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Most engineering structural metallic alloys are used in polycrystalline form. The nature of the mechanical response of these systems is complex and hierarchical, spanning a range of scales. Lattice strains, distortions and defects (notably, dislocations) nucleate, interact, pile up at grain boundaries and self-organize at the (sub)micrometre scale. Individual grains experience strong interactions with their neighbours and geometric features (cracks, notches). Groups of grains sharing common orientation find themselves embedded within large ensembles possessing certain statistical properties (size distributions, preferred orientation, etc.). Ultimately, the macroscopic properties of grain aggregates are determined by this hierarchy of interactions. Notably, while collective properties such as stiffness are relatively well represented by averages, strength properties associated with fracture, fatigue crack propagation, creep and damage show a strong dependence on the local microscopic conditions of the ‘weakest link’. Ongoing improvements in the spatial resolution of X-ray imaging and tomography and the availability of micro-focused X-ray beams open up a number of opportunities for the study of the structure and deformation at (sub)micrometre scales. Fundamental questions concerning the scale dependence and strain gradient effects in solids can now be tackled by the combination of synchrotron X-ray methods and suitably refined deformation modelling. In this study, a range of methodologies and experimental configurations are presented that have allowed us to develop improved insight into the physical mechanisms of plastic deformation in ductile metallic alloys. Examples include white-beam energy-dispersive diffraction, micro-beam Laue diffraction, scanning micro-beam diffraction topography, high-resolution reciprocal space mapping and imaging. Connections are established with advanced numerical models of polycrystal deformation using strain gradient plasticity and discrete dislocation dynamics modelling.
This paper provides a review of active control strategies used to isolate high-precisionmachines (e.g. telescopes, particle colliders, interferometers, lithography machines or atomic force microscopes) from external disturbances. The objective of this review is to provide tools to develop the best strategy for a given application. Firstly, the main strategies are presented and compared, using single degree of freedom models. Secondly, the case of huge structures constituted of a large number of elements, like particle colliders or segmented telescopes, is considered.
This work includes the creation of a computer model of the superconducting radio frequency cryostat located at the Canadian Light Source (CLS) in Saskatoon, Canada. This cryostat requires careful pressure and level modulation to ensure proper radio frequency control. A detailed mathematical model of the cryostat is generated based on gas and liquid mass balances for a boiling vessel, along with pressure–volume–temperature relations. Model results are compared with experimental data taken from the actual cryostat at the CLS to determine the accuracy of the simulation. Finally, cryostat performance is explored using the model, and it is demonstrated that there are no significant advantages in pressure modulation when reducing the level operating point, and in fact a reduction in operating level slightly increases the maximum value of pressure spikes due to heat loading.
The new synchrotron light source PETRA-III produced its first beam last year. The extremely high brilliance of PETRA-III and the large energy range of many of its beamlines make it useful for a wide range of experiments, particularly in materials science. The detectors at PETRA-III will need to meet several requirements, such as operation across a wide dynamic range, high-speed readout and good quantum efficiency even at high photon energies. PETRA-III beamlines with lower photon energies will typically be equipped with photon-counting silicon detectors for two-dimensional detection and silicon drift detectors for spectroscopy and higher-energy beamlines will use scintillators coupled to cameras or photomultiplier tubes. Longer-term developments include ‘high-Z’ semiconductors for detecting high-energy X-rays, photon-counting readout chips with smaller pixels and higher frame rates and pixellated avalanche photodiodes for time-resolved experiments.
The I13 beamline of Diamond Light Source encompasses two fully independent branches devoted for coherent imaging experiments (coherent X-ray diffraction and ptychography) and X-ray imaging and tomography (full-field microscopy and in-line phase contrast imaging). This contributed paper outlines the main features of the coherence beamline and a preliminary design of the experimental station for coherent X-ray diffraction imaging.
Ground vibration is a key issue for the Shanghai Synchrotron Radiation Facility (SSRF), which is a third-generation light source under commissioning. However, the ground vibration of the SSRF is much larger than other light sources for relatively softer soil and deeper bedrock. More than 1000 piles with 0.6 m diameter down to 48 m underground, and slabs of 1450 mm thickness for the storage ring tunnel and the experiment hall, have been used to attenuate the ground vibration. Measurement results show that these piles and slab have obvious attenuation effect for the vibration induced by nearby vehicles and air conditioners. The coherences with respect to different distances are also carried out.
Beam stability is always a concern in synchrotron light source facilities, and accurate and stable X-ray beam position monitors (XBPM) are key elements in obtaining desired user beam stability. Currently, Advanced Photon Source is preparing to upgrade its facility to increase productivity and to provide better beam stability. For better beam stability, a grazing-incidence insertion device X-ray beam position monitor (GRID-XBPM) is proposed for the insertion device beamline front ends instead of the current photoemission-based XBPM. The design and development of the GRID-XBPM are summarized in this paper including the thermal simulation results of the GRID-XBPM. Thermal and stress analyses show that it withstands the 21 kW total beam power and the peak heat flux of 1684 W mm−2 at a grazing incidence angle of 0.80° using a heat transfer coefficient of 0.010 Wmm−2 °C−1.
Circular dichroism spectroscopy is a useful and versatile tool to obtain low-resolution structural information about proteins, biopolymers and other chiral materials in solution. The first UV–VIS beamline dedicated to circular dichroism, B23, at Diamond Light Source Ltd., a third-generation synchrotron facility in the UK, has recently become operational and is now available for the user community. Herein we summarize the main characteristics of the beamline and some possible applications.
Flexures are enjoying a new boom in numerous high-precision and extreme-environment applications. This paper presents some general aspects of flexure design, showing simple principles, and also some subtler issues concerning kinematic design, stiffness compensation, large reduction ratios and rectilinear as well as circular movements.
Thermal spraying is emerging as the leading route for the deposition of protective coatings onto engineering components to improve operation under extreme conditions of temperature, wear or corrosion. Detailed microstructural assessment is a key element in improving coating performance, and this study demonstrates the application of microfocus X-ray techniques to the determination of elemental and structural variations in the coatings.
Electroluminescent zinc sulfide doped with copper and chloride (ZnS:Cu, Cl) powder was heated to 400°C and rapidly quenched to room temperature. Comparison between the quenched and non-quenched phosphors using synchrotron radiation X-ray powder diffraction (XRPD) (λ = 0.828692 Å) and X-ray absorption spectroscopy (XAS) was made. XRPD shows that the expected highly faulted structure is observed with excellent resolution out to 150° 2θ (or to (12 2 2) of the sphalerite phase). The quenched sample compared to the unheated sample shows a large change in peak ratios between 46.7° and 46.9°, which is thought to correspond to the wurtzite (0 0 6), (0 3 2) and sphalerite (3 3 3)/(5 1 1) peaks. Hence, a large proportion of this sphalerite diffraction is lost from the material upon rapid quenching, but not when the material is allowed to cool slowly. The Zn K-edge XAS data indicate that the crystalline structures are indistinguishable using this technique, but do give an indication that the electronic structure has altered due to changing intensity of the white line. It is noted that the blue electroluminescence (EL) emission bands are lost upon quenching: however, a large amount of total EL emission intensity is also removed, which is consistent with our findings. We report the XRPD of a working alternating-current electroluminescence device in the synchrotron X-ray beam, which exhibits a new diffraction pattern when the device is powered in an AC field even though the phosphor is fixed in the binder. Significantly, only a few crystals are required to yield the diffraction data because of the high flux X-ray source. These in panel data show multiple sharp diffraction lines spread out under the region, where capillary data show broad diffraction intensity indicating that the phosphor powder is comprised of unique crystals, each having different structures.
The storage ring tune measurement system at the Advanced Photon Source (APS) consists of signal pickup and beam excitation drive striplines. Striplines currently installed in the APS storage ring are of a four-blade (inner conductor) design that serves as a beam diagnostic tool and for transverse and longitudinal tune measurements. A new two-blade stripline was designed for the transverse feedback system and to be used for horizontal beam excitation. In this paper, we discuss its mechanical design, assembly procedure, and construction.
One of the multiple capabilities of the new Joint Engineering, Environmental and Processing (JEEP) beamline I12 at Diamond Light Source is the set-up for polychromatic high-energy X-ray diffraction for the study of polycrystalline deformation and residual stresses. The results and interpretation of the first experiments carried out on JEEP are reported. Energy dispersive diffraction patterns from titanium alloy Ti-6Al-4V were collected using the new 23-cell ‘horseshoe’ detector and interpreted using Pawley refinement to determine the residual elastic strains at the macro- and meso-scale. It provides a clear demonstration of the tensile-compressive hardening asymmetry of the hexagonal close-packed grains oriented with the basal plane perpendicular to the loading direction.
Users at the Advanced Photon Source (APS) requested a special purpose undulator that required 456 electromagnetic coils. This paper discusses the design and fabrication techniques used at the APS to build these room-temperature coils. The coils are made from insulated square copper conductor and are vacuum impregnated with epoxy.
The Bi-based oxide superconducting wire is one of the most promising materials for practical uses such as electric power transmission, electromagnets and so on. For the higher performances required in these applications, it is necessary to increase the critical current (Ic). We have carried out synchrotron radiation X-ray diffraction analysis to improve our manufacturing processes and thus to achieve higher Ic. We have performed in situ X-ray diffraction measurements during the sintering and cooling processes, and observed the decrease of Bi-2223(=(Bi,Pb)2Sr2Ca2Cu3Ox) phase during the cooling process. We have also evaluated the distribution of the crystal orientation in whole wire thickness, by measuring the rocking curves. We have observed that the distribution of the crystal orientation is improved by a refinement of the process conditions.
X-ray absorbers in the front ends and beamlines of synchrotron light sources are exposed to very high thermal loads. Many facilities, such as the Advanced Photon Source, are investigating upgrades that will further increase the thermal load. The likelihood of exceeding the limit of subcooled critical heat flux (CHF) in these components was examined. The assessment was performed for both currently possible off-normal operational conditions, such as might occur in the event of a failure of multiple safety interlocks, and the anticipated operating conditions that may result from future upgrades. The subcooled CHF values were calculated using empirical equations frequently cited in the literature and then compared with the computed values of the heat flux at the walls of the component cooling channels in cases where the cooling wall temperature exceeded the water saturation temperature at local hydraulic conditions. Having in mind that the great majority of the available empirical correlations were developed for the conditions characteristic for the operation of heat exchangers in the nuclear power industry, the limitations of this approach are discussed and an experimental study of the subcooled CHF values in the conditions similar to those expected in the front-end and beamline components is proposed.
The limiting factor to the exploitation of the huge photon flux produced by a third-generation synchrotron light source is very often the detector. Experiments in material science often exploit X-ray diffraction. A fast and efficient detection of diffraction patterns enables dynamic experiments. Monolithic active pixel sensors (MAPS) can be exploited effectively to build fast and efficient detectors for X-ray diffraction. For its material science beam lines Diamond Light Source is developing and evaluating detectors based on commercial MAPS and MAPS developed for scientific applications. The various projects, target performance and some experimental results are reported in this paper.
We report the design and construction of an ultrahigh vacuum compatible cryogenic manipulator for angle-resolved photoemission spectroscopy. This design allows six-axis motions in order to measure the band dispersion and Fermi surface of novel electronic materials. Three translational and polar angular motions are implemented by commercial stages. The azimuthal angle of the crystal can be rotated by up to ±90°, and the range of tilt motion varies from 95° to –10°. The sample position is designed at the centre of the above rotation goniometers. The sample holder is cooled using a continuous-flow cryostat. With liquid helium and nitrogen used for the cryostat, the temperature performance of the sample holder is tested and discussed.
We present an X-ray diffraction study of a semiconductor symmetric tilt grain boundary. The theory of crystal truncation rod scattering is extended to bicrystal interfaces and compared with experimental data measured at the Diamond Light Source.
At the Diamond Light Source, adaptive bimorph mirrors are extensively used to focus synchrotron light. Piezo crystals embedded in each bimorph mirror expand or contract in response to applied voltages, enabling the curvature of the reflecting surface to adapt to the required form. However, high-grade metrology tools are needed to determine the optimal voltages. The Diamond Optics & Metrology group have implemented in situ (on the beamlines) and ex situ (in a metrology lab) methods of characterizing optical surfaces. For ex situ tests, a slope-measuring profiler (the Diamond-NOM (Nanometre Optical Metrology)) is employed. In situ, X-ray pencil beam scans, performed using an X-ray sensitive camera and software designed in-house, are used to correct optical slope errors. Ex situ and in situ data are shown to be in good agreement. Examples of in situ improvements in the focusing quality and deliberate defocusing are shown. The methods developed are also applicable to many other forms of adaptive optics.