Showing papers on "Synchrotron radiation published in 1977"
TL;DR: In this paper, a helical wiggler was proposed as an improved source of synchrotron radiation from high-energy electron storage rings, where electrons were made to travel in a short period helix by a transverse helical magnetic field.
Abstract: A new kind of wiggler is proposed as an improved source of synchrotron radiation from high‐energy electron storage rings. The electrons are made to travel in a short‐period helix by a transverse helical magnetic field. The radiation spectrum produced is calculated and it is shown that the helical wiggler design could produce a total intensity (photons sec−1 per unit bandwidth) improvement of several hundred and a brightness (photons sec−1 per solid angle per unit bandwidth) improvement of 4×104 over the present state of the art in synchrotron radiation sources.
220 citations
TL;DR: In this paper, the solution to the equation of transfer of polarized radiation in a steady-state homogeneous rarefied medium is applied to self-absorbed synchrotron sources.
Abstract: The solution to the equation of transfer of polarized radiation in a steady-state homogeneous rarefied medium is applied to self-absorbed synchrotron sources. Relativistic electrons (independent of the presence of any cold plasma) can quite easily produce in such sources significant Faraday rotation and/or conversion of linear to circular polarization. Structural inhomogeneities do not obviate the importance of these phenomena in compact nonthermal sources. Contrary to the calculation of Pacholczyk and Swihart (1975), the circular polarization for a homogeneous source changes sign just below the self-absorption turnover as the source becomes opaque, even when polarization conversion dominates; however, for a physically realistic source, structural inhomogeneity may alter this behavior. The observational evidence bearing upon these effects is reviewed.
196 citations
TL;DR: In this paper, the authors measured the efficiency of diffraction of 45 −275 eV x rays into orders by interferometrically formed, electrodeposited, gold transmission gratings on the 4° beam line at the Stanford Synchrotron Radiation Project (SSRP).
Abstract: Efficiencies for diffraction of 45–275-eV x rays into orders by interferometrically formed, electrodeposited, gold transmission gratings have been measured on the 4° beam line at the Stanford Synchrotron Radiation Project (SSRP). Anomalous dispersion affects the observed efficiency since the gold is partially transmitting to x rays. Model calculations which include anomalous dispersion are in good agreement with observations. With a suitable choice of material and thickness, a grating can be optimized for a given wavelength range by reducing the zero order transmission and enhancing the higher orders. Even orders are suppressed for a grating with equal slit and wire sizes.
101 citations
TL;DR: In this paper, the authors present an LSE abstract of the LSE-ARTICLE-1977-008, which is the only LSE article that discusses the relationship between the two papers.
Abstract: Note: Bell tel labs inc,murray hill,nj 07974.ISI Document Delivery No.: DV770 Reference LSE-ARTICLE-1977-008doi:10.1103/PhysRevB.16.1581 Record created on 2006-10-03, modified on 2017-05-12
89 citations
TL;DR: In this paper, the special features of X-ray energy-dispersive powder and single-crystal diffraction using synchrotron radiation are discussed on the basis of experiments performed at the Deutsches Elektronen-Synchrotor, DESY.
Abstract: The special features of X-ray energy-dispersive powder and single-crystal diffraction using synchrotron radiation are discussed on the basis of experiments performed at the Deutsches Elektronen-Synchrotron, DESY. The method is shown to be of particular value for fast structure identifications, experiments for which large scattering vectors are important, studies of phase transformations and chemical reactions at elevated temperatures and high-pressure studies. Studies of time-dependent phenomena using pulsed external fields are discussed.
71 citations
TL;DR: In this article, a theory of spontaneous radiation of γ-quanta in channeling relativistic particles was developed, which is different from the presently known types of radiation sources.
Abstract: The theory of a new effect is developed — spontaneous radiation of γ-quanta in channeling relativistic particles. The radiation characteristics are different from the presently known types of radiation sources. At energies of the order of 1 GeV the radiation is characterized by wavelength ⪅ 10−3 A. The radiation intensity is about 6 to 9 orders of magnitude higher than obtained from modern synchrotrons. Its monochromaticity is considerably better than bremsstrahlung or synchrotron radiation. The radiation is fairly well polarized. In the quantum treatment, the radiation is caused by transitions between levels, which are formed in channeling in the fields of atomic planes and rows. A classical and quantum calculation of the radiation intensity is presented. At a current of about 100 μA and a target thickness of ≈ 1000 μm, about 1018 to 1019 quanta/s are radiated. The spectral density of the radiation is considerably higher than that of any known kind of radiation. It is suggested that the radiation might be used to influence selectively nuclear transitions and to produce a γ-laser. This radiation can be used to study the crystal lattice potentials, measure the particle energy, and so on. Dispersion is studied. The possibility of enhancing the induced radiation is shown. A number of studies on light channeled particles are analysed.
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63 citations
62 citations
TL;DR: In this paper, a code was developed to calculate the cyclotron radiation spectrum emitted by a slab model tokamak plasma in a direction outward along a major radius, assuming both a thermal and a suprathermal electron component for the plasma, and including the effects of selfabsorption of the radiation by the thermal plasma.
Abstract: A code has been developed which calculates the cyclotron radiation spectrum emitted by a slab model tokamak plasma in a direction outward along a major radius. The calculation assumes both a thermal and a suprathermal electron component for the plasma, and includes the effects of self-absorption of the radiation by the thermal plasma. Various methods are described by which the cyclotron radiation spectrum can be unfolded to obtain parameters of the electron population. A procedure is described by which the electron temperature profile can be obtained from spectral measurements of the cyclotron emission at optically thin frequencies. No absolute calibration of the detection equipment is needed for this method. The code can be used to find parameters of the suprathermal distribution function from its synchrotron emission spectrum, and for the special case of suprathermal electrons at a constant major radius, analytical results are obtained. Finally, the code has been used to calculate cyclotron spectra for various tokamaks: CLEO, TFR, ATC, PLT, and Alcator.
61 citations
TL;DR: In this article, the authors show that at high frequencies the existence of a gradient in the magnetic field causes a gradual bend (a steepening) in the spectrum owing to a decrease in effective source radius with increasing frequency.
Abstract: The time-independent theory of a compact incoherent synchrotron radio source which contains gradients in magnetic field and in relativistic electron distribution is developed and discussed. Analytic expressions for the frequency spectrum are obtained, and we demonstrate the dependence of the spectral index below the synchrotron self-absorption turnover frequency on the gradients in the source and on the source geometry. We show that at high frequencies the existence of a gradient in the magnetic field causes a gradual bend (a steepening) in the spectrum owing to a decrease in effective source radius with increasing frequency. The theoretical interferometric fringe visibility function is computed for a nonuniform source, and it is shown that the characteristic Gaussian angular size derived from this function increases with decreasing frequency below the spectral turnover.We discuss how the important physical parameters of a nonuniform source can be directly derived from observable quantities. The results indicate that the existence of steep gradients in the magnetic field strength and/or the distribution of relativistic electrons can alleviate somewhat the energetic and inverse Compton difficulties of some compact sources, while the presence of moderate gradients only aggravates these problems relative to the homogeneous model.The theory of nonuniform components is applied tomore » the compact radio sources 1633+38 and OQ 172. We find that the radio spectrum of these objects can be interpreted as arising in simple nonuniform sources as opposed to the multiple source models that are necessary when homogeneous components are used. However, the inverse Compton optical and X-ray fluxes in the case of 1633+38 and the predicted minimum angular size in the case of OQ 172 are similar to those obtained via the uniform models.« less
60 citations
TL;DR: In this paper, a transfer procedure based on the coupled-wave formulation was derived, which allows consideration of inhomogeneous sources, and it was shown that plasma characteristic wave eccentricities in a source must be fairly large unless Faraday rotation per absorption depth is very large.
Abstract: As an extension of previous treatments of polarized radiation transfer in homogeneous synchrotron sources, a transfer procedure is derived, based on the coupled-wave formulation, which allows consideration of inhomogeneous sources. It is shown that plasma characteristic wave eccentricities in a source must be fairly large unless Faraday rotation per absorption depth is very large, and that coupling between characteristic waves can be strong in inhomogeneous self-absorbed sources. Calculations are made of the polarized radiation emergent from a source with a boundary of finite thickness. It is found that neglect of propagation effects in the source boundary introduces no significant errors at optically thin frequencies, but that below the self-absorption turnover the emergent polarization may depend significantly upon such effects. In particular, the sign of the circular polarization and the linear polarization position angle depend upon the absorption depth in the boundary region.
58 citations
TL;DR: In this article, the two-dimensional energy-band structure of the layer compound InSe has been determined directly from the polar-angle dependence of its photoemission spectra.
Abstract: The two-dimensional energy-band structure of the layer compound InSe has been determined directly from the polar-angle dependence of its photoemission spectra. The measurements were performed using synchrotron radiation in the photon energy range 15-29 eV. The measuring system consisted of two miniature plane-mirror analyzers which could be moved separately so as to sample electrons in two orthogonal planes, one of which was the plane of incidence. It is demonstrated that the requirements of repeated zone symmetry are rigorously observed. Normal photoemission spectra and effects due to the polarization of the synchrotron radiation are reported and discussed. The experimental energy bands of InSe are found to be in very good agreement with recent pseudopotential calculations on GaSe.
TL;DR: In this paper, a series of hk0 precession photographs were obtained from a crystal of the Fe-containing protein rubredoxin to investigate anomalous scattering effects and study their use in phase determination.
Abstract: The synchrotron X-ray beam produced by the SPEAR storage ring at the Stanford Linear Accelerator Center has been used as a tuneable and intense source for single-crystal-protein diffraction experiments. A measurement of the absolute intensity of a focused, monochromatized X-ray beam gave a value of 3 × 109 photons s-1 at a wavelength of 1.74 A for typical machine operating conditions. A series of hk0 precession photographs were obtained from a crystal of the Fe-containing protein rubredoxin to investigate anomalous scattering effects and study their use in phase determination. Seven discrete wavelengths of radiation were used, some above and some below the Fe K absorption edge (1.743 A = 7.111 keV). The rubredoxin diffraction data showed intensity changes due to f' varying with wavelength as well as from Bijvoet differences. The Fe site could be correctly located from difference Patterson and Fourier maps based either on f' or f”. The signal to noise ratio at the iron site was enhanced by calculating combined f' and f” maps. The phases of the Bragg reflections were also obtained from three films collected at different wavelengths. When compared with the known phases for rubredoxin, the differences average to 60°, which indicates that some phasing information was available even from the relatively poor data and that this method will be potentially useful in future applications. A method for calculating the Lp factor which has to be applied to precession photographs taken with the polarized synchrotron X-ray beam is described in the Appendix.
TL;DR: In this article, the authors investigated the plasmon loss structures produced by the elastic electrons from the Si 2p and Al 2p core levels for different kinetic energies at the elastic electron.
Abstract: Photoelectron spectra of Al and Si have been excited by monochromatized synchrotron radiation at different photon energies. The plasmon loss structures produced by the elastic electrons from the Si 2p and Al 2p core levels have been investigated for different kinetic energies at the elastic electrons. Variation of the plasmon loss intensities for electron kinetic energies of 30–330 eV explains earlier reported absence of plasmon structure in uv photoelectron spectroscopy. The results also indicate that a model of extrinsic bulk plasmon excitation developed by Mahan and modified to account for surface effects could explain the observed threshold behavior of bulk plasmon intensity at low electron kinetic energies.
TL;DR: In this article, the authors present an LSE-related paper, PhysRevB, which is based on the LSE's article "Articles 1977-003" (LSE-ARTICLE-1977-003).
Abstract: Note: Bell tel labs inc,murray hill,nj 07974.ISI Document Delivery No.: DE285 Reference LSE-ARTICLE-1977-003doi:10.1103/PhysRevB.15.3844 Record created on 2006-10-03, modified on 2017-05-12
TL;DR: In this article, the predicted electronpositron pair production in the Crab pulsar outer magnetosphere at the ''outer gap,'' 3 x 10/sup 7/ cm from the neutron star, is considered as a source of pulses at all observed energies.
Abstract: The predicted electron-positron pair production in the Crab pulsar outer magnetosphere at the ''outer gap,'' 3 x 10/sup 7/ cm from the neutron star, is considered as a source of pulses at all observed energies. A pulse and interpulse that are roughly symmetric with separation somewhat less than 180/sup 0/ are expected for arbitrary angles between the stellar magnetic moment and spin. The model gives optical and X-ray pulses from inverse Compton scattering of radio photons by e/sup +/ and e/sup -/ that are created with ..gamma../sub parallel3/ and ..gamma../sub perpendicular4/ relative to B. The Compton boosting occurs during the time before synchrotron radiation reduces ..gamma../sub perpendicular/to below approx.2. The lower-energy pulsed X-ray polarization is predicted to be similar to the optical pulse polarization. The synchrotron radiation gives very hard X-rays and ..gamma..-rays up to 10/sup 3/ MeV. The Crab radio emissions, except for the precursor, are also predicted to originate from the ''outer gap.'' Because of the much weaker magnetic fields near the light cylinder in much slower pulsars, significant Compton boosting and radio emission within the outer gap are possible only in the fastest pulsar with parameters similar to those of the Crab.
TL;DR: In this article, techniques of focusing and monochromating the x radiation from a synchrotron source were discussed. And the properties of non-focusing and focusing x-ray optics were discussed with emphasis on the advantages of each.
Abstract: Techniques of focusing and monochromating the x radiation from a synchrotron source will be discussed. Phase‐space techniques, widely used in charged‐particle beam transport, will be applied to describe the source and optical elements ni the focusing systems. The properties of focusing and nonfocusing x‐ray optics will be presented with emphasis on the advantages of each.
TL;DR: In this article, angle-resolved photoemission (ARP) spectra from polycrystalline copper single crystals were used to demonstrate the importance of the Debye-Waller factor in photo-emission, leading to a breakdown of the direct transition model.
Abstract: With the advent of synchrotron radiation in the 32-280 eV range at the Stanford Synchrotron Radiation Project, it has become possible to elucidate the transition from ultraviolet to X-ray-induced photoemission. This has been accomplished by studies of noble metals. Polycrystalline copper shows a valence-band (VB) profile that approaches the X-ray induced shape at hv ~ 100 eV. In polycrystalline silver, the 4d cross section follows the atomic curve, with a reversal of VB peak intensities near hv = 110 eV. Strongly anisotropic behavior is observed in copper single crystals, using angle-resolved photoemission (ARP). Normal ARP spectra from Cu(100), (110), and (111) crystals follow the band dispersion through the Brillouin Zone, including a dramatic resonance between the Fermi level (EF) and 2 eV binding energy for hv = 43-52 eV. High temperature and high photon energy studies demonstrate the importance of the Debye-Waller factor in photoemission leading to a breakdown of the direct transition model. In adsorption studies of CO on Ni and Pt, CO is shown to stand up with oxygen out. For Pt, electrons are found to flow from t2g orbitals near EF to CO, and the CO 1π and 5σ binding energies are reversed relative to the gas phase. At higher photon energies, hv = 150 eV, the CO orbitals are very prominent on a Pt substrate. An inversion of the angular distribution of these orbitals and energy-dependent resonances in their intensities provide evidence for final state scattering effects at photon energies above 40 eV.
TL;DR: The contrast of dislocations in X-ray topographs taken in the Guinier-Tennevin mode with synchrotron radiation has been studied in this article.
Abstract: The contrast of dislocations in X-ray topographs taken in the Guinier–Tennevin mode with synchrotron radiation has been studied. In reflections where high orders were insignificant, dislocation images appeared very similar to those in Lang topographs taken with characteristic radiation. At large specimen-to-plate distances orientation contrast is important in the direct image. The sense of the Burgers vector of dislocations showing double contrast can be deduced.
TL;DR: In this article, the orientation dependence of the Extended X-ray Absorption Fine Structure (EXAFS) spectrum of single crystal zinc was studied and the spectrum was found to be markedly anisotropic.
TL;DR: A review of existing techniques of crystal assessment by X-ray diffraction topography is described in this article. But this review is limited to a single crystal and polycrystalline material.
TL;DR: An X-ray focusing monochromator for small-angle diffraction studies was designed for use with the synchrotron radiation from the storage ring, SPEAR, at the Stanford Linear Accelerator Center as discussed by the authors.
Abstract: An X-ray focusing monochromator for small-angle diffraction studies was designed for use with the synchrotron radiation from the storage ring, SPEAR, at the Stanford Linear Accelerator Center. It incorporates a 7 cm long silicon crystal, cut at 8°30′ to the (111) planes and bent to a logarithmic spiral curvature for horizontal focusing and monochromatization. A 120 cm long elliptically curved float-glass mirror is used for vertical focusing, and provides means of eliminating higher-order harmonics of smaller wavelength. With SPEAR operating at 3.7 GeV, 20 mA, the two elements produce a 0.5 × 0.5 mm focused beam with an intensity of 6 × 108 photons s−1. The diffraction pattern of frog sciatic nerve myelin obtained with this system was compared with that obtained with a 300 W conventional microfocus X-ray source and a toroidal camera. The new system shows a 190-fold gain in the integrated intensity on photographic film. Synchrotron radiation provides a broad X-ray spectrum. The monochromator is tunable to any wavelength between 0.5 and 3 A, with a total wavelength spread in the focused beam of about 0.01 at 1.74 A. The broad spectrum allows wavelength selection for anomalous-scattering experiments.
Journal Article•
TL;DR: In this article, the design, construction and use of a low-angle X-ray scattering camera involving synchrotron radiation at NINA is described, where the main components of the camera are a horizontally focusing monochromator and a pair of totally reflecting, vertically focusing mirrors.
Abstract: The design, construction and use of a low-angle X-ray scattering camera involving synchrotron radiation at NINA are described. The main components of the camera are a horizontally focusing monochromator and a pair of totally reflecting, vertically focusing mirrors. The camera components are located on a rigid optical bench.
TL;DR: In this paper, a review discusses the research and technological potential of contemporary sources of synchrotron radiation, and a comparison is made of various sources of ultraviolet and x radiation.
Abstract: The review discusses the research and technological potential of contemporary sources of synchrotron radiation. A comparison is made of various sources of ultraviolet and x radiation. Characteristics are given of present electron storage rings—the principal sources of synchrotron radiation, and the means and limits of their further refinement are discussed. The features of performing experiments with synchrotron radiation in storage rings are considered. The main formulas characterizing the properties of synchrotron radiation are presented in a form convenient for practical calculations. The regions of application of synchrotron radiation are discussed (x-ray microscopy, x-ray structural analysis, and molecular, atomic, and nuclear spectroscopy). The principal attention is given to those questions in which the use of synchrotron radiation opens new possibilities. The prospects for practical application of synchrotron radiation are discussed (metrology, medicine, materials science, radiation technology).
TL;DR: In this paper, Angle-resolved UPS, combined with the continuum and polarization properties of synchrotron radiation, has been used to provide experimental evidence for three-dimensional band structure, surface states, and electronic and geometric properties of adsorbed species.
Abstract: Ultraviolet photoemission spectroscopy (UPS) has been developed into an important tool in the study of solid surfaces and adsorbed over‐layers. Until recently, several important parameters in the photoemission process have been, at best, only imperfectly under the control of the experimenter. These are (1) photon energy, (2) optical polarization, and (3) momentum of the emitted electrons. Such limitations have concealed much information implicit in the flux of photoemitted electrons. Angle‐resolved UPS, combined with the continuum and polarization properties of synchrotron radiation, lifts these limitations to a large degree, and provides experimental evidence for three‐ and two‐dimensional band structure, surface states, and electronic and geometric properties of adsorbed species. We show some results of such experiments for clean and chemisorbed W. The data show a variable degree of complexity and, in general, may be analyzed only in the context of specific calculations.
TL;DR: In this article, the integrated reflection intensities were measured on 222, 3\bar 3/bar 3 and \bar 5\bar 5/bar 5 reflections from a GaAs single-crystal plate in the energy region very near the Ga K absorption edge.
Abstract: By the use of synchrotron radiation at Stanford, the integrated reflection intensities were measured on 222, \bar 3\bar 3\bar 3 and \bar 5\bar 5\bar 5 reflections from a GaAs single-crystal plate in the energy region very near the Ga K absorption edge. The energy dependence of the intensities agreed reasonably with the corresponding calculated curves.
TL;DR: In this paper, the conditions in which a charged particle in an inhomogeneous magnetic field (particularly at the edges of a "long" uniform magnet or in a "short" magnet) can emit synchrotron radiation with a spectrum extending beyond the critical frequency were studied.
TL;DR: In this paper, a method for computing the spectral emissivity of spontaneous synchrotron radiation is discussed and the Klimontovich formalism in plasma kinetic theory is adopted in which an ensemble average of the microscopically emitted power is considered.
Abstract: A method for computing the spectral emissivity of spontaneous synchrotron radiation is discussed. The Klimontovich formalism in plasma kinetic theory is adopted in which an ensemble average of the microscopically emitted power is considered. The present method clarifies the meaning of the random phase approximation which is imposed in several existing theories of synchrotron radiation. Both the effects of dielectric polarization and two‐particle correlations are included in the present discussion. The theory is applied to the case of a plasma in thermal equilibrium, for which it is shown that the effect of pair correlations on the emissivity vanishes. On the other hand, the effect of dielectric polarization is studied numerically for a wide range of parameters.
TL;DR: In this paper, the angular distribution parameters of photoelectrons emitted from the 4p shell of krypton by synchrotron radiation were measured and an empirical pseudopotential was derived.
Abstract: New measurements of the angular distribution parameter beta 4p(E) for photoelectrons emitted from the 4p shell of krypton by synchrotron radiation are reported. Analyses of these data produce an empirical pseudopotential together with predictions of beta 4p(E) and the total cross sections sigma 4p(E) for photoelectron energies from threshold to greater than 100 eV. The predicted cross sections are compared with recent experimental data obtained at the Synchrotron Radiation Facility on the Daresbury Laboratory 5 GeV electron synchrotron NINA. Both beta 4p(E) and sigma 4p(E) are well described by both RPAE and pseudopotential theories, suggesting that the latter aptly mimics the exchange and correlation effects throughout the range of observation.