N. Yu. Svechnikov

Special-purpose radiation sources based on the Siberia-2 storage ring

Synchrotron radiation (SR) generated by homogeneous magnetic fields of bending magnets is now employed at the Siberia-2 electron storage ring. It is planned that, in the near future, most of the storage ring’s free straight sections will be equipped with insertion devices (undulators and wigglers). Two projects of specialized radiation sources based on the Siberia-2 stor age ring are discussed. The first source is a vacuum milliundulator intended for generation of extremely bright X-ray beams. An X-ray source with vertically limited diffraction is shown to be feasible when the vertical emittance of an electron beam is equal to the diffraction emittance of photons with an energy of 2 keV. The second source uses edge radiation (ER) generated at the ends of bending magnets of the storage ring. Calculations show that, in the infrared and ultraviolet spectral regions, the ER intensity must exceed the intensity of standard SR formed by the homogeneous field of a bending magnet.

Temperature and spectroscopic characteristics of homogeneous co-deposited carbon–deuterium films produced in the T-10 tokamak

Homogeneous carbon–deuterium (C‒ D) films with a high [D]/[C] ratio, redeposited on deuterium-plasma discharge in the T-10 tokamak, have been studied by means of thermogravimetric analysis, spectroscopy based on electron paramagnetic resonance, Fourier-transform infrared spectroscopy and photoluminescence spectroscopy. Deuterium was found to be accumulated only in the C‒ D2, 3 sp3 vibrational modes, including 633 and 1090 cm−1 deformation modes, and 2100–2200 cm−1 stretching modes, the intensity of which slightly diminished on annealing at 450 °C. Photoluminescence of an excitonic nature was found at 390–530 nm related to the C 2p π−π* transitions within the aromatic rings, and luminescence quenched at 450 °C. The luminescence excitation spectra at 3–10 eV showed similarity in peak positions to the luminescence excitation spectra of thin C60 films. Possible physical reasons explaining the effect of H‒ D‒ T isotopes on the accumulation and desorption of hydrogen are considered.

Reflection spectra of lithium hydride crystals in 4–25 eV range at 5 K

Abstract Reflection spectra of LiH crystals have been studied in the range 4–25 eV, using synchrotron radiation from the storage ring Siberia-1 devised in the Institute of Atomic Energy, Moscow. Resolution of 1.5 meV was achieved with the help of a one-meter vacuum monochromator. The nature of the observed bands is discussed.

Adsorption States of Protium and Deuterium in Redeposited Polymer Hydrocarbon Films from a T-10 Tokamak

Free redeposited hydrocarbon films (flakes) with a high content of deuterium and hydrogen formed in the T-10 tokamak operating at the Russian Research Centre (RRC) “Kurchatov Institute” are studied using thermal desorption spectroscopy (TDS), infrared (IR) spectroscopy, and X-ray diffraction (XRD) analysis. According to the XRD data, the films contain scattering elements with dimensions of about 1 nm and weakly ordered structures. The TDS curves for D2 (H2) consisting of two groups of peaks at 450–800 and 900–1000 K turn out to be sufficiently similar to the spectra of nanographite obtained by milling graphite mechanically. Two main adsorption states with activation energies of ≈0.65 and ≈1.25 eV/N corresponding to hopping diffusion and resonance mechanisms, respectively, were discovered. The difference between the IR spectra of reddish-gold and dark-brown films is due to both a weaker degree of C-H hybridization of dark films and their disordered carbon network whose ends are connected to CD2,3 fragments.

Study of microimpurities and charge states in homogeneous hydrocarbon films (Redeposited from a T-10 tokamak deuterium plasma discharge) using XRF analysis, IR spectroscopy, EPR, and I-V characteristics

Microimpurities and charge states of homogeneous deuterated hydrocarbon films redeposited from a T-10 tokamak deuterium plasma discharge are studied spectroscopically using x-ray fluorescence (XRF) analysis, electron paramagnetic resonance (EPR), infrared (IR) spectroscopy; current-voltage (I-V) charachteristics are also measured. Twelve microimpurities (mainly, those of transition metals Fe, Mo, Cr, Ni, Ti, etc., with relative concentrations of 50–7000 ppm) have been discovered. The resulting broad EPR (9.9 GHz, 6000 G) line with g-factors of g = 2.053–2.093 and g = 4.3 assigned to paramagnetic impurities confirms their presence. The presence of different charge states on two sides of the film (one facing the plasma and another facing the vacuum-chamber wall) and the difference in the IR spectra of these states are established. This can be explained by the process of film formation under the influence of the tokamak plasma.

Radiative transitions in C60 thin films under SR excitation

Abstract Photoluminescent (PL) properties of pure C 60 thin solid films were investigated in the emission range of 1.2–2.4eV over a wide temperature range, under excitation with 36eV photon from the undulator beamline of UVSOR. Degradation of PL intensity of the 1.67eV band was discovered under long-time irradiation in ultra-high vacuum condition and its dose dependence was examined at various ambient conditions. Temperature dependence of PL intensity from 10 K to 300 K exhibited an anomaly at the vicinity of the structural phase transition T c ∼ 250K. Time-resolved decay measurements exhibited the decay components of 1.2±0.1ns and of about 400μs. From the influence of oxygen on degradation of PL intensity, we suppose that the triplet state is highly populated and non-radiative decay process mainly occur.

LUMINESCENCE OF HIGH-TEMPERATURE YTTRIUM-BASED SUPERCONDUCTORS

Luminescense spectra of thin films and single crystals of YBa2Cu3O7−x high-temperature superconductors were measured under optical excitation by synchrotron radiation (E = 10.2 eV) and by electrons (cathodoluminescence) with an energy of 6 keV. It has been shown that in all the spectra the main contribution is made by a blue band with an energy of ≈2.9 eV, which is, apparently, the luminescence inherent to the crystal. The time characteristics of luminescence were measured. It turned out that 80% of all the luminescence requires a very long time (τ > 10−6 s) to reach its final level. A model of luminescence appearance is proposed, which is based on luminescence of oxygen quasi-molecules formed by the decay of electronic excitations (luminescence of self-localized and defect-localized excitons).

Spectroscopy of Homogeneous Deuterated Hydrocarbon Films Redeposited from a T-10 Tokamak Plasma Discharge

Homogeneous deuterated hydrocarbon films redeposited from a deuterium plasma discharge inside the T-10 tokamak vacuum chamber are studied using photoluminescence methods; EXAFS, EPR, and IR spectroscopies; and temperature measurements. The photoluminescence excitation spectra of sp3-sp2 nanostructures of tokamak films are compared with those of sp2 nanostructures of C60 fullerite films. The effect of defect states on photoluminescence and its temperature quenching is discussed. It is concluded that the model of temperature luminescence quenching for homogeneous deuterated tokamak films is similar to that for amorphous a-C:H films.

Some recent Russian studies of hydrogen isotope retention in plasma facing materials

Russian studies of hydrogen isotope retention in plasma facing materials of the International Thermo-nuclear Experimental Reactor included the analysis of carbon–deuterium flakes, formed in the vacuum chamber of the T-10 tokamak, as well as modelling of normal reactor operation conditions and plasma disruptions. The decrease in the [D]/[C] atomic ratio and the decrease in the mass of flakes when these flakes were annealed in air and water steam against temperature were determined. Using Fourier transform infrared reflection spectroscopy, we found that deuterium is accumulated in the flakes only in two states: in the C‒ D2 sp3 deformation modes at 633 and 1090 cm−1 and in the C‒ D2, 3 sp3 stretching modes at 2100–2200 cm−1. In co-deposited Be+D films the [D]/[Be] atomic ratio decreases from 0.15 at 375 K to 0.05 at 575 K. Carbon impurities in the Be+D films slightly increases deuterium retention. The effect of plasma disruptions on deuterium retention in tungsten is described.

Experimentally observed orientation of C 60 F 18 molecules on the nickel single crystal (100) surface

The angular dependence of near edge X-ray absorption fine structure (NEXAFS) spectra has been obtained in the vicinity of carbon and fluorine 1s absorption edges in a monolayer film of polar fullerene fluoride (C60F18) molecules on a Ni(100) substrate. The fine structure of the spectra has been identified according to experimental data via calculations based on the density functional theory, and the angular dependence of the spectra has been explained. The orientations of structural molecular fragments are determined from the angular dependence of the NEXAFS spectra. It is demonstrated that the electric dipole moment of a C60F18 molecule is oriented along the normal to the substrate surface with an accuracy of 5°.