Magnets
Optics
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Open Access
Abstract: In order to generate space for a short, out-of-vacuum multipole wiggler for the DIAD beamline, a single sextupole was removed from one of the DBA arcs in the Diamond Storage Ring during June 2018. The removal of this sextupole presented a number of challenges to the operation of the storage ring, requiring a re-optimisation of the remaining sextupole strengths*, a change in tune-point and modification of the orbit and coupling correction schemes. In this paper we describe the implementation of these changes, and provide an assessment of the impact that the installed wiggler has made on the storage ring parameters.
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Jun 2019
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Optics
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Open Access
Abstract: We pursue Robust Design of a Ring-Based Synchrotron Light Source as a System. In particular, the Design Philosophy is based on: ’ To Control the Nonlinear Dynamics: Control the Linear Optics. In particular, by: ’ Optimal Control of Natural Chromaticity. ’ ’-I Transformer’ between Chromatic Sextupoles for Unit Cell. ’ Higher-Order-Achromat for Super Period. In addition, by pushing the Requirements for Robust & Efficient Injection ’Upstream’, i.e., by considering On-Axis Injection, and by utilizing Reverse Bends (to trans-cend the reductionist Theoretical Minimum Emittance Cell), either: ’ the Natural Emittance can be reduced further, ’ or the Touschek Lifetime can be improved. Bottom line, a Design Choice.
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Jun 2019
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I12-JEEP: Joint Engineering, Environmental and Processing
Optics
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Diamond Proposal Number(s):
[14033]
Open Access
Abstract: High energy X-ray phase contrast tomography is tremendously beneficial to the study of thick and dense materials with poor attenuation contrast. Recently, the X-ray speckle-based imaging technique has attracted widespread interest because multimodal contrast images can now be retrieved simultaneously using an inexpensive wavefront modulator and a less stringent experimental setup. However, it is time-consuming to perform high resolution phase tomography with the conventional step-scan mode because the accumulated time overhead severely limits the speed of data acquisition for each projection. Although phase information can be extracted from a single speckle image, the spatial resolution is deteriorated due to the use of a large correlation window to track the speckle displacement. Here we report a fast data acquisition strategy utilising a fly-scan mode for near field X-ray speckle-based phase tomography. Compared to the existing step-scan scheme, the data acquisition time can be significantly reduced by more than one order of magnitude without compromising spatial resolution. Furthermore, we have extended the proposed speckle-based fly-scan phase tomography into the previously challenging high X-ray energy region (120 keV). This development opens up opportunities for a wide range of applications where exposure time and radiation dose are critical.
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Jun 2019
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Optics
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Abstract: Cr/C multilayer optics are a suitable choice for the tender X-ray range (1–4 keV) that covers the K absorption edges of P, S, Cl and 3d transition metals as well as the L absorption edges of 4d transition metals. In particular, these optics are studied in order to optimize the optical properties of collimated plane-grating monochromators. In this paper, the structure, stress and optical properties of Cr/C multilayers (fabricated using direct-current magnetron sputtering) with bi-layer number of 20 and the same period (about 11.64 nm) but different Cr thickness ratio (0.20–0.80) are investigated. Firstly, the grazing-incidence X-ray reflectivity at 8.04 keV was measured. These measurements were fitted assuming a multilayer structure with a four-layer and non-periodic model. Results and fitting show that interface widths increase with the Cr thickness ratio. The results obtained from X-ray diffraction at 8.04 keV were consistent with high-resolution transmission electron microscopy which showed an increase in grain size of the Cr layers. In addition, the stresses of the Cr/C multilayers have been measured and the results show that the stress value approaches zero when the Cr thickness ratio is about 0.45. The reflectivity of a Cr/C multilayer with Cr thickness ratio of 0.37 was measured and reaches 26.6% at 1.04 keV. The measured reflectivity matches very well with the predicted value using the four-layer and non-periodic model, which confirmed the viability of the prediction. Thus, the reflectivity at 1.04 keV of a Cr/C multilayer with different Cr thickness ratio was predicted and was found to drastically decrease when the Cr thickness ratio is larger than 0.37. It has been determined that a Cr thickness ratio value of 0.37 is the best choice for a Cr/C multilayer in view of high reflectivity and low stress.
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May 2019
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I15-1-X-ray Pair Distribution Function (XPDF)
Optics
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Open Access
Abstract: The Diamond Light Source (DLS) beamline I15-1 measures atomic pair distribution functions (PDF) using scattering of 40-80 keV X-rays. A unique focusing element was needed to condense these X-rays from an initial large cross section (11.0 mm H × 4.2 mm V) into a required spot size of FWHM ≈680 μm (H) × 20 μm (V) at a variable position between the sample and the detector. The large numerical aperture is achieved by coating a silicon substrate over 1 m long with three multilayer stripes of Bragg angle 4.2 mrad. One stripe selects X-rays of each energy 40.0, 65.4, and 76.6 keV. Sixteen piezoelectric bimorph actuators attached to the sides of the mirror substrate adjusted the reflecting surface’s shape. Focal spots of vertical width < 15 µm were obtained at three positions over a 0.92 m range, with fast, easy switching from one focal position to another. Minimized root mean square slope errors were close to 0.5 µrad after subtraction of a uniform curvature. Reflectivity curves taken along each stripe showed consistent high peaks with generally small angular variation of peak positions. This is the first application of a 1 m long multilayer-coated bimorph mirror at a synchrotron beamline. Data collected with its help on a slice of a lithium ion battery’s cathode are presented.
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May 2019
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B16-Test Beamline
Metrology
Optics
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Diamond Proposal Number(s):
[16534]
Open Access
Abstract: X-ray mirrors are widely used in beamlines and laboratories as focusing or collimating optics. As well as the highly accurate processes used to fabricate them, optimized alignment of X-ray mirrors also plays an important role in achieving an ideal X-ray beam. Currently, knife-edge scans are the most often used method for aligning X-ray mirrors, which can characterize the focal size and tune the alignment iteratively. However, knife-edge scanning provides only one-dimensional information and this method suffers from being time-consuming and requiring a high-resolution piezo translation stage. Here we describe a straightforward and non-iterative method for mirror alignment by measuring the relationship between the tilt aberration and the misaligned pitch angle, which is retrieved by an at-wavelength metrology technique using a randomly shaped wavefront modulator. Software and a graphical user interface have been developed to automate the alignment process. Combining the user-friendly interface and the flexibility of the at-wavelength metrology technique, we believe the proposed method and software can benefit researchers working at synchrotron facilities and on laboratory sources.
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Feb 2019
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Metrology
Optics
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Open Access
Abstract: Recently, the dynamic performance of piezo-electric deformable “bimorph” mirrors for synchrotron radiation and X-ray free electron laser sources has been characterized and significantly improved. This innovation enables high intensity X-ray beams to be rapidly focused or defocused to either match to the size of the sample under test or to select different sized regions of interest in larger samples. In this paper, we extend these results by monitoring a bimorph mirror using a combination of ex situ metrology instruments. Comparison between results from the Diamond-NOM (Nanometre Optical Metrology) slope profiler, a Fizeau interferometer, and Zygo ZPSTM distance measuring probes shows that bimorph X-ray mirrors can reliably and accurately be driven at 1 Hz using advanced features recently added to the high voltage (HV), bipolar “HV-Adaptos” power supply from CAEN.
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Feb 2019
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I15-1-X-ray Pair Distribution Function (XPDF)
Optics
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Open Access
Abstract: The X-ray pair distribution function beamline I15-1 at Diamond Light Source requires optical elements that focus a wiggler X-ray beam of high energy (40-80 keV) and large area (11.0 mm × 4.4 mm) into a small spot (FWHM ~ 700 μm (h) × 20 μm (v)) at a variable distance between sample and detector. X-ray lenses do not reach the necessary effective apertures because of absorption and the limits of fabrication technology. The aperture of conventional silicon X-ray mirrors, even with metal coatings, is likewise limited by the shallow critical angle for high-energy X-rays. As a solution, CINEL Strumenti Scientifici delivered the first multilayer-coated bimorph mirror for use at a synchrotron beamline. A silicon substrate was polished by Thales-SESO to have an elliptically curved surface. The mirror was then coated with three multilayer stripes (Ni/B4C, W/B4C, Pt/B4C) of unmatched 1 m length by Rigaku Innovative Technologies. Each stripe’s d-spacing was chosen so that the Bragg angle of its first-order reflection would occur at 4.2 mrad at the center of the mirror. Moreover, each stripe’s d-spacing was graded along the mirror’s length to ensure high reflectivity from the whole stripe. Piezoelectric actuators were then glued to the sides of the coated substrate by Thales-SESO to convert it to a bimorph deformable mirror. This enables the mirror to vary its focusing distance from 3.6 m to 4.8 m, and to compensate for residual long-wavelength slope errors. The mirror’s capability to provide vertical focusing exceeding specifications was demonstrated by ex-situ metrology and in-situ X-ray measurements. Representative results are presented.
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Jan 2019
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Metrology
Optics
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Open Access
Abstract: Nanofocusing compound refractive lenses (CRLs) have short focal lengths and hence require many refracting surfaces to be lined up along the optical axis. The usual spherical or parabolic refracting surfaces introduce aberrations that, in a long CRL, will pile up and lead to unacceptable focal broadening. It has long been known in optics, though not widely in the X-ray synchrotron community, that the ideal lens surface for focusing a point source into a point image lies on a quartic polynomial curve called a Cartesian oval [1]. This is here shown to apply even to the refracting surfaces on the downstream end of a CRL, which accept rays that are already converging toward a focus and bend them toward a new, closer focal point [2]. The following treatment summarizes results recently published [3]. Basic properties of Cartesian ovals will be covered and analytical methods of calculating them will be provided. An “X-ray” approximation of the Cartesian oval will be given for the case of small change in refractive index across the surface, since in this case the general analytical solution becomes numerically unstable. Finally, approximate conic sections will be derived for the paraxial limit. The development of nanofocusing CRLs with large aperture may be guided by these calculations once the technology for fabricating refracting surfaces advances sufficiently.
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Jan 2019
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B16-Test Beamline
Optics
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Open Access
Abstract: With progress towards diffraction limited focusing at third synchrotron sources, obtaining a distortion free wavefront for the X-rays following focusing optics becomes important to enable the exploitation of the high X-ray coherence. We describe a practical method for determining and applying a correction to the wavefront to compensate for distortions caused by fabrication errors in the optics. The method uses custom designed refractive correctors inserted in-line with the optical element. We describe a method for characterising the optics and determining the profile of the refractive corrector and show results from measurements made on real beamline optics.
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Jan 2019
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