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The ability to freely control the polarization of X-rays enables measurement techniques relying on circular or linear dichroism, which have become indispensable tools for characterizing the properties of chiral molecules or magnetic structures. Therefore, the demand for polarization control in X-ray free-electron lasers is increasing to enable polarization-sensitive dynamical studies on ultrafast time scales. The soft X-ray branch Athos of SwissFEL was designed with the aim of providing freely adjustable and arbitrary polarization by building its undulator solely from modules of the novel Apple X type. In this paper, the magnetic model of the linear inclined and circular Apple X polarization schemes are studied. The polarization is characterized by measuring the angular electron emission distributions of helium for various polarizations using cold target recoil ion momentum spectroscopy. The generation of fully linear polarized light of arbitrary angle, as well as elliptical polarizations of varying degree, are demonstrated.

The ability to freely control the polarization of X‐rays enables measurement techniques relying on circular or linear dichroism, which have become indispensable tools for characterizing the properties of chiral molecules or magnetic structures. Therefore, the demand for polarization control in X‐ray free‐electron lasers is increasing to enable polarization‐sensitive dynamical studies on ultrafast time scales. The soft X‐ray branch Athos of SwissFEL was designed with the aim of providing freely adjustable and arbitrary polarization by building its undulator solely from modules of the novel Apple X type. In this paper, the magnetic model of the linear inclined and circular Apple X polarization schemes are studied. The polarization is characterized by measuring the angular electron emission distributions of helium for various polarizations using cold target recoil ion momentum spectroscopy. The generation of fully linear polarized light of arbitrary angle, as well as elliptical polarizations of varying degree, are demonstrated. [ABSTRACT FROM AUTHOR]

One of the challenges facing modern free-electron laser (FEL) facilities is the accurate pulse-to-pulse online measurement of the absolute flux of the X-ray pulses, for use by both machine operators for optimization and users of the photon beam to better understand their data. This manuscript presents a methodology that combines existing slow-measurement methods currently used in gas detectors across the world and fast uncalibrated signals from multipliers, meant for relative flux pulse-to-pulse measurements, which create a shot-to-shot absolute flux measurement through the use of sensor-based conditional triggers and algorithms at SwissFEL.

One of the challenges facing modern free-electron laser (FEL) facilities is the accurate pulse-to-pulse online measurement of the absolute flux of the X-ray pulses, for use by both machine operators for optimization and users of the photon beam to better understand their data. This manuscript presents a methodology that combines existing slow-measurement methods currently used in gas detectors across the world and fast uncalibrated signals from multipliers, meant for relative flux pulse-to-pulse measurements, which create a shot-to-shot absolute flux measurement through the use of sensor-based conditional triggers and algorithms at SwissFEL. [ABSTRACT FROM AUTHOR]

The successful development in the last two decades of X-ray free electron lasers (FELs) with their revolutionary brightness performance has been tightly dependent on the parallel development of electron guns and injectors capable of providing the high-brightness electron beams required by FELs lasing at these short wavelengths. The ultimate brightness delivered by a linear accelerator (linac) is already set at its injector and the remaining part of the accelerator can be only designed to preserve the injector performance. The technology to be used for the accelerator part of an X-Ray FEL strongly depends on the duty-cycle at which the FEL operates. Normal-conducting, room-temperature, copper-based radio frequency (RF) technology is typically used for low duty-cycles of up to approximately 10−3. For higher duty-cycles and up to continuous wave (CW) operation, the linac must rely on superconductive RF technology because, with the higher duty-cycle, the increasingly higher power dissipated in normal conducting RF structures becomes excessive for the warm technology. The situation changes in the lower energy part of the accelerator, where injector schemes, based on direct current, normal-conducting, and superconducting RF electron guns, are demonstrating the beam quality performance required by high-duty-cycle X-ray FELs. In this paper we start with a description of the requirements for such injectors, followed by an overview of the pursued technologies and schemes, and by a discussion on the main differences in terms of beam dynamics between low and high duty-cycle injectors.

Günümüzde itibari para borçları ödenirken enflasyonun dikkate alınmasının gerekip gerekmediği hususunda görüş ayrılığı bulunmaktadır. Enflasyonun dikkate alınması gerektiği görüşünü savunanlar, çoğunlukla İmam Ebû Yûsuf’un fels borçlarında dirhem değeri üzerinden ödeme yapılması gerektiği yönündeki görüşünü kaynak göstermektedirler. Onlara göre günümüzdeki itibari paralar, felslerle aynı hükümdedir. Enflasyonun dikkate alınmasına karşı çıkanlar ise itibari paraların İmam Ebu Yusuf’un görüşünün kapsamına dahil edilemeyeceği kanaatindedirler. Tartışma büyük ölçüde günümüzdeki itibari paraların İmam Ebu Yusuf’un görüşünün kapsamına dahil olup olmadığı konusundaki belirsizlikten kaynaklanmaktadır. Dolayısıyla tartışmaya katkı sunabilmek için İmam Ebu Yusuf’un görüşünün illeti ve kapsamının ne olduğunu belirlemek büyük önem taşımaktadır. Bu araştırmanın temel hedefi, İmam Ebu Yusuf’un görüşünün illetini tespit ederek görüşün kapsamını net bir biçimde ortaya koymaktır. Hedefin gerçekleştirilebilmesi amacıyla öncelikle klasik fıkıh literatüründe İmam Ebu Yusuf’un görüşünün kapsamıyla ilgili ortaya konulan görüşler ayrı ayrı incelenmiştir. Bu görüşler ışığında hükmün illetinin ve kapsamının ne olduğu ve son olarak günümüzdeki itibari paraların kapsama dahil edilip edilemeyeceği hakkında bir sonuca ulaşılmaya çalışılmıştır. İmam Ebû Yûsuf’un görüşünün borcun sebebi ve konusu bakımından kapsamı hakkında klasik dönemde çeşitli görüşler ortaya konulmuştur. Borcun sebebi bakımından kapsamı, Hanefi mezhebindeki hâkim kanaate göre satım akdi ve karzla sınırlıdır. Kimi çağdaş araştırmacıların tespitlerinin aksine, sebebi gasp ve itlaf olan borçlar, kapsama dahil değildir. Borcun konusu bakımından kapsamı, Ebussuûd el-Mısri gibi kimi Hanefî bilginlere göre, fels borçlarıyla sınırlıdır. İbn Âbidîn ise felslerin yanında bir de katkı oranı yüksek mağşuş paraların kapsama dahil olduğu görüşündedir. Bu itibarla başta Ömer Nasuhi Bilmen olmak üzere kimi çağdaş araştırmacıların veznî ve keylî mal borçlarının kapsama dahil olduğu yönündeki yaklaşımları isabetli değildir. İtibari paraları enflasyon konusunda felslerle aynı hükümde görenler, İmam Ebû Yûsuf tarafından diğer paralardan farklı olarak özellikle fels borçlarında dirhem değerinin dikkate alınmasının, felslerin para olarak yaratılmamış olmasından kaynaklandığını düşünmektedirler. Hâlbuki para olarak yaratılmamış olma özelliği, enflasyonun dikkate alınması gerektiği yönündeki hükme münasib olmadığı gibi hükme tesir eden bir vasıf da değildir. Nitekim hükme tesiri olsaydı, söz gelimi karz olarak verilen buğday borcunda ya da sebebi gasb olan fels borçlarında aynı hükmün geçerli olması gerekirdi. Fels borçlarında enflasyonun dikkate alınıp ödemenin dirhem değeri üzerinden yapılması, felslerin o dönemdeki asıl para birimi olan dirhemlerin küsuratını tamamlayan bozuk paralar olmalarından kaynaklanmaktadır. Bir başka ifadeyle fels borçlarında enflasyonun dikkate alınıp ödemenin dirhem değeri üzerinden yapılmasının sebebi, felslerin dirhem değeri üzerinden işlem gören yardımcı paralar olmalarıdır. Felslerin dirhemlerin küsuratını tamamlayan yardımcı para olarak kullanılmaları, onların dirhem değeri üzerinden işlem gördükleri tespitini yapmaya imkân vermektedir. Öte yandan İmam Ebû Yûsuf’a göre fels borçları ödenirken dinar ya da başka bir mal değerinin değil özellikle dirhem değerinin esas alınması, o dönemde felslerin dirhem değeri üzerinden işlem gördüğünü net bir biçimde göstermektedir. Belirlenen bu illet hükme münasib ve hükme tesir eden bir vasıf olduğu için fels borçlarında ödemenin neden dinar ya da başka bir mal değeri üzerinden değil de dirhem değeri üzerinden yapıldığı izah edilebilmekte ve karz olarak verilen buğday borçlarında ya da sebebi gasb olan fels borçlarında aynı hükmün geçerli olmamasının sebebi ortaya çıkmaktadır. Ayrıca birçok Hanefî fıkıh eserinde İmam Ebû Yûsuf’un görüşünden hiç söz edilmemesi, felslerin dönem dönem asli para birimi haline gelmesiyle izah edilebilmektedir. Günümüzde asli para birimi olarak kullanılan itibari para borçlarında enflasyonun dikkate alınması gerektiği görüşünü savunanların, İmam Ebû Yûsuf’un felslere özgü görüşünü kaynak göstermeleri isabetli değildir.

In this work, we report on incorporating for the first time tree-algorithm based solvers into the molecular dynamics code, XMDYN. XMDYN was developed to describe the interaction of ultrafast X-ray pulses with atomic assemblies. It is also a part of the simulation platform, SIMEX, developed for computational single-particle imaging studies at the SPB/SFX instrument of the European XFEL facility. In order to improve the XMDYN performance, we incorporated the existing tree-algorithm based Coulomb solver, PEPC, into the code, and developed a dedicated tree-algorithm based secondary ionization solver, now also included in the XMDYN code. These extensions enable computationally efficient simulations of X-ray irradiated large atomic assemblies, e.g., large protein systems or viruses that are of strong interest for ultrafast X-ray science. The XMDYN-based preparatory simulations can now guide future single-particle-imaging experiments at the free-electron-laser facility, EuXFEL. [ABSTRACT FROM AUTHOR]

Assessment of rock as a fastening foundation for post‐installed fastenings with shallow embedment depths For rock as a base material for post installed anchors, it is difficult to draw conclusions about the load‐bearing behavior and capacity in advance due to the large number of possible installation parameter. This technical article therefore examines how post‐installed anchors with low embedment depths behave in rock and which rock parameters have a significant influence on the load‐bearing behavior and capacity. For this purpose, tests on anchors with different operating principles (injectable adhesive anchor, mechanical bolt anchor) in different geologies in Eastern Austria were performed. It could be shown that rock classification can be used to infer the suitability of a rock as a base material, but a small‐scale investigation also is necessary to estimate the load‐bearing capacity. Not only the presence of joints has an influence on the load‐bearing capacity, but also the joint condition. Certain analogies to cracked concrete could be shown. [ABSTRACT FROM AUTHOR]

In this work, we analyze the application of X-ray diffraction imaging techniques to follow ultrafast structural transitions in solid materials using the example of an X-ray pump–X-ray probe experiment with a single-crystal silicon performed at a Linac Coherent Light Source. Due to the spatially non-uniform profile of the X-ray beam, the diffractive signal recorded in this experiment included contributions from crystal parts experiencing different fluences from the peak fluence down to zero. With our theoretical model, we could identify specific processes contributing to the silicon melting in those crystal regions, i.e., the non-thermal and thermal melting whose occurrences depended on the locally absorbed X-ray doses. We then constructed the total volume-integrated signal by summing up the coherent signal contributions (amplitudes) from the various crystal regions and found that this significantly differed from the signals obtained for a few selected uniform fluence values, including the peak fluence. This shows that the diffraction imaging signal obtained for a structurally damaged material after an impact of a non-uniform X-ray pump pulse cannot be always interpreted as the material's response to a pulse of a specific (e.g., peak) fluence as it is sometimes believed. This observation has to be taken into account in planning and interpreting future experiments investigating structural changes in materials with X-ray diffraction imaging. [ABSTRACT FROM AUTHOR]

Short wavelength Free-Electron Lasers (FELs) are among the newest light sources available to scientists to probe a wide range of phenomena, with chemical, physical and biological applications, using soft and hard X-rays. These sources include the currently most powerful hard X-ray light sources in the world and are characterized by extremely high powers and high transverse coherence, but the first FELs had, and many still have, reduced longitudinal coherence. Now it is possible to achieve good longitudinal coherence (narrow bandwidth in the frequency domain) and here we discuss and illustrate a range of experiments utilizing this property, and their underlying physics. The primary applications are those which require high resolution (for example resonant experiments), or temporal coherence (for example coherent control experiments). The currently available light sources extend the vast range of laboratory laser techniques to short wavelengths. [ABSTRACT FROM AUTHOR]

Lawrence Berkeley National Laboratory (LBNL) is developing design concepts for a multi-beamline soft xray FEL array powered by a superconducting linear accelerator, operating with a high bunch repetition rate of approximately one MHz. Electron bunches supplied by a high-brightness, high-repetition-rate photocathode electron gun are distributed by a beam spreader, designed to deliver individual bunches from a CW linac to an array of independently configurable FEL beamlines with nominal bunch rates up to 100 kHz in each FEL, and with even pulse spacing. We describe recent developments in the technical choices, design and parameters of thespreader system and its main components.

Liquid microjets are a common means of delivering protein crystals to the focus of X-ray free-electron lasers (FELs) for serial femtosecond crystallography measurements. The high X-ray intensity in the focus initiates an explosion of the microjet and sample. With the advent of X-ray FELs with megahertz rates, the typical velocities of these jets must be increased significantly in order to replenish the damaged material in time for the subsequent measurement with the next X-ray pulse. This work reports the results of a megahertz serial diffraction experiment at the FLASH FEL facility using 4.3 nm radiation. The operation of gas-dynamic nozzles that produce liquid microjets with velocities greater than 80 m s−1 was demonstrated. Furthermore, this article provides optical images of X-ray-induced explosions together with Bragg diffraction from protein microcrystals exposed to trains of X-ray pulses repeating at rates of up to 4.5 MHz. The results indicate the feasibility for megahertz serial crystallography measurements with hard X-rays and give guidance for the design of such experiments.

Wavefront sensing at X‐ray free‐electron lasers is important for quantitatively understanding the fundamental properties of the laser, for aligning X‐ray instruments and for conducting scientific experimental analysis. A fractional Talbot wavefront sensor has been developed. This wavefront sensor enables measurements over a wide range of energies, as is common on X‐ray instruments, with simplified mechanical requirements and is compatible with the high average power pulses expected in upcoming X‐ray free‐electron laser upgrades. Single‐shot measurements were performed at 500 eV, 1000 eV and 1500 eV at the Linac Coherent Light Source. These measurements were applied to study both mirror alignment and the effects of undulator tapering schemes on source properties. The beamline focal plane position was tracked to an uncertainty of 0.12 mm, and the source location for various undulator tapering schemes to an uncertainty of 1 m, demonstrating excellent sensitivity. These findings pave the way to use the fractional Talbot wavefront sensor as a routine, robust and sensitive tool at X‐ray free‐electron lasers as well as other high‐brightness X‐ray sources. [ABSTRACT FROM AUTHOR]

In this work, we analyze the application of X-ray diffraction imaging techniques to follow ultrafast structural transitions in solid materials using the example of an X-ray pump–X-ray probe experiment with a single-crystal silicon performed at a Linac Coherent Light Source. Due to the spatially non-uniform profile of the X-ray beam, the diffractive signal recorded in this experiment included contributions from crystal parts experiencing different fluences from the peak fluence down to zero. With our theoretical model, we could identify specific processes contributing to the silicon melting in those crystal regions, i.e., the non-thermal and thermal melting whose occurrences depended on the locally absorbed X-ray doses. We then constructed the total volume-integrated signal by summing up the coherent signal contributions (amplitudes) from the various crystal regions and found that this significantly differed from the signals obtained for a few selected uniform fluence values, including the peak fluence. This shows that the diffraction imaging signal obtained for a structurally damaged material after an impact of a non-uniform X-ray pump pulse cannot be always interpreted as the material’s response to a pulse of a specific (e.g., peak) fluence as it is sometimes believed. This observation has to be taken into account in planning and interpreting future experiments investigating structural changes in materials with X-ray diffraction imaging.

A compact hard X‐ray split‐and‐delay line for studying ultrafast dynamics at free‐electron laser sources is presented. The device is capable of splitting a single X‐ray pulse into two fractions to introduce time delays from −5 to 815 ps with femtosecond resolution. The split‐and‐delay line can operate in a wide and continuous energy range between 7 and 16 keV. Compact dimensions of 60 × 60 × 30 cm with a total weight of about 60 kg make it portable and suitable for direct installation in an experimental hutch. The concept of the device is based on crystal diffraction. The piezo‐driven stages utilized in the device give nanometre positioning accuracy. On‐line monitoring systems based on X‐ray cameras and intensity monitors are implemented to provide active alignment feedback. Performance estimates of the system are also presented. [ABSTRACT FROM AUTHOR]

Protein crystallography using synchrotron radiation sources has had a tremendous impact on biology, having yielded the structures of thousands of proteins and given detailed insight into their mechanisms. However, the technique is limited by the requirement for macroscopic crystals, which can be difficult to obtain, as well as by the often severe radiation damage caused in diffraction experiments, in particular when using tiny crystals. To slow radiation damage, data collection is typically performed at cryogenic temperatures. With the advent of free-electron lasers (FELs) capable of delivering extremely intense femtosecond X-ray pulses, this situation appears to be remedied, allowing the structure determination of undamaged macromolecules using either macroscopic or microscopic crystals. The latter are exposed to the FEL beam in random orientations and their diffraction data are collected at cryogenic or room temperature in a serial fashion, since each crystal is destroyed upon a single exposure. The new approaches required for crystal growth and delivery, and for diffraction data analysis, including de novo phasing, are reviewed. The opportunities and challenges of SFX are described, including applications such as time-resolved measurements and the analysis of radiation damage-prone systems.

Structural studies in general, and crystallography in particular, have benefited and still do benefit dramatically from the use of synchrotron radiation. Low-emittance storage rings of the third generation provide focused beams down to the micrometre range that are sufficiently intense for the investigation of weakly scattering crystals down to the size of several micrometres. Even though the coherent fraction of these sources is below 1%, a number of new imaging techniques have been developed to exploit the partially coherent radiation. However, many techniques in nanoscience are limited by this rather small coherent fraction. On the one hand, this restriction limits the ability to study the structure and dynamics of non-crystalline materials by methods that depend on the coherence properties of the beam, like coherent diffractive imaging and X-ray correlation spectroscopy. On the other hand, the flux in an ultra-small diffraction-limited focus is limited as well for the same reason. Meanwhile, new storage rings with more advanced lattice designs are under construction or under consideration, which will have significantly smaller emittances. These sources are targeted towards the diffraction limit in the X-ray regime and will provide roughly one to two orders of magnitude higher spectral brightness and coherence. They will be especially suited to experiments exploiting the coherence properties of the beams and to ultra-small focal spot sizes in the regime of several nanometres. Although the length of individual X-ray pulses at a storage-ring source is of the order of 100 ps, which is sufficiently short to track structural changes of larger groups, faster processes as they occur during vision or photosynthesis, for example, are not accessible in all details under these conditions. Linear accelerator (linac) driven free-electron laser (FEL) sources with extremely short and intense pulses of very high coherence circumvent some of the limitations of present-day storage-ring sources. It has been demonstrated that their individual pulses are short enough to outrun radiation damage for single-pulse exposures. These ultra-short pulses also enable time-resolved studies 1000 times faster than at standard storage-ring sources. Developments are ongoing at various places for a totally new type of X-ray source combining a linac with a storage ring. These energy-recovery linacs promise to provide pulses almost as short as a FEL, with brilliances and multi-user capabilities comparable with a diffraction-limited storage ring. Altogether, these new X-ray source developments will provide smaller and more intense X-ray beams with a considerably higher coherent fraction, enabling a broad spectrum of new techniques for studying the structure of crystalline and non-crystalline states of matter at atomic length scales. In addition, the short X-ray pulses of FELs will enable the study of fast atomic dynamics and non-equilibrium states of matter.

The durability of grazing- and normal-incidence optical coatings has been experimentally assessed under free-electron laser irradiation at various numbers of pulses up to 16 million shots and various fluence levels below 10% of the single-shot damage threshold. The experiment was performed at FLASH, the Free-electron LASer in Hamburg, using 13.5 nm extreme UV (EUV) radiation with 100 fs pulse duration. Polycrystalline ruthenium and amorphous carbon 50 nm thin films on silicon substrates were tested at total external reflection angles of 20° and 10° grazing incidence, respectively. Mo/Si periodical multilayer structures were tested in the Bragg reflection condition at 16° off-normal angle of incidence. The exposed areas were analysed post-mortem using differential contrast visible light microscopy, EUV reflectivity mapping and scanning X-ray photoelectron spectroscopy. The analysis revealed that Ru and Mo/Si coatings exposed to the highest dose and fluence level show a few per cent drop in their EUV reflectivity, which is explained by EUV-induced oxidation of the surface. [ABSTRACT FROM AUTHOR]

The data systems for X-ray free-electron laser (FEL) experiments at the Linac coherent light source (LCLS) are described. These systems are designed to acquire and to reliably transport shot-by-shot data at a peak throughput of 5 GB/s to the offline data storage where experimental data and the relevant metadata are archived and made available for user analysis. The analysis and monitoring implementation (AMI) and Photon Science ANAlysis (psana) software packages are described. Psana is open source and freely available. [ABSTRACT FROM AUTHOR]

The data acquisition and data management systems for X-ray free-electron laser experiments at the Linac Coherent Light Source are described. These systems are designed to acquire and to reliably transport shot-by-shot data at a peak throughput of 5 GB s−1 to the offline data storage, where experimental data and the relevant metadata are archived and made available for user analysis. A case study of a serial femtosecond crystallography pipeline is presented. [ABSTRACT FROM AUTHOR]

CASS [Foucar et al. (2012). Comput. Phys. Commun. 183, 2207-2213] is a well established software suite for experiments performed at any sort of light source. It is based on a modular design and can easily be adapted for use at free-electron laser (FEL) experiments that have a biological focus. This article will list all the additional functionality and enhancements of CASS for use with FEL experiments that have been introduced since the first publication. The article will also highlight some advanced experiments with biological aspects that have been performed. [ABSTRACT FROM AUTHOR]

Klassifikationen aufgrund von Indexwerten wie Q oder RMR, die sich aus der Multiplikation oder Addition verschiedener physikalischer Parameter oder gar Bewertungen ergeben, dürfen weder zur Beurteilung des Gebirgsverhaltens beim Vortrieb noch zur Festlegung der Ausbruchsicherung herangezogen werden. Ein Klassifikationssystem sollte nur jene Merkmale und Eigenschaften zum Gegenstand haben, die für die Beantwortung konkreter Fragestellungen der Planung signifikant sind. Die genannten Indexwerte erfüllen diese Bedingung nicht. Wissenschaftlich unhaltbar sind auch die verschiedentlich vorgeschlagenen Beziehungen zwischen dem so genannten GSI-Wert und dem Gebirgs-E-Modul oder den Festigkeitsparametern der so genannten empirischen Hoek-Brownschen Bruchbedingung. Letztere ist weder genauer, noch einfacher als die in der Geotechnik etablierte Mohr-Coulombsche Bruchbedingung. Die empirische Basis der postulierten Beziehungen zwischen den Gebirgsparametern und dem GSI wurde nie veröffentlicht. Eine kritische Überprüfung dieser Beziehungen ist daher nicht möglich. On the rock mass classifications with indices in tunnelling. Classifications based on indices such as Q or RMR, which result from the multiplication or addition of various physical parameters or ratings, should not be used to estimate the rock mass behaviour or the necessary tunnel support. A classification system should take account only of the characteristics and properties that are significant when addressing specific planning issues. The mentioned indices do not fulfil this condition. The proposed relationships between the so-called Geological Strength Index (GSI) and the rock mass parameters under the empirical Hoek-Brown failure condition are also scientifically untenable. This failure condition is neither more accurate nor easier to handle than the familiar linear Mohr-Coulomb condition. The proposed relationships defy scientific testing because their empirical basis has never been published and, in addition, they contain non-measurable entities. [ABSTRACT FROM AUTHOR]

Abstract: Several new light source projects aim at producing X-ray photons with high repetition rate (1kHz or above). Cost and size considerations have recently stirred new interest in solutions based on X-band RF systems. We developed a conceptual design for a soft X-ray FEL driven by X-band structures operating at high repetition rate and we present here the results of the start-to-end simulations from the gun to the end of the undulators and the corresponding optimisation of the FEL performance at 1keV photon energy. [Copyright &y& Elsevier]

In the next decade the scientific community expects a strong impact in physics, chemistry, biology, material research and life sciences by the availability of high-brilliance X-ray radiation from free-electron laser (FEL) sources. In particular, in the field of ultrafast science these new sources will allow new types of experiments, enabling new phenomena to be discovered. Whereas today ultrafast X-ray diffraction experiments are strongly restricted by the limited X-ray flux of current sources of sub-picosecond X-ray pulses, FELs will provide short pulses of typically 1012 photons with a duration of the order of 100 fs and monochromaticity of 10−3. Here, the feasibility of time-resolved single-shot powder diffraction experiments using these intense pulses, and the requirements of these experiments, are discussed. The detector count rates are estimated for diffraction from a model compound in a wide q-regime under the special consideration of high resolving power. In the case of LCLS radiation parameters, single-shot experiments will be feasible although high-resolution powder diffraction will require a reduction of the intrinsic FEL radiation bandwidth. [ABSTRACT FROM AUTHOR]

Peking University Superconducting Accelerator Facility (PKU-SCAF) is to generate high-quality electron beams with high average current. It is mainly composed of a DC-SC photocathode injector and a superconducting accelerator. It will operate in CW mode. The energy of the electrons is 20–35 MeV and the emittance is <15 π mm mrad. PKU-SCAF will be used for Free Electron Lasers. [Copyright &y& Elsevier]