Zunping Liu

Single-crystal diamond refractive lens for focusing X-rays in two dimensions

The fabrication and performance evaluation of single-crystal diamond refractive X-ray lenses of which the surfaces are paraboloids of revolution for focusing X-rays in two dimensions simultaneously are reported. The lenses were manufactured using a femtosecond laser micromachining process and tested using X-ray synchrotron radiation. Such lenses were stacked together to form a standard compound refractive lens (CRL). Owing to the superior physical properties of the material, diamond CRLs could become indispensable wavefront-preserving primary focusing optics for X-ray free-electron lasers and the next-generation synchrotron storage rings. They can be used for highly efficient refocusing of the extremely bright X-ray sources for secondary optical schemes with limited aperture such as nanofocusing Fresnel zone plates and multilayer Laue lenses.

Sequential x-ray diffraction topography at 1-BM x-ray optics testing beamline at the advanced photon source

We report progress on implementation and commissioning of sequential X-ray diffraction topography at 1-BM Optics Testing Beamline of the Advanced Photon Source to accommodate growing needs of strain characterization in diffractive crystal optics and other semiconductor single crystals. The setup enables evaluation of strain in single crystals in the nearly-nondispersive double-crystal geometry. Si asymmetric collimator crystals of different crystallographic orientations were designed, fabricated and characterized using in-house capabilities. Imaging the exit beam using digital area detectors permits rapid sequential acquisition of X-ray topographs at different angular positions on the rocking curve of a crystal under investigation. Results on sensitivity and spatial resolution are reported based on experiments with high-quality Si and diamond crystals. The new setup complements laboratory-based X-ray topography capabilities of the Optics group at the Advanced Photon Source.

Diffraction imaging for in situ characterization of double-crystal X-ray monochromators

Imaging of the Bragg reflected x-ray beam is proposed and validated as an in-situ method for characterization of performance of double-crystal monochromators under the heat load of intense synchrotron radiation. A sequence of images is collected at different angular positions on the reflectivity curve of the second crystal and analyzed. The method provides rapid evaluation of the wavefront of the exit beam, which relates to local misorientation of the crystal planes along the beam footprint on the thermally distorted first crystal. The measured misorientation can be directly compared to results of finite element analysis. The imaging method offers an additional insight on the local intrinsic crystal quality over the footprint of the incident x-ray beam.

Simulation and optimization of a sub-micron beam for macromolecular crystallography using SHADOW and XOP at GM/CA CAT at the APS

The small, high intensity and low convergence beams available on beamlines at 3rd generation synchrotron sources have been a boon to macromolecular crystallography. It is now becoming routine to solve structures using a beam in the 5 - 20 micron (FWHM) range. However, many problems in structural biology suffer from poor S/N due to small (a few microns) crystals or larger inhomogenous crystals. In additional, theoretical calculations and experimental results have demonstrated that radiation damage may be reduced by using a micron-sized X-ray beam. At GM/CA CAT we are developing a sub-micron, low convergence beam to address these issues. The sub-micron beam capability will be developed on the existing beamline 23ID-D where the minimum beam size available to users is currently 5 microns in diameter. The target goals are a beam size of ~0.8 micron (FWHM) in diameter, with a beam convergence of less 0.6 milli-rads, a flux greater than 5×1010 photons/sec, and an energy range from 5 to 35 keV. Five optical systems will be compared: 1) a single set of highly demagnifying Kirkpatrick-Baez (K-B) mirrors, 2) multiple Fresnel Zone Plates (FZP), 3) a set of K-B mirrors focusing to a secondary source that is imaged by another set of K-B mirrors, 4) a set of K-B mirrors focusing to a secondary source that is imaged by a FZP, 5) a horizontal focusing mirror focusing to a secondary source that is imaged by another horizontal mirror together with a vertical focusing mirror. Here we will present the results of a design optimization based on ray trace simulations (SHADOW), flux calculations (XOP), and experimental results on 23ID.

Characterization of a bent Laue double-crystal beam-expanding monochromator

A previously reported bent Laue double-crystal monochromator was found to have areas of missing intensity in the final X-ray beam. Measurements of the shape of the bent crystal wafers have been made using mechanical and diffraction methods to evaluate the crystal system and provide insight into potential methods of mitigating the non-uniformities in the beam.

Projection x-ray topography system at 1-BM x-ray optics test beamline at the advanced photon source

Projection X-ray topography of single crystals is a classic technique for the evaluation of intrinsic crystal quality of large crystals. In this technique a crystal sample and an area detector (e.g., X-ray film) collecting intensity of a chosen crystallographic reflection are translated simultaneously across an X-ray beam collimated in the diffraction scattering plane (e.g., [1, 2]). A bending magnet beamline of a third-generation synchrotron source delivering x-ray beam with a large horizontal divergence, and therefore, a large horizontal beam size at a crystal sample position offers an opportunity to obtain X-ray topographs of large crystalline samples (e.g., 6-inch wafers) in just a few exposures. Here we report projection X-ray topography system implemented recently at 1-BM beamline of the Advanced Photon Source. A selected X-ray topograph of a 6-inch wafer of 4H-SiC illustrates capabilities and limitations of the technique.

ANL high‐resolution injector

The ANL (Argonne National Laboratory) high‐resolution injector has been installed to obtain higher mass resolution and higher preacceleration, and to utilize effectively the full mass range of ATLAS (Argonne tandem linac accelerator system). Preliminary results of the first beam test are reported briefly. The design and performance, in particular a high‐mass‐resolution magnet with aberration compensation, are discussed.

Nostradamus and the Synchrotron Engineer: Key Aspects of Predicting Accelerator Structural Response

Multibend Achromat (MBA) synchrotron designs are placing stringent mechanical tolerances on the magnet support systems. At the APS-U the magnet-to-magnet vibration tolerances are about 10 nm. [1]. Timelines, installation requirements, and budgets constrain the resources available for prototyping and physical testing. Reliance on FEA to predict dynamic response is paramount in insuring the tolerances are met. However, obtaining accurate results from a magnet support structure FEA is not as simple as analysing the CAD model of the structure. The 16th century author Nostradamus published a collection of prophecies that since his time, have been held up as predictions of various world events. While it is attractive to think his collection of short poems can be used to foretell the future, in reality it is only the vagueness and absence of any dates that make them easy to apply in a posthoc basis. Arguably, a similar statement can be made about the use of FEA in predicting accelerator support response. In this paper the important contributors to FEA dynamic modelling will be discussed along with techniques that can be used to generate necessary data for models that can accurately predict response.

Establishment of new design criteria for GlidCop® X-ray absorbers

An engineering research program has been conducted at the Advanced Photon Source (APS) in order to determine the thermomechanical conditions that lead to crack formation in GlidCop®, a material commonly used to fabricate X-ray absorbers at X-ray synchrotron facilities. This dispersion-strengthened copper alloy is a proprietary material and detailed technical data of interest to the synchrotron community is limited. The results from the research program have allowed new design criteria to be established for GlidCop® X-ray absorbers based upon the thermomechanically induced fatigue behavior of the material. X-ray power from APS insertion devices was used to expose 30 GlidCop® samples to 10000 thermal loading cycles each under various beam power conditions, and all of the samples were metallurgically examined for crack presence/geometry. In addition, an independent testing facility was hired to measure temperature-dependent mechanical data and uniaxial mechanical fatigue data for numerous GlidCop® samples. Data from these studies support finite element analysis (FEA) simulation and parametric models, allowing the development of a thermal fatigue model and the establishment of new design criteria so that the thermomechanically induced fatigue life of X-ray absorbers may be predicted. It is also demonstrated how the thermal fatigue model can be used as a tool to geometrically optimize X-ray absorber designs.

Studies of single crystal CVD diamonds for potential applications in x-ray crystal optics

Several single crystal CVD diamonds with (001) and (111) surface orientations were studied using x-ray diffraction rocking curve mapping in the double-crystal pseudo plane-wave configuration using Bragg reflection geometry. Strongly nonuniform distributions of rocking curve parameters on the studied crystal surfaces were observed, which indicates that the crystals exhibit substantial lattice distortions. Selected crystal pairs were tested in the nondispersive double-crystal configuration using polychromatic bending magnet synchrotron radiation. The results suggest that CVD diamond crystals could be used as high-flux broadband x-ray monochromators in applications where preservation of the radiation wavefront is not a primary goal.