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Large-bandwidth pulses produced by cutting-edge X-ray free-electron lasers (FELs) are of great importance in research fields like material science and biology. In this paper, a new method to generate high-power ultrashort FEL pulses with tunable spectral bandwidth with spectral coherence using a dielectric-lined waveguide without interfering operation of linacs is proposed. By exploiting the passive and dephasingless wakefield at terahertz frequency excited by the beam, stable energy modulation can be achieved in the electron beam and large-bandwidth high-intensity soft X-ray radiation can be generated. Three-dimensional start-to-end simulations have been carried out and the results show that coherent radiation pulses with duration of a few femtoseconds and bandwidths ranging from 1.01% to 2.16% can be achieved by changing the undulator taper profile. [ABSTRACT FROM AUTHOR]

The Earth's magnetosheath and cusps are the sources of soft X‐rays. In the accompanying paper (Part 1) and this paper, we discuss the methods of finding the magnetopause position by analyzing the X‐ray images. We use the software developed for the Soft X‐ray Imager (SXI) on board the forthcoming Solar wind Magnetosphere Ionosphere Link Explorer (SMILE) mission. We show how to find the maximum SXI count rate in noisy count maps. We verify the assumption that the maximum of the X‐ray emissivity integrated along the Line‐of‐Sight (Ix) is tangent to the magnetopause. We consider two cases using two MHD models and apply different methods of magnetospheric masking. Overall, the magnetopause is located close to the maximum Ix gradient or between the maximum Ix gradient and the maximum Ix depending on the method used. But since the angular distance between the maximum Ix gradient and the maximum Ix is relatively small (about 3°), the maximum Ix might be used as an indicator of the outer boundary of a wide magnetopause layer usually obtained in MHD simulations. Plain Language Summary: This is the second of two papers presenting the techniques to estimate the Earth's magnetopause location (the outer boundary of the magnetosphere) under the impact of the highly dynamic solar wind. Our knowledge of the overall shape of the magnetopause will be vastly improved when we start using X‐ray imagers to monitor large areas around this boundary as the solar wind varies. In this second paper of the series, we make use of the X‐ray emissions in the vicinity of the Earth simulated in the first paper for two case studies with vastly different incoming solar wind conditions. Here we examine different methods of how to extract the magnetopause shape and position from X‐ray maps of the type that will be returned by the X‐ray imager due to flying on the SMILE mission. Key Points: Different methods of finding the location and shape of the magnetopause from X‐ray images give consistent resultsMaximum integrated emissivity indicates the outer boundary of the magnetopauseThis work is made in preparation for the forthcoming Solar wind Magnetosphere Ionosphere Link Explorer mission [ABSTRACT FROM AUTHOR]

The Shanghai Soft X-ray Free-Electron Laser (SXFEL) is the first X-ray freeelectron laser facility in China. The SASE beamline, which consists of a pinkbeam branch and a mono-beam branch, is one of the two beamlines in the Phase-I construction. The pink-beam branch opened for users in 2023 after successful first-round beamline commissioning. In this paper, the design of the beamline is presented and the performance of the pink-beam branch is reported. The measured energy-resolving power of the online spectrometer is over 6000 @ 400 eV. The focusing spot size of the pink beam is less than 3 μm in both the horizontal and vertical at the endstation. [ABSTRACT FROM AUTHOR]

With fast advances in enhancing the focusing/imaging resolution of Fresnel zone plate lenses toward sub-10 nm, low diffraction efficiency in connection with their rectangular zone shape still remains a big issue in both soft and hard X-ray microscopy. In hard X-ray optics, encouraging progress has recently been reported in our earlier attempts of high focusing efficiency by 3D kinoform shaped metallic zone plates, formed by greyscale electron beam lithography. This paper addresses our efforts towards high focusing/imaging efficiency by developing a novel dielectric kinoform zone plate lens for soft X-rays. The effects of the zone materials and zone shapes on the focusing/imaging quality were first theoretically investigated by a modified thin-grating-approximation method, revealing superior efficiencies of dielectric kinoform zone plates over rectangular ones in metals. Optical characterizations of replicated dielectric kinoform zone plates by greyscale electron beam lithography demonstrate a focusing efficiency of 15.5% with a resolution of 110 nm in the water window of X-rays. Apart from high efficiency, the novel kinoform zone plate lenses developed in this work exhibit significant advantages over conventional zone plates, i.e. simplified process, low cost and no need for a beamstop. [ABSTRACT FROM AUTHOR]

MAX IV is a fourth‐generation, or diffraction‐limited, synchrotron light source with a number of state‐of‐the‐art beamlines. The performance of a beamline is, to a high degree, set by the energy resolution it can achieve, which in turn is governed to a large extent by the monochromator. During the design phase of a monochromator, the mechanical requirements must be fully understood and met with margin. During commissioning, the performance must be verified and optimized. In this paper, six soft X‐ray monochromators at MAX IV beamlines (Bloch, Veritas, HIPPIE, SPECIES, FinEstBeAMS and SoftiMAX) are examined with a focus on their resolving power, energy range and the time required to change measurement range, as those parameters are dependent on each other. The monochromators have a modern commercial design, planned and developed in close collaboration with the vendors. This paper aims to present the current status of the commissioning at MAX IV with emphasis on elucidating the mechanical limitations on the performance of the monochromators. It contains analysis of the outcome and our approach to achieve fast and high‐resolution monochromators. [ABSTRACT FROM AUTHOR]

The magnetopause standoff distance characterizes global magnetospheric compression and deformation in response to changes in the solar wind dynamic pressure and interplanetary magnetic field orientation. We cannot derive this parameter from in situ spacecraft measurements. However, time series of the magnetopause standoff distance can be obtained in the near future using observations by soft X‐ray imagers. In two companion papers, we describe methods of finding the standoff distance from X‐ray images. In Part 1, we present the results of MHD simulations which we use for the calculation of the X‐ray emissivity in the magnetosheath and cusps. Some MHD models predict relatively high density in the magnetosphere, larger than observed in the data. Correcting this, we develop magnetospheric masking methods to separate the magnetosphere from the magnetosheath and cusps. We simulate the X‐ray emissivity in the magnetosheath for different solar wind conditions and dipole tilts. Plain Language Summary: The highly dynamic solar wind continuously bombards the Earth's magnetosphere, which changes shape in response. The magnetopause is the outer boundary of the magnetosphere, which is known to move. We are limited in our knowledge of the overall shape of the magnetopause, as current in situ measurements can only tell us about any change in the magnetopause at one specific location. Spacecraft carrying soft X‐ray imagers, however, will soon revolutionize our understanding by monitoring large areas of the magnetopause as the solar wind varies. In this first of a series of two papers, we simulate X‐ray emissions in the vicinity of the Earth using two magnetohydrodynamic models, and for two case studies with vastly different incoming solar wind conditions. In a subsequent paper, we examine methods how to extract the magnetopause shape from the simulated X‐ray images. Key Points: The SMILE mission will carry soft X‐ray imager onboardMagnetospheric masking methods separate the magnetosphere from the magnetosheath and cuspsWe make magnetospheric masks using threshold conditions and flowlines [ABSTRACT FROM AUTHOR]

This article presents a demonstration of the improved performance of an X‐ray free‐electron laser (FEL) using the optical klystron mechanism and helical undulator configuration, in comparison with the common planar undulator configuration without optical klystron. The demonstration was carried out at Athos, the soft X‐ray beamline of SwissFEL. Athos has variable‐polarization undulators, and small magnetic chicanes placed between every two undulators to fully exploit the optical klystron. It was found that, for wavelengths of 1.24 nm and 3.10 nm, the required length to achieve FEL saturation is reduced by about 35% when using both the optical klystron and helical undulators, with each effect accounting for about half of the improvement. Moreover, it is shown that a helical undulator configuration provides a 20% to 50% higher pulse energy than planar undulators. This work represents an important step towards more compact and high‐power FELs, rendering this key technology more efficient, affordable and accessible to the scientific community. [ABSTRACT FROM AUTHOR]

In this paper the design of the free‐electron laser (FEL) in the SXL (Soft X‐ray Laser) project at the MAX IV Laboratory is presented. The target performance parameters originate in a science case put forward by Swedish users and the SXL FEL is foreseen to be driven by the existing MAX IV 3 GeV linac. The SXL project is planned to be realized in different stages and in this paper the focus is on Phase 1, where the basic operation mode for the FEL will be SASE (self‐amplified spontaneous emission), with an emphasis on short pulses. Simulation results for two linac bunches (high and low charge) with different pulse duration are illustrated, as well as the performance for two‐color/two‐pulses mode and power enhancement through tapering. Besides standard SASE and optical klystron configurations, the FEL setup is also tailored to allow for advanced seeding schemes operations. Finally possible upgrades that will be implemented in a second phase of the project are discussed. [ABSTRACT FROM AUTHOR]

Soft X‐ray tomography (SXT) is an imaging technique to visualise whole cells without fixation, staining, and sectioning. For SXT imaging, cells are cryopreserved and imaged at cryogenic conditions. Such 'near‐to‐native' state imaging is in high demand and initiated the development of the laboratory table‐top SXT microscope. As many laboratories do not have access to cryogenic equipment, we asked ourselves whether SXT imaging is feasible on dry specimens. This paper shows how the dehydration of cells can be used as an alternative sample preparation to obtain ultrastructure information. We compare different dehydration processes on mouse embryonic fibroblasts in terms of ultrastructural preservation and shrinkage. Based on this analysis, we chose critical point (CPD) dried cells for SXT imaging. In comparison to cryopreserved and air‐dried cells, CPD dehydrated cells show high structural integrity although with about 3–7 times higher X‐ray absorption for cellular organelles. As the difference in X‐ray absorption values between organelles is preserved, 3D anatomy of CPD‐dried cells can be segmented and analysed, demonstrating the applicability of CPD‐dried sample preparation for SXT imaging. LAY DESCRIPTION: Soft X‐ray tomography (SXT) is an imaging technique that allows to see the internal structures of cells without the need for special treatments like fixation or staining. Typically, SXT imaging involves freezing and imaging cells at very low temperatures. However, since many labs lack the necessary equipment, we explored whether SXT imaging could be done on dry samples instead. We compared different dehydration methods and found that critical point drying (CPD) was the most promising for SXT imaging. CPD‐dried cells showed high structural integrity, although they absorbed more X‐rays than hydrated cells, demonstrating that CPD‐dried sample preparation is a viable alternative for SXT imaging. [ABSTRACT FROM AUTHOR]

FlexPES is a soft X-ray beamline on the 1.5 GeV storage ring at MAX IV Laboratory, Sweden, providing horizontally polarized radiation in the 40-1500 eV photon energy range and specializing in high-resolution photoelectron spectroscopy, fast X-ray absorption spectroscopy and electron-ion/ion-ion coincidence techniques. The beamline is split into two branches currently serving three endstations, with a possibility of adding a fourth station at a free port. The refocusing optics provides two focal points on each branch, and enables either focused or defocused beam on the sample. The endstation EA01 at branch A (Surface and Materials Science) is dedicated to surface- and materials-science experiments on solid samples at ultra-high vacuum. It is well suited not only to all flavours of photoelectron spectroscopy but also to fast (down to sub-minute) high-resolution X-ray absorption measurements with various detectors. Branch B (Low-Density Matter Science) has the possibility to study gas-phase/liquid samples at elevated pressures. The first endstation of this branch, EB01, is a mobile setup for various ion-ion and electron-ion coincidence techniques. It houses a versatile reaction microscope, which can be used for experiments during single-bunch or multi-bunch delivery. The second endstation, EB02, is based on a rotatable chamber with an electron spectrometer for photoelectron spectroscopy studies on primarily volatile targets, and a number of peripheral setups for sample delivery, such as molecular/cluster beams, metal/semiconductor nanoparticle beams and liquid jets. This station can also be used for non-UHV photoemission studies on solid samples. In this paper, the optical layout and the present performance of the beamline and all its endstations are reported. [ABSTRACT FROM AUTHOR]

Synchrotron light sources can provide the required spatial coherence, stability and control to support the development of advanced lithography at the extreme ultraviolet and soft X-ray wavelengths that are relevant to current and future fabricating technologies. Here an evaluation of the optical performance of the soft X-ray (SXR) beamline of the Australian Synchrotron (AS) and its suitability for developing interference lithography using radiation in the 91.8 eV (13.5 nm) to 300 eV (4.13 nm) range are presented. A comprehensive physical optics model of the APPLE-II undulator source and SXR beamline was constructed to simulate the properties of the illumination at the proposed location of a photomask, as a function of photon energy, collimation and monochromator parameters. The model is validated using a combination of experimental measurements of the photon intensity distribution of the undulator harmonics. It is shown that the undulator harmonics intensity ratio can be accurately measured using an imaging detector and controlled using beamline optics. Finally, the photomask geometric constraints and achievable performance for the limiting case of fully spatially coherent illumination are evaluated. [ABSTRACT FROM AUTHOR]

Calculations and measurements of polarization-dependent soft X-ray scattering intensity are presented during a magnetic hysteresis cycle. It is confirmed that the dependence of the intensity on the magnetic moment can be linear, quadratic or a combination of both, depending on the polarization of the incident X-ray beam and the direction of the magnetic moment. With a linearly polarized beam, the scattered intensity will have a purely quadratic dependence on the magnetic moment when the magnetic moment is parallel to the scattering plane. However, with the magnetic moment perpendicular to the scattering plane, there is also a linear component. This means that, when measuring the hysteresis with linear polarization during a hysteresis cycle, the intensity will be an even function of the applied field when the change in the magnetic moment (and field) is confined within the scattering plane but becomes more complicated when the magnetic moment is out of the scattering plane. Furthermore, with circular polarization, the dependence of the scattered intensity on the moment is a combination of linear and quadratic. With the moment parallel to the scattering plane, the linear component changes with the helicity of the incident beam. Surprisingly, in stark contrast to absorption studies, even when the magnetic moment is perpendicular to the scattering plane there is still a dependence on the moment with a linear component. This linear component is completely independent of the helicity of the beam, meaning that the hysteresis loops will not be inverted with helicity. [ABSTRACT FROM AUTHOR]

Memristive devices are under intense development as non‐volatile memory elements for extending the computing capabilities of traditional silicon technology by enabling novel computing primitives. In this respect, interface‐based memristive devices are promising candidates to emulate synaptic functionalities in neuromorphic circuits aiming to replicate the information processing of nervous systems. A device composed of Nb/NbOx/Al2O3/HfO2/Au that shows promising features like analog switching, no electro‐forming, and high current‐voltage non‐linearity is reported. Synchrotron‐based X‐ray photoelectron spectroscopy and depth‐dependent hard X‐ray photoelectron spectroscopy are used to probe in situ different resistance states and thus the origin of memristive switching. Spectroscopic evidence for memristive switching based on the charge state of electron traps within HfO2 is found. Electron energy loss spectroscopy and transmission electron microscopy support the analysis. A device model is proposed that considers a two‐terminal metal–insulator–semiconductor structure in which traps within the insulator (HfO2/Al2O3) modulate the space charge region within the semiconductor (NbOx) and, thereby, the overall resistance. The experimental findings are in line with impedance spectroscopy data reported in the companion paper (Marquardt et al). Both works complement one another to derive a detailed device model, which helps to engineer device performance and integrate devices into silicon technology. [ABSTRACT FROM AUTHOR]

This paper mainly discusses the applicability of using soft x‐ray tomography technology to examine the multidimensional structure of metal–organic frameworks, such as their core‐shell and hollow framework, by visually observing their corresponding images in different energy bands by different excitation energies for different elements. The results show that the use of soft x‐ray tomography (SXT) can effectively observe the distribution of metals in the structure, as well as observe the type of hollow pores the metal–organic framework (MOF) possesses. This pioneering evaluation of MOFs via SXT shows excellent performance in the structure identification of multidimensional metal–organic frameworks. [ABSTRACT FROM AUTHOR]

A numerical study of the effect of betatron oscillations on the second harmonic generation in free‐electron lasers (FELs) is presented. Analytical expressions for the effective coupling strength factors are derived that clearly distinguish all contributions in subharmonics and each polarization of the radiation. A three‐dimensional time‐dependent numerical FEL code that takes into account the main FEL effects and the individual contribution of each electron to the second harmonic generation is presented. Also, the X‐ and Y‐polarizations of the second harmonic are analyzed. The second harmonic was detected in experiments at the Advanced Photon Source (APS) Low Energy Undulator Test Line (LEUTL) and Linac Coherent Light Source (LCLS) in the soft X‐ray regime. The approach presented in the article can be useful for a comprehensive study and diagnostics of XFELs. In the paper, the LCLS and Pohang Accelerator Laboratory X‐ray Free‐Electron Laser (PAL‐XFEL) experiments are modeled. The simulation results are in a good agreement with the experimental data. [ABSTRACT FROM AUTHOR]

X‐ray absorption is a sensitive and versatile tool for chemical speciation. However, when high doses are used, the absorbed energy can change the composition, amount and structure of the native material, thereby changing the aspects of the absorption process on which speciation is based. How can one calculate the dose when X‐ray irradiation affects the chemistry and changes the amount of the material? This paper presents an assumption‐free approach which can retrieve from the experimental data all dose‐sensitive parameters – absorption coefficients, composition (elemental molecular units), material densities – which can then be used to calculate accurate doses as a function of irradiation. This approach is illustrated using X‐ray damage to a solid film of a perfluorosulfonic acid fluoropolymer in a scanning transmission soft X‐ray microscope. This new approach is compared against existing dose models which calculate the dose by making simplifying assumptions regarding the material quantity, density and chemistry. While the detailed measurements used in this approach go beyond typical methods to experimental analytical X‐ray absorption, they provide a more accurate quantitation of radiation dose, and help to understand mechanisms of radiation damage. [ABSTRACT FROM AUTHOR]

This work investigates the performance of the electrospray aerosol generator at the European X-ray Free Electron Laser (EuXFEL). This generator is, together with an aerodynamic lens stack that transports the particles into the X-ray interaction vacuum chamber, the method of choice to deliver particles for single-particle coherent diffractive imaging (SPI) experiments at the EuXFEL. For these experiments to be successful, it is necessary to achieve high transmission of particles from solution into the vacuum interaction region. Particle transmission is highly dependent on efficient neutralization of the charged aerosol generated by the electrospray mechanism as well as the geometry in the vicinity of the Taylor cone. We report absolute particle transmission values for different neutralizers and geometries while keeping the conditions suitable for SPI experiments. Our findings reveal that a vacuum ultraviolet ionizer demonstrates a transmission efficiency approximately seven times greater than the soft X-ray ionizer used previously. Combined with an optimized orifice size on the counter electrode, we achieve >40% particle transmission from solution into the X-ray interaction region. These findings offer valuable insights for optimizing electrospray aerosol generator configurations and data rates for SPI experiments. [ABSTRACT FROM AUTHOR]

The SPECIES beamline has been transferred to the new 1.5 GeV storage ring at the MAX IV Laboratory. Several improvements have been made to the beamline and its endstations during the transfer. Together the Ambient Pressure X‐ray Photoelectron Spectroscopy and Resonant Inelastic X‐ray Scattering endstations are capable of conducting photoelectron spectroscopy in elevated pressure regimes with enhanced time‐resolution and flux and X‐ray scattering experiments with improved resolution and flux. Both endstations offer a unique capability for experiments at low photon energies in the vacuum ultraviolet and soft X‐ray range. In this paper, the upgrades on the endstations and current performance of the beamline are reported. [ABSTRACT FROM AUTHOR]

In this paper the back‐side‐illuminated Percival 2‐Megapixel (P2M) detector is presented, along with its characterization by means of optical and X‐ray photons. For the first time, the response of the system to soft X‐rays (250 eV to 1 keV) is presented. The main performance parameters of the first detector are measured, assessing the capabilities in terms of noise, dynamic range and single‐photon discrimination capability. Present limitations and coming improvements are discussed. [ABSTRACT FROM AUTHOR]

The impressive progress in the performance of synchrotron radiation sources is nowadays driven by the so‐called 'ultimate storage ring' projects which promise an unprecedented improvement in brightness. Progress on the detector side has not always been at the same pace, especially as far as soft X‐ray 2D detectors are concerned. While the most commonly used detectors are still based on microchannel plates or CCD technology, recent developments of CMOS (complementary metal oxide semiconductor)‐type detectors will play an ever more important role as 2D detectors in the soft X‐ray range. This paper describes the capabilities and performance of a camera equipped with a newly commercialized backside‐illuminated scientific CMOS (sCMOS‐BSI) sensor, integrated in a vacuum environment, for soft X‐ray experiments at synchrotron sources. The 4 Mpixel sensor reaches a frame rate of up to 48 frames s−1 while matching the requirements for X‐ray experiments in terms of high‐intensity linearity (>98%), good spatial homogeneity (<1%), high charge capacity (up to 80 ke−), and low readout noise (down to 2 e− r.m.s.) and dark current (3 e− per second per pixel). Performance evaluations in the soft X‐ray range have been carried out at the METROLOGIE beamline of the SOLEIL synchrotron. The quantum efficiency, spatial resolution (24 line‐pairs mm−1), energy resolution (<100 eV) and radiation damage versus the X‐ray dose (<600 Gy) have been measured in the energy range from 40 to 2000 eV. In order to illustrate the capabilities of this new sCMOS‐BSI sensor, several experiments have been performed at the SEXTANTS and HERMES soft X‐ray beamlines of the SOLEIL synchrotron: acquisition of a coherent diffraction pattern from a pinhole at 186 eV, a scattering experiment from a nanostructured Co/Cu multilayer at 767 eV and ptychographic imaging in transmission at 706 eV. [ABSTRACT FROM AUTHOR]

This paper presents a novel cantilevered liquid‐nitrogen‐cooled silicon mirror design for the first optic in a new soft X‐ray beamline that is being developed as part of the Advanced Light Source Upgrade (ALS‐U) (Lawrence Berkeley National Laboratory, USA). The beamline is optimized for photon energies between 400 and 1400 eV with full polarization control. Calculations indicate that, without correction, this design will achieve a Strehl ratio greater than 0.85 for the entire energy and polarization ranges of the beamline. With a correction achieved by moving the focus 7.5 mm upstream, the minimum Strehl ratio is 0.99. This design is currently the baseline plan for all new ALS‐U insertion device beamlines. [ABSTRACT FROM AUTHOR]

Charge exchange (CX) is a semi‐resonant recombination process that can lead to spectral line emission in the X‐ray band. It occurs in nearly any environment where hot plasma and cold gas interact: in the solar system, in comets and planetary atmospheres, and likely astrophysically, in, for example, supernova remnants and galaxy clusters. It also contributes to the soft X‐ray background. Accurate spectral modeling of CX is thus critical to properly interpreting our astrophysical observations, but the commonly used CX models in popular spectral fitting packages often rely on scaling equations and may not accurately describe observations or laboratory measurements. This paper introduces a method that can be applied to high‐resolution CX spectra to directly extract state‐selective CX cross‐sections for electron capture, a key parameter for properly simulating the resulting CX spectrum. [ABSTRACT FROM AUTHOR]

The Earth's magnetosheath and cusps emit soft X‐rays due to the charge exchange between highly charged solar wind ions and exospheric hydrogen atoms. The Lunar Environment Heliospheric X‐ray Imager and Solar wind Magnetosphere Ionosphere Link Explorer missions are scheduled to image the Earth's dayside magnetosphere system in soft X‐rays to investigate global‐scale magnetopause reconnection modes under varying solar wind conditions. The exospheric neutral hydrogen density distribution, especially the value of this density at the subsolar magnetopause is of particular interest for understanding X‐ray emissions near this boundary. This paper estimates the exospheric density during solar minimum using the X‐ray Multimirror Mission (XMM) astrophysics observatory. We selected an event on 12 November 2008 from the XMM data archive, which detects soft X‐rays of magnetosheath origin while solar wind and interplanetary magnetic field conditions are relatively constant. During the event the location of the magnetopause was measured in situ by the THEMIS mission, thus the location of the solar wind ions responsible for the magnetosheath emission is well constrained by observation. We estimated the exospheric density using the Open Geospace Global Circulation Model (OpenGGCM) and a spherically symmetric exosphere model. The ratio of the magnetosheath plasma flux between the OpenGGCM model and the THEMIS, was nearly 1, which means the magnetohydrodynamic model reasonably reproduces the magnetosheath plasma conditions. The OpenGGCM magnetosheath parameters were used to deconvolve soft X‐rays of exospheric origin from the XMM signal. The lower‐limit of the exospheric density of this solar minimum event is 36.8 ± 11.7 cm−3 at 10 RE subsolar location. Key Points: From 11 years of X‐ray Multimirror Mission‐Newton X‐ray observations, we identified 193 intervals that can be used to estimate the exospheric neutral densityWe derived a solar minimum exospheric neutral density from the 12 November 2008 event using a global MagnetoHydroDynamics model and a simplified exosphere modelThe density estimate is 36.8 cm−3 near the subsolar magnetopause and is likely a lower‐limit value [ABSTRACT FROM AUTHOR]

Comprehensive Summary: Hydrogen‐bonded organic networks (HONs) have attracted intense research interest due to their mild synthesis conditions, good solvent processability and strong reproducibility. Most HONs are constructed by electrically neutral organic ligands through intermolecular interactions such as weak hydrogen bonding, π‐π stacking. But there are a few charge‐assisted hydrogen‐bonding networks (CAHONs) constructed by oppositely charged organic components. Under hydrothermal conditions, we successfully synthesized a 3D CAHON (H2CV)(H2BTEC) (1) constructed by H2CV (CV = N,N′‐4,4′‐bipyridine dipropionate) and H4BTEC (H4BTEC = 1,2,4,5‐benzenetetracarboxylic acid) through multiple charge‐assisted hydrogen bonding. Upon soft X‐ray, ultraviolet light or sunlight irradiation under ambient conditions, 1 quickly changes from colorless to blue (1P), and kinetic calculations show that its photochromism meets first‐order dynamics. Interestingly, the colored crystals 1P with long‐lived colored radicals will not fade after being placed for more than two months at room temperature in air, owing to the fact that the photogenerated viologen radicals can be stabilized by the abundant hydrogen bonds, the coplanar pyridinium rings and the slow electron‐hole recombination. Moreover, 1 is a typical direct band gap semiconductor, evidenced by the calculated band gap of 3.24 eV, in agreement with the experimental value of 3.40 eV. In view of its strong colored stability, 1 is designed for distinctive inkless printing. [ABSTRACT FROM AUTHOR]

We present a method to explore the effect of fluorescence on X‐ray attenuation measurements obtained from X‐ray absorption spectroscopy (XAS). We use the X‐ray extended range technique‐like method (XERT‐like). The experimental setup includes different sized apertures to control the number of secondary X‐rays entering the detector. Comparison of attenuation measurements produced with different aperture combination permit investigation of the effect of fluorescence radiation. In this work, fluorescence has a large impact on the attenuation measurements of thick zinc foils. The correction is energy‐dependent and sample thickness‐dependent and changes the structure and relative amplitudes of oscillations in the near‐edge region. Correction for this systematic is important for absolute measurement, for edge‐jump and edge characterization, and for near‐edge structure and amplitudes. A significant background scattering due to zinc fluorescence from the beamline optics was identified and treated for the first time. The model theory fits the experimental measurements well. The resulting correction is most significant for thicker foils with the 50 μm sample experiencing a shift in attenuation of up to 15.5% for the largest aperture while the 25 and 10 μm samples saw corrections of up to 0.153 and 0.00639% respectively. The standard error from the dispersion and variance was reduced by up to 50.5% after the correction for the 50 μm sample. This enables high‐accuracy data and theoretical and experimental analysis to below 0.03% accuracy. The technology is advanced. There is a cost in preparation and measurement time of less than a factor of two, and the principles are clear and can be routinely implemented on any beamline. This paper focuses on the model and parameters for fluorescence. [ABSTRACT FROM AUTHOR]

Based on the the third‐order aberration theory of plane‐symmetric optical systems, this paper studies the effect on aberrations of the second‐order accuracy of aperture‐ray coordinates and the extrinsic aberrations of this kind of optical system; their calculation expressions are derived. The resultant aberration expressions are then applied to calculate the aberrations of two design examples of soft X‐ray and vacuum ultraviolet (XUV) optical systems; images are compared with ray‐tracing results using SHADOW software to validate the aberration expressions. The study shows that the accuracy of the aberration expressions is satisfactory. [ABSTRACT FROM AUTHOR]

The characterization of X-ray focal spots is of great significance for the diagnosis and performance optimization of focusing systems. X-ray free-electron lasers (XFELs) are the latest generation of X-ray sources with ultrahigh brilliance, ultrashort pulse duration and nearly full transverse coherence. Because each XFEL pulse is unique and has an ultrahigh peak intensity, it is difficult to characterize its focal spot size individually with full power. Herein, a method for characterizing the spot size at the focus position is proposed based on coherent diffraction imaging. A numerical simulation was conducted to verify the feasibility of the proposed method. The focal spot size of the Coherent Scattering and Imaging endstation at the Shanghai Soft X-ray Free Electron Laser Facility was characterized using the method. The full width at half-maxima of the focal spot intensity and spot size in the horizontal and vertical directions were calculated to be 2.10 ± 0.24 mm and 2.00 ± 0.20 mm, respectively. An ablation imprint on the silicon frame was used to validate the results of the proposed method. [ABSTRACT FROM AUTHOR]

The quest for ever-shorter optical pulses has been ongoing for over half a century. Although few-cycle pulses have been generated for nearly 40 years, pulse lengths below the single-cycle limit have remained an elusive goal for a long time. For this purpose, optical waveform synthesizers, generating high-energy, high-average-power pulses via coherent combination of multiple pulses covering different spectral regions, have been recently developed. They allow unprecedented control over the generated optical waveforms, spanning an extremely broad spectral range from ultraviolet to infrared. Such control allows for steering strong-field interactions with increased degrees of freedom. When driving high-harmonic generation, tailored waveforms can produce bright attosecond pulse trains and even isolated attosecond pulses with tunable spectra up to the soft X-ray range. In this paper recent progress on parametric and hollow-core fiber waveform synthesizers is discussed. Newly developed seeding schemes; absolute, relative, and spectral phase measurement; and control techniques suitable for synthesizers are described. The progress on serial and parallel waveform synthesis based on Ti:sapphire and Ytterbium laser systems and their latest applications in high-harmonic generation in gaseous and solid media, attosecond science, and laser wakefield acceleration is discussed. [ABSTRACT FROM AUTHOR]

A phase-merging enhanced harmonic generation free-electron laser (FEL) was proposed to increase the harmonic conversion efficiency of seeded FELs and promote the radiation wavelength towards the X-ray spectral region. However, this requires a specially designed transverse gradient undulator (TGU) as the modulator to couple the transverse and longitudinal phase space of the electron beam. In this paper, the generation of the phase-merging effect is explored using the natural field gradient of a normal planar undulator. In this method, a vertical dispersion on the electron beam is introduced and then the dispersed beam travels through a normal modulator in a vertical off-axis orbit where the vertical field gradient is selected properly in terms of the vertical dispersion strength and modulation amplitude. The phase-merging effect will be generated after passing through the dispersive chicane. Theoretical analysis and numerical simulations for a seeded soft X-ray FEL based on parameters of the Shanghai Soft X-ray FEL project are presented. Compared with a TGU modulator, using the natural gradient of a normal planar modulator has the distinct advantage that the gradient can be conveniently tuned in quite a large range by adjusting the beam orbit offset. [ABSTRACT FROM AUTHOR]

The Paul Scherrer Institute is implementing laser-based seeding in the soft X-ray beamline (Athos) of its free-electron laser, SwissFEL, to enhance the temporal and spectral properties of the delivered photon pulses. This technique requires, among other components, two identical modulators for coupling the electron beam with an external laser with a wavelength range between 260 and 1600 nm. The design, magnetic measurements results, alignment, operation and also details of the novel and exotic magnetic configuration of the prototype are described. [ABSTRACT FROM AUTHOR]

This report presents testing of a prototype cantilevered liquid-nitrogen-cooled silicon mirror. This mirror was designed to be the first mirror for the new soft X-ray beamlines to be built as part of the Advanced Light Source Upgrade. Test activities focused on fracture, heat transfer, modal response and distortion, and indicated that the mirror functions as intended. [ABSTRACT FROM AUTHOR]

Soft X‐ray imaging is a new method used to observe the structure of the Earth's magnetosphere. Reconstruction of the Earth's three‐dimensional (3‐D) magnetospheric structure from 2‐D soft X‐ray images is an important research topic in astronomical imaging and exploration. In this study, computed tomography (CT) is investigated for application to the planned Solar wind Magnetosphere Ionosphere Link Explorer (SMILE), where resulting images are collected at varying small angles. The restricted geometry of SMILE results in sparse projection data and reduced reconstruction quality. As such, a new algorithm is proposed, based on cone‐beam computed tomography (CBCT) and utilizing 3‐D generative adversarial networks (GAN) to supplement the 2‐D soft X‐ray images and increase the angular coverage of the projections. A complement optimization backpropagation network (COBN) is then used to reconstruct high‐quality 3‐D X‐ray emissivity profiles in the magnetosphere. A series of validation experiments were conducted in which the reconstructions were compared with synthetic results generated by the PPMLR‐MHD (an extended LagRangian version of the Piecewise Parabolic Method –MagnetoHydroDynamic) model under varying solar wind conditions. Results showed the supplemented profiles were more complete and accurate than the direct reconstructions, as measured by the peak signal‐to‐noise ratio (PSNR) and structural similarity (SSIM). This suggests the proposed technique could be a viable approach to observing magnetosphere structure and variability. Key Points: A new method is proposed for reconstructing 3‐D magnetospheric X‐ray emissivity data from multi‐angle 2‐D soft X‐ray imagesA machine learning method was applied to supplement 2‐D soft X‐ray images collected at limited anglesThis method was validated using 3‐D magnetospheric X‐ray emissivity data from the 3‐D PPMLR‐MHD model [ABSTRACT FROM AUTHOR]

Summary: This paper presents feasibility studies in utilizing graphics processing units (GPUs) as high‐performance computing hardware with front‐end electronics in high‐scale magnetic confinement thermal fusion experiments. The objective of the research is to provide scalable, high‐throughput, and low‐latency measurements for the runtime tokamak metallic impurities X‐ray diagnostic for the Tungsten Environment in Steady‐State Tokamak (WEST) reactor. The heterogeneous system of front‐end with field‐programmable gate arrays and the back‐end server was introduced to decompose workloads efficiently. It allows the comprehensive evaluation of CPUs and accelerators. In particular, a novel implementation of the back‐end algorithm for GPU with the performance analysis are presented. [ABSTRACT FROM AUTHOR]

Positron emission tomography/magnetic resonance imaging (PET/MRI) potentially offers several advantages over positron emission tomography/computed tomography (PET/CT), for example, no CT radiation dose and soft tissue images from MR acquired at the same time as the PET. However, obtaining accurate linear attenuation correction (LAC) factors for the lung remains difficult in PET/MRI. LACs depend on electron density and in the lung, these vary significantly both within an individual and from person to person. Current commercial practice is to use a single‐valued population‐based lung LAC, and better estimation is needed to improve quantification. Given the under‐appreciation of lung attenuation estimation as an issue, the inaccuracy of PET quantification due to the use of single‐valued lung LACs, the unique challenges of lung estimation, and the emerging status of PET/MRI scanners in lung disease, a review is timely. This paper highlights past and present methods, categorizing them into segmentation, atlas/mapping, and emission‐based schemes. Potential strategies for future developments are also presented. [ABSTRACT FROM AUTHOR]

Elliptical polarized undulators (EPUs) are broadly used in the soft X‐ray energy range. They have the advantage of providing photons with both varied energy and polarization through adjustments to the value of the gap and/or shift magnet arrays in an undulator. Yet these adjustments may create a disturbance on the stability of the electron beam in a storage ring. To correct such a disturbance, it is necessary to establish a feed‐forward table of key nodes in the gap‐shift‐defined two‐dimensional parameter space. Such a table can only be scanned during machine‐study time. For a free‐walking mode, whereby an undulator is allowed to manoeuvre in the whole gap‐shift space, all the key nodes need to be scanned at the expense of a large amount of machine‐study time. This will greatly delay the employment of a full‐polarization capable undulator (especially circularly polarized). By analyzing data‐collecting patterns of user experiments, this paper defines a reduced set of key nodes in gap‐shift parameter space, with the number of key nodes to be scanned for feed‐forwarding scaled down to one‐third of the original; and introduces a new walking mode for EPUs: confined‐walking mode, whereby the undulator is manoeuvred only within the reduced set of key nodes. Such a mode is firstly realized on the EPUs at the DREAMLINE beamline at Shanghai Synchrotron Radiation Facility (SSRF). Under confined‐walking mode, the undulator movements are stable and there is no obvious disturbance to the electron beam with the feed‐forward system in operation. Successful experiments have been carried out using the circularly polarized light obtained via the new walking mode. This mode is expected to be applied to future EPUs at SSRF with the increasing requirements for various polarization modes. [ABSTRACT FROM AUTHOR]

A picosecond pump-probe resonant soft X-ray scattering measurement system has been developed at the Photon Factory storage ring for highly efficient data collection. A high-repetition-rate high-power compact laser system has been installed to improve efficiency via flexible data acquisition to a sub-MHz frequency in time-resolved experiments. Data are acquired by gating the signal of a channel electron multiplier with a pulse-counting mode capable of discriminating single-bunch soft X-ray pulses in the dark gap of the hybrid operation mode in the storage ring. The photoinduced dynamics of magnetic order for multiferroic manganite SmMn2O5 are clearly demonstrated by the detection of transient changes in the resonant soft X-ray scattering intensity around the Mn LIII- and O K-edges. [ABSTRACT FROM AUTHOR]

Soft X-ray monochromators for synchrotron radiation sources have been continuously developed over the years, improving energy resolution and stability. Great effort has been made in improving the surface quality of the optics involved, reaching values permitting diffraction-limited images. Still, one problem has not been solved, nor fully understood, yet: groove placing errors. Nowadays, these are one of the major factors responsible for resolving the power reduction of diffraction-gratings-based X-ray monochromators. Despite decades of use of gratings, there is not yet a universally established method for predicting and simulating the effect of groove placing errors on monochromator performance. This is especially important in the new scenario of high-coherent X-ray sources, i.e. diffraction-limited storage rings and free-electron lasers. To address this problem, in this article an approach based on WISER (Wavefront propagatIon Simulation codE libRary) is presented. WISER is a physical optics simulation package, also available in the user-friendly Orange Synchrotron Radiation Suite - OASYS. Even though it was originally conceived to assess the focusing performance of X-ray mirrors in the presence of height defects, it perfectly simulates the performance of a periodic (or quasi-periodic) structure like a diffraction grating. In this article, the way to use WISER and its application to a specific case, e.g. the design of a monochromator for the upgrade of a beamline at the Advanced Light Source, are shown. A simple rule for estimating how well the grooves are placed on a grating, based on calculation of the Strehl ratio, is also presented. [ABSTRACT FROM AUTHOR]

Although sodium‐ion batteries (SIBs) offer promising low‐cost alternatives to lithium‐ion batteries (LIBs), several challenges need to be overcome for their widespread adoption. A primary concern is the optimization of carbon anodes. Graphite, vital to the commercial viability of LIBs, has a limited capacity for sodium ions. Numerous alternatives to graphite are explored, particularly focusing on disordered carbons, including hard carbon. However, compared with graphite, most of these materials underperform in LIBs. Furthermore, the reaction mechanism between carbon and sodium ions remains ambiguous owing to the structural diversity of disordered carbon. A straightforward mechanical approach is introduced to enhance the sodium ion storage capacity of graphite, supported by comprehensive analytical techniques. Mechanically activated graphite delivers a notable reversible capacity of 290.5 mAh·g−1 at a current density of 10 mA·g−1. Moreover, it maintains a capacity of 157.7 mAh·g−1 even at a current density of 1 A·g−1, benefiting from the defect‐rich structure achieved by mechanical activation. Soft X‐ray analysis revealed that this defect‐rich carbon employs a sodium‐ion storage mechanism distinct from that of hard carbon. This leads to an unexpected reversible reaction on the solid electrolyte surface. These insights pave the way for innovative design approaches for carbon electrodes in SIB anodes. [ABSTRACT FROM AUTHOR]

Monochromators for synchrotron radiation beamlines typically use perfect crystals for the hard X-ray regime and gratings for soft X-rays. There is an intermediate range, typically 1-3 keV (tender X-rays), which common perfect crystals have difficulties covering and gratings have low efficiency, although some less common crystals with high d-spacing could be suitable. To evaluate the suitability of these crystals for a particular beamline, it is useful to evaluate the crystals' performance using tools such as ray-tracing. However, simulations for double-crystal monochromators are only available for the most used crystals such as Si, Ge or diamond. Here, an upgrade of the SHADOW ray-tracing code and complementary tools in the OASYS suite are presented to simulate high dspacing crystals with arbitrary, and sometimes complex, structures such as beryl, YB66, muscovite, etc. Isotropic and anisotropic temperature factors are also considered. The YB66 crystal with 1936 atomic sites in the unit cell is simulated, and its applicability for tender X-ray monochromators is discussed in the context of new low-emittance storage rings. [ABSTRACT FROM AUTHOR]

Boron carbide is a prominent material for high-brilliance synchrotron optics as it remains stable up to very high temperatures. The present study shows a significant change taking place at 550 °C in the buried interface region formed between the Cr adhesive layer and the native oxide layer present on the silicon substrate. An in situ annealing study is carried out at the Indus-1 Reflectivity beamline from room temperature to 550°C (100°C steps). The studied sample is a mirror-like boron carbide thin film of 400 A ° thickness deposited with an adhesive layer of 20 A ° Cr on a silicon substrate. The corresponding changes in the film structure are recorded using angle-dependent soft X-ray reflectivity measurements carried out in the region of the boron K-edge after each annealing temperature. Analyses performed using the Parratt recursive formalism reveal that the top boron carbide layer remains intact but interface reactions take place in the buried Cr-SiO2 region. After 300°C the Cr layer diffuses towards the substrate. At higher temperatures of 500°C and 550 °C the Cr reacts with the native oxide layer and tends to form a low-density compound of chromium oxysilicide (CrSiOx). Depth profiling of Si and Cr distributions obtained from secondary ion mass spectroscopy measurements corroborate the layer model obtained from the soft X-ray reflectivity analyses. Details of the interface reaction taking place near the substrate region of boron carbide/Cr sample are discussed. [ABSTRACT FROM AUTHOR]

The newly constructed time-resolved atomic, molecular and optical science instrument (TMO) is configured to take full advantage of both linear accelerators at SLAC National Accelerator Laboratory, the copper accelerator operating at a repetition rate of 120 Hz providing high per-pulse energy as well as the superconducting accelerator operating at a repetition rate of about 1 MHz providing high average intensity. Both accelerators power a soft X-ray freeelectron laser with the new variable-gap undulator section. With this flexible light source, TMO supports many experimental techniques not previously available at LCLS and will have two X-ray beam focus spots in line. Thereby, TMO supports atomic, molecular and optical, strong-field and nonlinear science and will also host a designated new dynamic reaction microscope with a submicrometer X-ray focus spot. The flexible instrument design is optimized for studying ultrafast electronic and molecular phenomena and can take full advantage of the sub-femtosecond soft X-ray pulse generation program. [ABSTRACT FROM AUTHOR]

Strongly magnetized isolated neutron stars (NSs) are categorized into two families according, mainly, to their magnetic field strength. The one with a higher magnetic field of 1014–1015 Gauss is called "magnetar," and the other is the X‐ray isolated neutron star (XINS) with 1013 Gauss. Both magnetars and XINSs show thermal emission in X‐rays, whose spectra are different. The soft X‐ray spectrum (below 10 keV) of a magnetar is reproduced with a two‐temperature blackbody (2BB), whereas that of an XINS shows only a single‐temperature blackbody (1BB), and its temperature is even lower than that of magnetars. On the basis of the magnetic field and temperature, it is often speculated that XINSs may be old and cooled magnetars. However, no other strong observational evidence has yet been reported to support the speculation. Here, we report that all the seven known XINSs show high‐temperature emission, which should have a similar origin to that of magnetars. Analyzing all the XMM‐Newton data of the XINSs with the highest statistics ever achieved, we find that their X‐ray spectra are all reproduced with a 2BB model, similar to magnetars, as opposed to the traditional 1BB model. Their emission radii and temperature ratios are also similar to those of magnetars except for two XINSs, which show significantly smaller radii than the others. The remarkable similarity in the X‐ray spectra between XINSs and magnetars suggests that the origins of their emitting regions are also the same. The lower temperature in XINSs can be explained if XINSs are older than magnetars. Therefore, this result is another observational indication that supports the standard hypothesis of classification of highly magnetized NSs. This article is based on our paper Yoneyama et al. (2019; accepted to PASJ). [ABSTRACT FROM AUTHOR]

The use of soft X-rays near the carbon edge of absorption (270-300 eV) greatly enhances studies in various branches of science. However, the choice of reflecting coatings for mirrors operating in free-electron and X-ray free-electron laser (FEL and XFEL) beamlines in this spectral range is not so evident and experimental justifications of the mirror efficiency are rather limited. In the present paper it is demonstrated experimentally that the reflectivity of B4C- and Ni-coated grazing-incidence mirrors is high enough for their operation in FEL or XFEL beamlines near the carbon K-edge of absorption. The minimal reflectivity of both mirrors proves to exceed 80% near the carbon absorption edge at a grazing angle of 0.6°. An in-depth profile of the chemical elements composing the reflecting coatings is reconstructed based on analysis of a set of reflectivity curves measured versus the grazing angle at different photon energies in the soft X-ray spectral region. This allows us to predict correctly the mirror reflectivity at any X-ray energy and any grazing angle. [ABSTRACT FROM AUTHOR]

We present an initial assessment of using tomography on single‐spacecraft images to reconstruct 3D X‐ray emissions from the Earth's magnetosheath. 3D structures in the Earth's magnetosphere have been studied using superposed epoch techniques with single‐point single‐spacecraft observations. They have yielded great insights, but some studies are observation starved, particularly for infrequent solar wind conditions. Global imaging data have provided more insight about these structures, but are 2D projections of 3D structures. We explore the use of tomographic reconstruction techniques to understand what can be extracted from global images from a single spacecraft. The Solar wind Magnetosphere Ionosphere Link Explorer mission, due to launch in 2024 on a 3‐year mission, will carry a soft X‐ray imager which will capture emissions from portions of the magnetosheath and upstream solar wind. We already demonstrated that the 3D shape of the magnetopause and the bow shock can be extracted from such images with suitable assumptions. The next step is to examine whether full 3D reconstructions of the emissions are possible. We explore the limited range of viewing angles, which affect the accuracy of the reconstructions and introduce artifacts in some cases, and the low count‐rates in the images which introduce noise in the reconstructions which must be filtered out. Despite these limitations we show that it is possible to reconstruct some aspects of the magnetosheath global morphology using single‐spacecraft soft X‐ray imaging. Key Points: Tomographic reconstruction of the magnetosheath with Solar wind Magnetosphere Ionosphere Link Explorer is possibleHigh noise/low‐count images can be used with regularization constraintsSuperposed epoch over a year works better than a single orbit [ABSTRACT FROM AUTHOR]

Ni–Fe‐based oxides are among the most promising catalysts developed to date for the bottleneck oxygen evolution reaction (OER) in water electrolysis. However, understanding and mastering the synergy of Ni and Fe remain challenging. Herein, we report that the synergy between Ni and Fe can be tailored by crystal dimensionality of Ni, Fe‐contained Ruddlesden–Popper (RP)‐type perovskites (La0.125Sr0.875)n+1(Ni0.25Fe0.75)nO3n+1 (n = 1, 2, 3), where the material with n = 3 shows the best OER performance in alkaline media. Soft X‐ray absorption spectroscopy spectra before and after OER reveal that the material with n = 3 shows enhanced Ni/Fe–O covalency to boost the electron transfer as compared to those with n = 1 and n = 2. Further experimental investigations demonstrate that the Fe ion is the active site and the Ni ion is the stable site in this system, where such unique synergy reaches the optimum at n = 3. Besides, as n increases, the proportion of unstable rock‐salt layers accordingly decreases and the leaching of ions (especially Sr2+) into the electrolyte is suppressed, which induces a decrease in the leaching of active Fe ions, ultimately leading to enhanced stability. This work provides a new avenue for rational catalyst design through the dimensional strategy. [ABSTRACT FROM AUTHOR]

The beamline optics and endstations at branch B of the Versatile Soft X-ray (VerSoX) beamline B07 at Diamond Light Source are described. B07-B provides medium-flux X-rays in the range 45-2200 eV from a bending magnet source, giving access to local electronic structure for atoms of all elements from Li to Y. It has an endstation for high-throughput X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine-structure (NEXAFS) measurements under ultrahigh-vacuum (UHV) conditions. B07-B has a second endstation dedicated to NEXAFS at pressures from UHV to ambient pressure (1 atm). The combination of these endstations permits studies of a wide range of interfaces and materials. The beamline and endstation designs are discussed in detail, as well as their performance and the commissioning process. [ABSTRACT FROM AUTHOR]

The soft X-ray photoelectron momentum microscopy (PMM) experimental station at the UVSOR Synchrotron Facility has been recently upgraded by additionally guiding vacuum ultraviolet (VUV) light in a normal-incidence configuration. PMM offers a very powerful tool for comprehensive electronic structure analyses in real and momentum spaces. In this work, a VUV beam with variable polarization in the normal-incidence geometry was obtained at the same sample position as the soft X-ray beam from BL6U by branching the VUV beamline BL7U. The valence electronic structure of the Au(111) surface was measured using horizontal and vertical linearly polarized (s-polarized) light excitations from BL7U in addition to horizontal linearly polarized (p-polarized) light excitations from BL6U. Such highly symmetric photoemission geometry with normal incidence offers direct access to atomic orbital information via photon polarization-dependent transition-matrix-element analysis. [ABSTRACT FROM AUTHOR]

Joule heating is one of the main energy inputs into the thermosphere‐ionosphere system. Precise modeling of this process is essential for any space weather application. Existing thermosphere‐ionosphere models tend to underestimate the actual Joule heating rate quite significantly. The Thermosphere‐Ionosphere‐Electrodynamics General‐Circulation‐Model applies an empirical scaling factor of 1.5 for compensation. We calculate vertical profiles of Joule heating rates from approximately 2,220 hr of measurements with the EISCAT incoherent scatter radar and the corresponding model runs. We investigate model runs with the plasma convection driven by both the Heelis and the Weimer model. The required scaling of the Joule heating profiles is determined with respect to the Kp index, the Kan‐Lee merging electric field EKL, and the magnetic local time. Though the default scaling factor of 1.5 appears to be adequate on average, we find that the required scaling varies strongly with all three parameters ranging from 0.46 to ∼20 at geomagnetically disturbed and quiet times, respectively. Furthermore, the required scaling is significantly different in runs driven by the Heelis and Weimer model. Adjusting the scaling factor with respect to the Kp index, EKL, the magnetic local time, and the choice of convection model would reduce the difference between Joule heating rates calculated from measurement and model plasma parameters. Plain Language Summary: The vast majority of the energy input to the Earth system originates from the sun. This includes the absorption of various types of radiation, for example, ultraviolet radiation in the ozone layer or visible light and infrared radiation at the surface. In the upper atmosphere above about 80 km altitude, the absorption of extreme ultraviolet radiation and soft X‐rays plays a major role. However, other processes also contribute significantly to the heating of this region, for example, the energy dissipation in the form of electric currents flowing along electric fields, also known as Joule heating. Joule heating is highly variable and can be drastically enhanced especially during solar storms, which can have potentially disastrous effects on satellites. Accurate modeling, and therefore also prediction, of Joule heating is not possible at the moment since thermosphere‐ionosphere models have to scale the Joule heating empirically to fit the actual values. We investigate how the required scaling changes under different geophysical conditions. Key Points: The constant Joule heating scaling factor in TIE‐GCM is inadequate to compensate for the underestimation under various geomagnetic conditionsJoule heating rates calculated from 2,220 hr of EISCAT measurements are compared to TIE‐GCM runs driven with the Heelis and Weimer convection modelsThe required scaling factor varies significantly with the Kp index, the Kan‐Lee merging electric field, and the magnetic local time [ABSTRACT FROM AUTHOR]

Imaging of actin filaments is crucial due to the integral role that they play in many cellular functions such as intracellular transport, membrane remodelling and cell motility. Visualizing actin filaments has so far relied on fluorescence microscopy and electron microscopy/tomography. The former lacks the capacity to capture the overall local ultrastructure, while the latter requires rigorous sample preparation that can lead to potential artefacts, and only delivers relatively small volumes of imaging data at the thinnest areas of a cell. In this work, a correlative approach utilizing in situ super‐resolution fluorescence imaging and cryo X‐ray tomography was used to image bundles of actin filaments deep inside cells under near‐native conditions. In this case, fluorescence 3D imaging localized the actin bundles within the intracellular space, while X‐ray tomograms of the same areas provided detailed views of the local ultrastructure. Using this new approach, actin trails connecting vesicles in the perinuclear area and hotspots of actin presence within and around multivesicular bodies were observed. The characteristic prevalence of filamentous actin in cytoplasmic extensions was also documented. [ABSTRACT FROM AUTHOR]

Hepatitis C virus (HCV) is an enveloped RNA virus. One of the hallmarks of HCV infection is a rearrangement of the host cell membranes, known as the 'membranous web'. Full‐field cryo soft X‐ray tomography (cryo‐SXT) in the water‐window energy range (284–543 eV) was performed on the MISTRAL beamline to investigate, in whole unstained cells, the morphology of the membranous rearrangements induced in HCV replicon‐harbouring cells in conditions close to the living physiological state. All morphological alterations could be reverted by a combination of sofosbuvir/daclatasvir, which are clinically approved antivirals (direct‐acting antivirals; DAAs) for HCV infection. Correlatively combining cryo‐SXT and 2D synchrotron‐based infrared microscopy provides critical information on the chemical nature of specific infection‐related structures, which allows specific patterns of the infection process or the DAA‐mediated healing process to be distinguished. [ABSTRACT FROM AUTHOR]