Crystal Monochromator Research Articles

Design and validation of a neutron double crystal monochromator for ICON

Many applications using neutron imaging for materials science use diffraction-based contrast to explore and understand the condition of the samples. Diffraction-based methods require wavelength resolution. The neutron imaging instrument ICON at Paul Scherrer Institut has, until recently, only provided this functionality using a velocity selector. We designed a new double crystal monochromator (DCM) for the conditions at ICON as an option to meet the wavelength resolution demands of specific advanced methods such as diffraction contrast neutron imaging. The DCM can also be combined with the velocity selector. The device uses two pyrolitic graphite crystals as active components, allowing the selection of wavelengths in the interval 2–6 Å. This wavelength interval covers the main applications for wavelength-selective imaging considered at ICON. The device is designed for installation near the instrument shutter system. This position has the advantage that the effective field of view is maximized at the experiment position due to the beam divergence of the ICON. On the other hand, this position means that the beam displacement relative to the initial beam is relatively short. Thus, shielding is vital for the installation. We describe the device design and show the results from the first characterization experiments.

BL09XU: an advanced hard X-ray photoelectron spectroscopy beamline of SPring-8.

The BL09XU beamline of SPring-8 has been reorganized into a beamline dedicated for hard X-ray photoelectron spectroscopy (HAXPES) to provide advanced capabilities with upgraded optical instruments. The beamline has two HAXPES analyzers to cover a wide range of applications. Two sets of double channel-cut crystal monochromators with the Si(220) and (311) reflections were installed to perform resonant HAXPES analyses with a total energy resolution of less than 300 meV over a wide energy range (4.9-12 keV) while achieving a fixed-exit condition. A double-crystal X-ray phase retarder using diamond crystals controls the polarization state with a high degree of polarization over 0.9 in the wide energy range 5.9-9.5 keV. Each HAXPES analyzer is equipped with a focusing mirror to provide a high-flux microbeam. The design and performance of the upgraded instruments are presented.

Towards a wavefront-preservation X-ray crystal monochromator for high-repetition-rate FELs.

The wavefront preservation of coherent X-ray free-electron laser beams is pushing the requirement on the quality and performance of X-ray optics to an unprecedented level. The Strehl ratio can be used to quantify this requirement. In this paper, the criteria for thermal deformation of the X-ray optics are formulated, especially for crystal monochromators. To preserve the X-ray wavefront, the standard deviation of the height error should be sub-nm for mirrors and less than 25 pm for crystal monochromators. Cryocooled silicon crystals combined with two techniques can be used to achieve this level of performance for monochromator crystals: (1) using a focusing element to compensate the second-order component of the thermal deformation; (2)introducing a cooling pad between the cooling block and silicon crystal and optimizing the effective cooling temperature. Each of these techniques allows the thermal deformation in standard deviation of the height error to be reduced by an order of magnitude. As an example, for the LCLS-II-HE Dynamic X-ray Scattering instrument, the criteria on thermal deformation of a high-heat-load monochromator crystal can be achieved for a 100 W SASE FEL beam. Wavefront propagation simulations confirm that the reflected beam intensity profile is satisfactory on both the peak power density and focused beam size.

Performance of small- and wide-angle x-ray scattering beamline at Indus-2 synchrotron

A Small- and Wide-Angle X-ray Scattering (SWAXS) beamline (BL-18) is installed and commissioned at a 1.5 T bending magnet port (5°) of Indus-2 synchrotron at RRCAT, Indore, India. The ∼40-m-long beamline has tunable x-ray energy in the range of 5–20 keV by using a double crystal monochromator. A 1.5-m-long toroidal mirror is used to focus the x-ray beam at the detector position. The beamline is equipped with a 6-m-long movable detector stage to access different wave-vector transfer ranges. At present, an online image plate area detector and a linear position-sensitive gas detector are installed for Small-Angle X-ray Scattering (SAXS) and Wide-Angle X-ray Scattering (WAXS) measurements, respectively. The beamline is operational in simultaneous SAXS/WAXS mode to probe the mesoscopic as well as molecular level structure over a wide range of wave-vector transfer. The specification of the beamline and its performance are reported here. A few recent experimental results, as obtained from BL-18, are also described in brief.

Stability analysis of an angle trimmer mechanism applied to a double crystal monochromator

Double crystal monochromator is the core device of the synchrotron light source beamline, for the application of double crystal monochromator trimmer mechanism not only needs a high angular adjustment resolution, but also needs a high inherent frequency to ensure its stability. In this paper, we have analyzed the inherent frequency of an angle-trimming mechanism applied to a biocrystal monochromator by the energy method, established the relationship equation between its inherent frequency and each parameter of the mechanism, and analyzed the influence of each parameter on its inherent frequency. And we establish the simulation model according to the actual installation situation to carry out finite element analysis. The results prove that the mechanism has excellent stability performance and meets the requirements of light source use.

Concept and strategy of SuperSUN: A new ultracold neutron converter

A new source of ultracold neutrons (UCNs), developed at the Institut Laue-Langevin (ILL) and named SuperSUN, is currently being commissioned. Its operational principle is the conversion of cold neutrons, delivered by ILL’s existing beam H523, to UCNs in a vessel filled with superfluid helium-4, wherein the neutron’s energy and momentum are transferred by inelastic scattering to phonons in the superfluid. The inverse Boltzmann-suppressed process is negligible at temperatures below 0.6 K, enabling long storage times and high in-situ UCN densities as demonstrated at the ILL for two prototype sources. These two prototypes are installed at secondary beams behind crystal monochromators, whereas a primary beam with a white cold spectrum illuminates the SuperSUN conversion volume. This provides not only higher intensity around the wavelength 0.89 nm where the dominant single-phonon process for UCN production takes place, but also a contribution to UCN production by multi-phonon processes. In the first phase of the project, material walls will trap the UCNs, while in the second phase an octupole magnet will generate a 2.1 T magnetic field at the edge of the conversion volume. For low-field-seeking UCNs, this field increases the trapping potential and reduces wall losses so that the accumulated UCNs are spin-polarized as a result. SuperSUN aims to deliver the highest possible UCN densities to external storage experiments, the first of which will be the PanEDM experiment measuring the neutron’s permanent electric dipole moment.

A magnetically controlled chemical-mechanical polishing (MC-CMP) approach for fabricating channel-cut silicon crystal optics for the High Energy Photon Source.

Crystal monochromators are indispensable optical components for the majority of beamlines at synchrotron radiation facilities. Channel-cut monochromators are sometimes chosen to filter monochromatic X-ray beams by virtue of their ultrahigh angular stability. Nevertheless, high-accuracy polishing on the inner diffracting surfaces remains challenging, thus hampering their performance in preserving the coherence or wavefront of the photon beam. Herein, a magnetically controlled chemical-mechanical polishing (MC-CMP) approach has been successfully developed for fine polishing of the inner surfaces of channel-cut crystals. This MC-CMP process relieves the constraints of narrow working space dictated by small offset requirements and achieves near-perfect polishing on the surface of the crystals. Using this method, a high-quality surface with roughness of 0.614 nm (root mean square, r.m.s.) is obtained in a channel-cut crystal with 7 mm gap designed for beamlines at the High Energy Photon Source, a fourth-generation synchrotron radiation source under construction. On-line X-ray topography and rocking-curve measurements indicate that the stress residual layer on the crystal surface was removed. Firstly, the measured rocking-curve width is in good agreement with the theoretical value. Secondly, the peak reflectivity is very close to theoretical values. Thirdly, topographic images of the optics after polishing were uniform without any speckle or scratches. Only a nearly 2.5 nm-thick SiO2 layer was observed on the perfect crystalline matrix from high-resolution transmission electron microscopy photographs, indicating that the structure of the bulk material is defect- and dislocation-free. Future development of MC-CMP is promising for fabricating wavefront-preserving and ultra-stable channel-cut monochromators, which are crucial to exploit the merits of fourth-generation synchrotron radiation sources or hard X-ray free-electron lasers.

X-ray diffraction performance of thermally distorted crystals

Abstract The development of high-brightness X-ray free electron lasers (XFELs), such as hard X-ray self-seeding free electron lasers and XFEL oscillators (XFELOs), brings a severe challenge to the crystal monochromator due to a strong non-uniform thermal load. The distortion caused by spatial temperature gradients can severely affect the optical performance of crystals. Therefore, this paper presents a model to estimate the performance of non-uniform thermally distorted crystals. The model not only takes into account thermal strain, slope error and incident angle deviation, but also considers temperature-dependent factors such as the Debye–Waller factor and electric susceptibility. Our investigation indicates that the Debye–Waller factor reduces the height and bandwidth of rocking curves, and the impact of the electric susceptibility is tiny. The proposed model can describe the distortion of the reflectivity and transmissivity curves of non-uniform thermally loaded crystals and can be applied in the design of crystal monochromators, crystal splitters, crystal compressors and XFELOs.

High-Resolution Three-Axis Neutron Diffractometer for Microstructure Investigations of Polycrystalline Materials

Recently, focusing 3-axis diffractometer set-up equipped with the bent perfect crystal (BPC) monochromator and analyzer which has offered the sensitivity in determination of strains Δd/d < 10−4 in polycrystalline materials, has been introduced. The resolution determined by FWHM of the diffraction profiles is about one order of magnitude higher with respect to that of conventional 2-axis neutron strain/stress scanners. Therefore, the new set-up also offers possibility of line profile analysis for relatively large irradiated gauge volumes and reasonable counting times, because the 3-axis set-up exploits focusing in real and momentum space simultaneously. As it is demonstrated on several samples, the 3-axis diffractometer can be successfully used in the strain/stress measurements on samples exposed to an external load, studies of diffraction profile affected by plastic deformation, determination of phases having very close values of the lattice spacings etc. The analysis is carried out by rocking the BPC analyzer and the neutron signal is registered by a point detector.

Motion control of multi-channel double crystal monochromator based on parallelism error compensation

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Application of adaptive filtering algorithm to the stability problem for double crystal monochromator. Part I: Typical filtering algorithms

The double crystal monochromator (DCM) is one of the critical beamline devices in synchrotron radiation facilities. With the continuous improvement of the performance of the X-ray beamline of synchrotron radiation sources and the constant application of fourth-generation synchrotron radiation sources, higher requirements for the stability of the DCM have been introduced. Based on previous engineering experience, the LN2 cooling system is the most critical factor affecting DCM’s stability. In this paper, the vibration suppression performance of FxLMS (filter-x Least Mean Square), FxNLMS(filter-x Normalized Least Mean Square), FxSDLMS(filter-x Sign-Data Least Mean Square), FxSELMS(filter-x Sign-Error Least Mean Square) and FxSSLMS(filter-x Sign-Sign Least Mean Square) are verified under Bragg@12.66 KeV and Bragg@9 KeV operating conditions for the measured vibration signals of DCM at SSRF(Shanghai Synchrotron Radiation Facility). The results show that the FxNLMS algorithm has higher convergence accuracy, excellent vibration suppression performance, and the ability to counter unknown disturbances compared with other typical filtering algorithms.

Tracking structural phase transitions via single crystal x-ray diffraction at extreme conditions: advantages of extremely brilliant source

Highly brilliant synchrotron source is indispensable to track pressure-induced phenomena in confined crystalline samples in megabar range. In this article, a number of experimental variables affecting the quality high-pressure single-crystal x-ray diffraction data is discussed. An overview of the recent advancements in x-ray diffraction techniques at extreme conditions, in the frame of European Synchrotron Radiation Facility (ESRF)- Extremely Bright Source (EBS), is presented. Particularly, ID15b and ID27 beamlines have profited from the source upgrade, allowing for measurements of a few-micron crystals in megabar range. In case of ID27, a whole new beamline has been devised, including installation of double-multilayer mirrors and double crystal monochromator and construction of custom-made experimental stations. Two case studies from ID27 and ID15b are presented. Hypervalent CsI3 crystals, studied up to 24 GPa, have shown a series of phase transitions: Pnma → P-3c1→ Pm-3 n. First transition leads to formation of orthogonal linear iodine chains made of I3 -. Transformation to the cubic phase at around 21.7 GPa leads to equalization of interatomic I–I distances and formation of homoleptic In m- chains. The second study investigates elastic properties and structure of jadarite, which undergoes isosymmetric phase transition around 16.6 GPa. Despite a few-micron crystal size, twinning and dramatic loss of crystal quality, associated with pressure-induced phase transitions, crystal structures of both compounds have been determined in a straightforward matter, thanks to the recent developments within ESRF-EBS.

Development of monochromators for HEPS

Monochromator plays a key role in the performance of a synchrotron beamline, it determines a beamline’s energy range, bandwidth, flux, focal sizes, coherence, etc., and it has been the limiting optic in a beamline for a long time. Many efforts have been made in order to improve the performance of the monochromators around the world. The HEPS project will need a batch of monochromators and some of them are built in house, many technical problems needed to be solved. A double crystal monochromator prototype has been developed, tested, then modified by improving the mechanical stability, switching to mechanism based on flexures to drive the second crystal. A quick EXAFS Channel-Cut crystal monochromator was designed for the HEPS XAFS beamline, driven by torque motor and closed loop controller. The design aspects and some test results of both monochromators will be introduced. Results show that the design is feasible and meet the requirements of both beamlines.

Design of Tender X-ray Absorption Spectroscopy Beamline in Taiwan Photon Source

A new tender X-ray absorption spectroscopy beamline for operating over the photon energy range from 1.7 keV to 11 keV is under construction at port 32 of the Taiwan Photon Source (TPS). The TPS 32A beamline uses two back-to-back water-cooled double crystal monochromators (DCMs), InSb(111) and Si(111), for achieving the wide energy tunability. The beamline design takes advantage of the low emittance of the TPS accelerator and a bending magnet (BM) to obtain a high-brightness focussed beam. In order to overcome the issue of poor thermal conductivity of InSb(111) crystals while facing high thermal load, we have implemented the following features : (i) we have controlled the flux and heat load by optimizing the source collection angle of 2 × 0.15 mrad2 (h × v), and (ii) we have installed water cooled double-bounce high harmonic rejection mirrors (HHRMs) with a variable incidence angle upstream of the DCM to reduce the heat load on the first InSb crystal. The DCM is followed by a 2:1 toroidal focusing mirror (TFM) which focuses the beam parallel to the floor of the experimental endstation. The simulated focus beam size is 0.9 × 0.9 mm2 (h × v, FWHM) using the InSb(111) DCM at 1.7 keV, and 0.2 × 0.45 mm2 (h × v, FWHM) using the Si(111) DCM at 4 keV, respectively. The photon flux is 1010 -1012 photons s−1 in the energy range of 1.7 to 11 keV at the sample stage after passing through the Be windows. The design parameters of photon flux and beam spot size will facilitate a tender X-ray source for carrying out high-quality X-ray absorption spectroscopy experiments.

Study of a diamond channel cut monochromator for high repetition rate operation at the EuXFEL: FEA thermal load simulations and first experimental results

The recent start of the European X-ray Free-Electron Laser (EuXFEL) provides a unique pulsed X-ray source of high spectral brilliance and high photon flux at a high repetition rate and opens the possibility for new scientific opportunities. However, the EuXFEL beam has a high peak power that is converted into a high cyclic thermal load on the optical elements, such as mirrors and monochromators, and is impossible to fully mitigate within the pulse train pattern. In the single crystal based X-ray monochromators, the increase of temperature leads to deformation of the crystal structure which affects the rocking curve and consequently the performance of these devices and the quality of the transmitted X-ray beam. To address the increase of temperature, we propose the use of a diamond channel-cut monochromator as an alternative to the current silicon monochromators. In this work we present the design and parameters of the diamond monochromator, heat load simulations and the surface and crystalline quality characterisation. The heat load simulations indicate a high performance of the monochromator under the pulse train of the EuXFEL and the characterisation demonstrates high crystal quality and its functionality as a double crystal monochromator.

Demonstration of the X-ray imaging capabilities of the newly installed multilayer monochromator at SPring-8 BL20B2

Double multilayer monochromators (DMMs) for 40 keV and 110 keV have been installed at BL20B2 in SPring-8. The DMMs provide X-rays with a few percent bandwidths at those energies. The flux density of the X-rays is more than several hundred times higher than that of monochromatic X-rays with a silicon double crystal monochromator, which enables us to perform high-speed X-ray imaging with a large field of view and high spatial resolution X-ray imaging in those high-energy X-rays. Here characteristics of DMMs and some demonstrations of X-ray imaging using the high flux density beams are shown.

An experiment demonstrating the capability of a symmetrical layout type double crystal monochromator controlled using electronic cam technology

A demonstration test of a newly developed double crystal monochromator was performed on beamline BL06 in the NewSUBARU synchrotron radiation facility of Hyogo University. Due to the symmetrical layout of the 1st crystal and 2nd crystal units of the monochromator, a maximum rotation speed of the main axis of up to 5.0 degrees/sec could be achieved. The monochromator is controlled by a newly developed control board programmed with an electronic cam algorithm. The control system allows the speed of both Z1 and Z2 axes to be successively synchronized as the Bragg angle changes. The Z 1 and Z 2 axes are moved apart by equal amounts from the center of gravity of the monochromator as the Bragg angle is increased. Also, the speed at which the Z1 and Z2 axes are moved apart increases with larger Bragg angle. This newly developed monochromator can maintain a stable exit beam height just as well as previous mechanical cam type monochromators proved on the height of the exit beam measured by an encoder system and observed by fluorescent screen. Due to the symmetrical layout and newly developed control system, the monochromator is suitable for industrial use because it can handle a wide energy range and allows high-throughput experiments to be carried out.

Spectromicroscopy of Nanoscale Materials in the Tender X-Ray Regime Enabled by a High Efficient Multilayer-Based Grating Monochromator.

The combination of near edge X-ray absorption spectroscopy with nanoscale X-ray imaging is a powerful analytical tool for many applications in energy technologies, catalysis, which are critical to combat climate change, as well as microelectronics and life science. Materials from these scientific areas often contain key elements, such as Si, P, S, Y, Zr, Nb, and Mo as well as lanthanides, whose X-ray absorption edges lie in the so-called tender photon energy range 1.5-5.0keV. Neither conventional grazing incidence grating nor crystal monochromators have high transmission in this energy range, thereby yielding the tender photon energy gap. To close this gap, a monochromator setup based on a multilayer coated blazed plane grating and plane mirror is devised. The measurements show that this novel concept improves the photon flux in the tender X-ray regime by two-orders-of-magnitude enabling previously unattainable laboratory and synchrotron-based studies. This setup is applied to perform nanoscale spectromicroscopy studies. The high photon flux provides sufficient sensitivity to obtain the electronic structure of Mo in platinum-free MoNi4 nanoparticles for electrochemical energy conversion. Additionally, it is shown that the chemical bonding of nano-structures in integrated circuits can be distinguished by the electronic configuration at the Si-K edge.

Characterization of a hard X-ray self-seeding diamond crystal orientation.

We present a method to accurately control the photon energies for hard X-ray Self-seeding schemes with a single crystal monochromator in transmissive geometry. The energy calibration is performed by measuring which pairs of the machine pitch and yaw angles for different crystallographic planes reflect the X-ray at the same wavelength. The free parameters of an analytical formula for the self-seeding energies are determined by fitting the observed intersections and the normalized derivative with respect to the pitch and yaw angles in the observed intersections. The method requires a hard X-ray spectrometer, but it does not rely on its absolute energy calibration. Instead, identifying the self-seeded energies above the SASE background or the monochromatic notches within the SASE bandwidth is sufficient for the calibration.

Pink-Beam Serial Synchrotron Crystallography at Pohang Light Source II

Serial crystallography (SX) enables the determination of room-temperature structures with minimal radiation damage. The photon flux of the pink beam of 1.2% bandwidth (BW) is one order higher than that of the monochromatic beam from a silicon crystal monochromator, and the energy resolution of 1.2% BW is enough to solve the structure; therefore, it is useful to use the pink beam for time-resolved serial synchrotron crystallography (SSX). Here, we demonstrate a pink-beam serial synchrotron crystallographic study at the 1C beamline at the Pohang Light Source II. Lysozyme crystals embedded in a beef tallow injection matrix were delivered through a syringe into the X-ray interaction point. Pink-beam SSX was performed with different X-ray exposure positions to the injection stream (center and edge) and X-ray exposure times (50 and 100 ms). All lysozyme crystal structures were successfully determined at a high resolution of 1.7 Å. Background analysis showed that X-ray diffraction data exposed to the edge of the injection stream could improve the signal-to-noise ratio. All the diffraction data and room-temperature lysozyme structures were comprehensively compared. The data collection strategy and analysis will be helpful in further pink-beam SSX experiments and their applications.