c) and at flat top (6.5 TeV/c), and with ions at injection energy (450 Z GeV/c). A reduction of losses immediately downstream of the crystals was observed in optimum channeling orientation, demonstrating for the first time channeling at these energies. Halo cleaning efficiency of the crystal-based collimation system was also measured.