Fourth-generation Synchrotron Research Articles

Development of 200 MeV linac for the SKIF light source injector

The new fourth-generation synchrotron light source SKIF is under development in Novosibirsk, Russia. It consists of a 3 GeV electron storage ring with extremely low emittance, a booster synchrotron, and a linear accelerator. The paper discusses essential aspects of the design of the 200 MeV linear accelerator for SKIF, its main characteristics, and parameters in different operation modes. Description of the linac systems is presented.

Wiggler radiation at a low-emittance storage ring and its usage for X-ray absorption spectroscopy.

A wiggler is a high-power insertion device that was used in the past to produce a smooth wide-band X-ray spectrum. It is widely believed that on low-emittance synchrotrons this X-ray source loses its spatial and spectral homogeneity and therefore becomes less ideal than a scanning undulator. In this paper, we report on experimental and computational studies of an in-vacuum wiggler installed on the first fourth-generation synchrotron MAX IV. We investigate how several physical parameters affect the wiggler spectrum and propose a combination of a few of them that results in significant spectral smoothing. We also examine EXAFS spectra for possible distortions originating from the source imperfection. For this purpose, we scrutinize samples of various homogeneity. We conclude that wigglers are still an appropriate class of insertion devices, also on low-emittance synchrotrons.

Theoretical analysis and experimental evaluation of vibration isolation system with broadband characteristic for laser tracker

High-energy synchrotron radiation source, as a large scientific device, is under construction in Beijing, China. This device is one of the fourth-generation synchrotron radiation sources with the highest brightness in the world. It will provide an important support platform for basic science and engineering science. As a kind of high-precision large-scale measurement equipment, laser tracker is used mainly in high-energy particle accelerator equipment installation, precision poses dynamic measurement and antenna feed dynamic motion precision engineering measurement field. At the construction site of high energy synchrotron radiation source, the laser tracker is often used to calibrate and pre-collimate the high energy source magnet equipment and carry on the tunnel measurement . However, the laser tracker is easily affected by the vibration of the surrounding environment, and the adverse vibration seriously affects its measurement accuracy and even causes the equipment to damage. In order to effectively control the influence of environmental vibration and ensure good static bearing capacity, a broadband vibration isolator for laser tracker is proposed. It is installed in the leg position of the triangular bracket of the laser tracker, which ensures the vibration isolation performance and good bearing capacity. For the above system, the equivalent single freedom nonlinear dynamic differential equation is established, and the steady-state response solution of the broadband isolator is obtained by using the complex variable-average method. The numerical finite element method is used to verify the correctness of the theoretical model and corresponding calculation results. On this basis, the stability of a nonlinear system is analyzed by harmonic balance method, and the influence of key designing parameter <i>K</i><sub>3</sub> on vibration isolation performance is considered. Combined with the complexity of the actual working environment of laser tracker, a variety of typical working conditions are set up for test, including long time static pressure test, vertical impact excitation and lateral displacement excitation tests, to evaluate the static stability and vibration control effect of broadband isolator. The experimental results show that the maximum static displacement of the laser tracker is about 2×10<sup>–5</sup> m under static pressure in a long time, and the maximum static load is within the allowable error range. When the occasional impacting is triggered, the installation of broadband isolator can make the combination quickly restore stability in about 2.95 s, exhibiting better vibration isolation performance. Under different dynamic loads, by comparing the acceleration frequency response curves of the laser tracker with and without the isolator, in the frequency band below the fundamental frequency of the laser tracker, the attenuation rate of the combined system can be up to about 97% with and without the vibration isolator. In the frequency band above the fundamental frequency, the attenuation rate of the combined system with and without the vibration isolation system can reach up to about 88%, and the effective vibration isolation frequency band is extended. The broadband vibration isolator meets all technical requirements.

Lattice optimization of a fourth-generation synchrotron radiation light source in Novosibirsk

We discuss the choice of the magnetic lattice and parameter optimization of the fourth-generation light source SKIF (Russian acronym for Siberian Circular Photon Source) under construction in Novosibirsk. The study compares several basic lattice cells to procure one with low emittance and large dynamic aperture. The result is a developed lattice of SKIF with 72 pm natural emittance (at zero beam current and absent betatron coupling) at 3 GeV beam energy and 476 m circumference. Only two families of sextupoles provide horizontal and vertical dynamic apertures of 12 mm and 3.5 mm, respectively, and energy acceptance more than 5%. To check the potential of the found solution, we used slightly modified SKIF lattice to design 6 GeV light source and reached 33 pm natural emittance for 1075 m circumference with 40 straight sections. Again, only two sextupole families ensure sufficient dynamic aperture (7 mm horizontal and 4 mm vertical) and energy acceptance more than 5% for simple efficient injection and sufficient beam lifetime.

Equilibrium of an arbitrary bunch train with cavity resonators and short range wake: Enhanced iterative solution with Anderson acceleration

This paper continues the work of two previous treatments of bunch lengthening by a passive harmonic cavity in an electron storage ring. Such cavities, intended to reduce the effect of Touschek scattering, are a feature of fourth generation synchrotron light sources. The charge densities in the equilibrium state are given by solutions of coupled Ha\"issinski equations, which are nonlinear integral equations. If the only wake fields are from cavity resonators, the unknowns can be the Fourier transforms of bunch densities at the resonator frequencies. The solution scheme based on this choice of unknowns proved to be deficient at the design current when multiple resonators were included. Here we return to the conventional formulation of Ha\"issinski equations in coordinate space, the unknowns being charge densities at mesh points on a fine grid. This system would be awkward to solve by the Newton method used previously, because the Jacobian matrix is very large. Here a new solution is described, which is both Jacobian-free and much simpler. It is based on an elementary fixed point iteration, accelerated by Anderson's method. The scheme is notably fast and robust, accommodating even the case of extreme over-stretching at current far beyond the design value. The Anderson method is promising for many problems in accelerator theory and beyond, since it is quite simple and can be used to attack all kinds of nonlinear and linear integral and differential equations. Results are presented for ALS-U, with updated design parameters. The model includes harmonic and main r.f. cavities, compensation of beam loading of the main cavity by adjustment of the generator voltage, and a realistic short range wake field (rather than the broad-band resonator wake invoked previously).

Measurement of the coherent beam properties at the CoSAXS beamline.

The CoSAXS beamline at the MAX IV Laboratory is a modern multi-purpose (coherent) small-angle X-ray scattering (CoSAXS) instrument, designed to provide intense and optionally coherent illumination at the sample position, enabling coherent imaging and speckle contrast techniques. X-ray tracing simulations used to design the beamline optics have predicted a total photon flux of 1012-1013 photons s-1 and a degree of coherence of up to 10% at 7.1 keV. The normalized degree of coherence and the coherent flux of this instrument were experimentally determined using the separability of a ptychographic reconstruction into multiple mutually incoherent modes and thus the Coherence in the name CoSAXS was verified. How the beamline can be used both for coherent imaging and XPCS measurements, which both heavily rely on the degree of coherence of the beam, was demonstrated. These results are the first experimental quantification of coherence properties in a SAXS instrument at a fourth-generation synchrotron light source.

Studies on Transverse Resonance Island Buckets in third and fourth generation synchrotron light sources

A Transverse Resonance Island Bucket optics has a betatron tune close to a resonance, such that the particle motion is governed by non-linear terms in the equation of motion. This results in additional stable fixed points in transverse phase-space, which can be populated with a single RF-bunch filling pattern. Thus, these optics have the potential of providing pseudo single-bunch operation, i.e. allows some beamlines to receive light pulses at the revolutionary frequency while the remaining beamlines continue to receive pulses with a frequency set by the ring RF. By blocking either the synchrotron radiation from the standard orbit or secondary orbit each beamline can individually choose whether they want multi- or single-bunch synchrotron radiation. Transverse Resonance Island Bucket optics were achieved in both MAX IV storage rings. In particular, the optics of the 1.5 GeV ring has been characterized both theoretically and experimentally, and we show that TRIBs are achieved in a lattice without any octupolar elements. Furthermore, a feasibility study was performed which indicates that the beamlines of the 1.5 GeV ring could make use of the synchrotron radiation from the island orbit while blocking the standard orbit radiation.

Using low dose x-ray speckle visibility spectroscopy to study dynamics of soft matter samples

We demonstrate the successful application of x-ray speckle visibility spectroscopy (XSVS) experiments to study the dynamics of radiation sensitive, biological samples with unprecedented small x-ray doses of 45 Gy and below. Using XSVS, we track the dynamics of casein micelles in native, concentrated, and acidified solution conditions, while substantially reducing the deposited dose as compared to alternative techniques like sequential x-ray photon correlation spectroscopy. The Brownian motion in a skim milk sample yields the hydrodynamic radius of the casein micelles while deviations from Brownian motion with a characteristic q-dependent diffusion coefficient D(q) can be observed in more concentrated solution conditions. The low dose applied in our experiments allows the observation of static, frozen speckle patterns from gelled acidic milk. We show that the XSVS technique is especially suitable for tracking dynamics of radiation sensitive samples in combination with the improved coherent properties of new generation x-ray sources, emphasizing the great potential for further investigations of protein dynamics using fourth generation synchrotrons and free electron lasers.

Cateretê: the coherent X-ray scattering beamline at the fourth-generation synchrotron facility SIRIUS

Cateretê: the coherent X-ray scattering beamline at the fourth-generation synchrotron facility SIRIUS

Beam heating from a fourth-generation synchrotron source

Beam heating from a fourth-generation synchrotron source

Fourth-generation synchrotron radiation and XFEL facilities: new era in crystallography and materials science

Fourth-generation synchrotron radiation and XFEL facilities: new era in crystallography and materials science

Hard X-ray nanoprobe scanner.

X-ray scientists are continually striving to improve the quality of X-ray microscopy, due to the fact that the information obtained from X-ray microscopy of materials can be complementary to that obtained from optical and electron microscopes. In contrast to the ease with which one can deflect electron beams, the relative difficulty to deflect X-ray has constrained the development of scanning X-ray microscopes (SXMs) based on a scan of an X-ray small probe. This restriction has caused severe complications that hinder progress toward achieving ultimate resolution. Here, a simple and innovative method for constructing an SXM equipped with a nanoprobe scanner is proposed. The nanoprobe scanner combines X-ray prisms and advanced Kirkpatrick-Baez focusing mirrors. By rotating the prisms on the order of degrees, X-ray probe scanning with single-nanometre accuracy can be easily achieved. The validity of the concept was verified by acquiring an SXM image of a test pattern at a photon energy of 10 keV, where 50 nm line-and-space structures were resolved. This method is readily applicable to an SXM with a single-nanometre resolution and will assist effective utilization of increasing brightness of fourth-generation synchrotron radiation sources.

Microsecond hydrodynamic interactions in dense colloidal dispersions probed at the European XFEL.

Many soft-matter systems are composed of macromolecules or nanoparticles suspended in water. The characteristic times at intrinsic length scales of a few nanometres fall therefore in the microsecond and sub-microsecond time regimes. With the development of free-electron lasers (FELs) and fourth-generation synchrotron light-sources, time-resolved experiments in such time and length ranges will become routinely accessible in the near future. In the present work we report our findings on prototypical soft-matter systems, composed of charge-stabilized silica nanoparticles dispersed in water, with radii between 12 and 15 nm and volume fractions between 0.005 and 0.2. The sample dynamics were probed by means of X-ray photon correlation spectroscopy, employing the megahertz pulse repetition rate of the European XFEL and the Adaptive Gain Integrating Pixel Detector. We show that it is possible to correctly identify the dynamical properties that determine the diffusion constant, both for stationary samples and for systems driven by XFEL pulses. Remarkably, despite the high photon density the only observable induced effect is the heating of the scattering volume, meaning that all other X-ray induced effects do not influence the structure and the dynamics on the probed timescales. This work also illustrates the potential to control such induced heating and it can be predicted with thermodynamic models.

Beam heating from a fourth-generation synchrotron source.

The high levels of flux available at a fourth-generation synchrotron are shown to have significant beam heating effects for high-energy X-rays and radiation hard samples, leading to temperature increases of over 400 K with a monochromatic beam. These effects have been investigated at the ID11 beamline at the recently upgraded ESRF Extremely Brilliant Source, using thermal lattice expansion to perform in situ measurements of beam heating. Results showed significant increases in temperature for metal and ceria samples, which are compared with a lumped thermodynamic model, providing a tool for estimating beam heating effects. These temperature increases may have a drastic effect on samples and measurements, such as the rapid recrystallization of a copper wire shown here. These results demonstrate the importance of beam heating and provide information needed to consider, predict and mitigate these effects.

Contrast - a lightweight Python framework for beamline orchestration and data acquisition.

The emergence of fourth-generation synchrotrons is prompting the development of new systems for experimental control and data acquisition. However, asgeneral control systems are designed to cover a wide set of instruments andtechniques, they tend to become large and complicated, at the cost of experimental flexibility. Here we present Contrast, a simple Python framework for interacting with beamline components, orchestrating experiments and managing data acquisition. The system is presented and demonstrated via its application at the NanoMAX beamline of the MAX IV Laboratory.

Removal of spurious data in Bragg coherent diffraction imaging: an algorithm for automated data preprocessing

Bragg coherent diffraction imaging (BCDI) provides a powerful tool for obtaining high-resolution structural information from nanocrystalline materials. Here a BCDI sample consisting of a large number of randomly oriented nanoscale crystals is considered. Ideally, only one crystal is oriented to produce a Bragg peak on the detector. However, diffraction from other crystals often produces additional signals on the detector. Before the measured diffraction patterns can be processed into structural images, scientists routinely need to manually identify and remove the `alien' intensities from sources other than the intended crystal. With the development of modern high-coherence storage rings, such as the upgraded Advanced Photon Source (APS), the already slow process of manual preprocessing will be untenable for the large volumes of data that will be produced. An automated method of identifying and deleting alien intensities is proposed. This method exploits the fact that BCDI of a perfect crystal produces diffraction data with inversion symmetry around the Bragg peak. This approach uses the machine learning clustering method DBSCAN to distinguish between diffraction from multiple sources, and then calculates cluster size and inversion symmetry to assess whether clusters of intensity belong to desired data or alien signals. This approach can dramatically reduce the amount of time spent manually processing data, allowing BCDI data processing capabilities to keep pace with the technological advances of fourth-generation synchrotron light sources.

Equilibrium of an arbitrary bunch train in the presence of multiple resonator wakefields

A higher harmonic cavity (HHC), used to cause bunch lengthening for an increase in the Touschek lifetime, is a feature of several fourth generation synchrotron light sources. The desired bunch lengthening is complicated by the presence of required gaps in the bunch train. In a recent paper the author and Venturini studied the effect of various fill patterns by calculating the charge densities in the equilibrium state, through coupled Ha\"issinski equations. We assumed that the only collective force was from the beam loading (wake field) of the harmonic cavity in its lowest mode. The present paper improves the notation and organization of the equations so as to allow an easy inclusion of multiple resonator wake fields. This allows one to study the effects of beam loading of the main accelerating cavity, higher order modes of the cavities, and short range geometric wakes represented by low-$Q$ resonators. As an example these effects are explored for ALS-U. The compensation of the induced voltage in the main cavity, achieved in practice by a feedback system, is modeled by adjustment of the generator voltage through a new iterative scheme. Except in the case of a complete fill, the compensated main cavity beam loading has a substantial effect on the bunch profiles and the Touschek lifetimes. A $Q=6$ resonator, approximating the effect of a realistic short range wake, is also consequential for the bunch forms.

A wave optics model for the effect of partial coherence on coherent diffractive imaging

With the development of fourth-generation synchrotron sources, coherent diffractive imaging (CDI) will be a mainstream method for 3D structure determination at nanometre resolution. The partial coherence of incident X-rays plays a critical role in the reconstructed image quality. Here a wave optics model is proposed to analyze the effect of partial coherence on CDI for an actual beamline layout, based on the finite size of the source and the influence of the optics on the wavefront. Based on this model, the light field distribution at any plane, the coherence between any two points on this plane and CDI experiments can be simulated. The plane-wave CDI simulation result also shows that in order to reconstruct good image quality of complex samples the visibility of the interference fringes of any two points in the horizontal and vertical directions of the incident light field at the sample needs to be higher than 0.95.

Simultaneous quantitative recognition of all purines including N6-methyladenine via the host-guest interactions on a Mn-MOF

Simultaneous quantitative recognition of all purines including N6-methyladenine via the host-guest interactions on a Mn-MOF

Towards high-quality nitrogen-doped diamond single crystals for X-ray optics.

In this manuscript, characterization of single-crystalline (111) plates prepared from type-Ib diamonds with a nitrogen content of 100-150 ppm by means of high-resolution rocking-curve imaging (RCI) is reported. Contrary to common opinion regarding the intrinsically poor diffraction quality of type-I diamonds, RCI showed the presence of nearly defect-free areas of several millimetres squared in the central part of the diamond plates. The observed broadening of the rocking curves is a result of the cutting and polishing processes, causing strains around the edges of the plates and rare defects. An improvement of the preparation technique will thus allow single-crystalline diamond plates to be made for Laue and Bragg monochromators and beam splitters from type-Ib material with areas large enough to be used as optical elements at fourth-generation synchrotron facilities.