P. J. Viccaro

Performance of multilayers in intense synchrotron x‐ray beams

The use of multilayer reflectors under intense synchroton x‐ray beams requires to develop a new generation of multilayered materials that can withstand a high‐power load in excess of 100 W/mm2. Multilayers with the high‐Z layer consisting either of a pure element or of compounds such as carbides, nitrides, or silicides have been produced. Because the fabrication conditions are not yet optimized, thin films with satisfactory layer were not obtained leading to poor reflectivities. Such multilayers have been both thermally annealed in a furnace and exposed to a synchrotron beam with a power density of about 1 W/mm2. The resulting damage ranges from the total destruction of the layering to a reduction of the reflectivity by typically 40%–60%. In some cases an only 1%–15% loss in reflectivity has been observed.

Coherent hard x‐ray focusing optics and applications

Coherent hard x‐ray beams with a flux exceeding 109 photons/sec with a bandwidth of 0.1% will be provided by undulators at the third‐generation synchrotron radiation sources such as APS, ESRF, and Spring‐8. The availability of such high flux coherent x‐ray beams offers excellent opportunities for extending the coherence‐based techniques developed in the visible and soft x‐ray part of the electromagnetic spectrum to the hard x‐ray region. These x‐ray techniques (e.g., diffraction‐limited microfocusing, holography, interferometry, phase contrast imaging, and signal enhancement) may offer substantial advantages over noncoherence‐based x‐ray techniques currently used. For example, the signal‐enhancement technique may be used to enhance an anomalous x‐ray or magnetic x‐ray scattering signal by several orders of magnitude. Coherent x rays can be focused to a very small (diffraction‐limited) spot size, thus allowing construction of high spatial resolution microprobes. This paper will discuss the feasibility of e...

Performance of a hard x-ray undulator at CHESS (invited)

A 3.3‐cm period Nd‐Fe‐B hybrid undulator has been designed and successfully operated in the Cornell Electron Storage Ring (CESR). This 2‐m‐long, 123‐pole insertion device is a prototype of one of the undulators planned for the Advanced Photon Source. In dedicated operation, the undulator produced the expected brightness at 5.437 GeV with the fundamental x‐ray energy ranging from 4.3 to 7.9 keV corresponding to a change in gap from 1.5 to 2.8 cm.

X-ray intensity interferometer for undulator radiation

Abstract Intensity interferometry is well established with visible light but has never been demonstrated with X-radiation. We propose to measure the transverse coherence of an X-ray beam using the method of Hanbury Brown and Twiss. The X-ray interferometer consists of an array of slits, a grazing incidence reflective beam splitter, a pair of fast multichannel plate detectors and a broadband, low-noise correlator circuit. The NSLS X1 or X13 soft X-ray undulator will supply the partially coherent X-rays. We are developing this technique to characterize the coherence properties of X-ray beams from high brilliance insertion devices at third-generation synchrotron light facilities such as the Advanced Photon Source and the Advanced Light Source.

The effect of random field errors on the radiation spectra of selected APS undulators

Abstract The effects of the random magnetic field errors are introduced into the calculations of spectral characteristics of tunable undulators for the proposed 7 GeV Advanced Photon Source (APS). Single electron calculations are made for an undulator with first harmonic radiation tunable between 3.5 and 13 keV. Using the universal curves developed by Kincaid [1], the effects of randomly distributed field errors on the first and third harmonics of two proposed typical undulators are calculated. It is found that a lower limit of 0.5% on field errors is more than sufficient for the successful operation of the undulators planned for the APS.

Emittance measurements of CESR using the emitted radiation from a short-period undulator

Abstract The horizontal and vertical emittance of the Cornell Electron Storage Ring (CESR) was measured using the radiation emitted from a short-period (3.3 cm) 123-pole undulator. Average horizontal and vertical emittances measured by this technique were 80 nm-rad and 1.75 nm-rad, respectively. These compare favorably with the results from a charge-coupled device (CCD) system routinely used at CESR and with the calculated values of 65 nm-rad and ∼ nm-rad for the horizontal and vertical emittances respectively.

Modeling the performance of water- and liquid-gallium-cooled X-ray optical components — a comparison with experiment☆

Abstract Thermal and structural analyses of a water- or liquid-gallium-cooled silicon crystal X-ray monochromator subjected to high heat loads have been carried out using a finite-element method. Rocking curves were produced from the computed strain distributions in the crystal and compared with experimentally measured rocking curves. Good agreement between the general width and shape of the calculated and measured rocking curve profiles was obtained. This agreement provides a foundation for extending our modeling to the prediction of X-ray optical component performance with more-complex cooling schemes. Such elaborate cooling techniques may be required for the increased power load that will be produced by insertion devices in the next generation of low-emittance storage ring sources, such as the Advanced Photon Source (APS) to be constructed at Argonne National Laboratory.

Calculation of wiggler spectrum and its absorption in media

Abstract The thermal and structural analyses of beamline and optical components exposed to high heat loads from insertion devices at the third generation synchrotron radiation facilities often require accurate determinations of the absorbed power profile. We have extended the existing PHOTON program (which calculates bending magnet spectra and their absorption in media) to the wiggler regime by taking into account the softening of the energy spectrum as the beam is observed off-axis in the horizontal direction. We describe a model for the wiggler power density and the total power in terms of commonly used parameters. Primarily using Wiggler B at the Advanced Photon Source (APS) as the model source, we find an absorbed power profile in a beryllium window that is markedly different from the power profile of the wiggler source itself: the absorbed power density increases rather than decreases in the horizontal direction. This finding may have a significant impact on the design of windows and other beamline components exposed to high heat load from insertion devices.

Performance analysis of high-power synchrotron x-ray monochromators

Future synchrotron radiation facilities such as the Advanced Photon Source to be constructed at Argonne National Laboratory will produce dedicated and powerful beams ofx-ray radiation instrumental in advanced research in key areas of science, engineering, and medicine. The development nof critical beamline optical components such as monochromators is pivotal in the successful utilization of the generated x-ray beam. The high heat load of the beam can severely distort, and thus nadversely affect the performance of, such components. In this paper, a five-step numerical procedure to predict the performance of an x-ray monochromator nsubjected to high-power synchrotron radiation is described. The predicted performance of a model double-crystal monochromator system expressed in terms of its rocking curves satisfactorily presents the experimental results. This procedure can reliably be used in the design, evaluation, and optimization of monochromators and other optical components.

Soft x‐ray undulator for the U5 beamline at NSLS

The magnetic structure and spectral properties of a 7.5‐cm, 30‐period hybrid undulator are described. The device will be installed at the U5 port of the VUV storge ring at Brookhaven National Laboratory and will be a tunable source of very high brillance soft x‐ray radiation over the range of 13 to approximately 150 eV.