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The SASE3 soft X-ray beamline at the European XFEL has been designed and built to provide experiments with a pink or monochromatic beam in the photon energy range 250–3000 eV. Here, the focus is monochromatic operation of the SASE3 beamline, and the design and performance of the SASE3 grating monochromator are reported. The unique capability of a free-electron laser source to produce short femtosecond pulses of a high degree of coherence challenges the monochromator design by demanding control of both photon energy and temporal resolution. The aim to transport close to transform-limited pulses poses very high demands on the optics quality, in particular on the grating. The current realization of the SASE3 monochromator is discussed in comparison with optimal design performance. At present, the monochromator operates with two gratings: the low-resolution grating is optimized for time-resolved experiments and allows for moderate resolving power of about 2000–5000 along with pulse stretching of a few to a few tens of femtoseconds RMS, and the high-resolution grating reaches a resolving power of 10 000 at the cost of larger pulse stretching.

Abstract Ion irradiation is a widely employed tool to fabricate diamond micro- and nano-structures for applications in integrated photonics and quantum optics. In this context, it is essential to accurately assess the effect of ion-induced damage on the variation of the refractive index of the material, both to control the side effects in the fabrication process and possibly finely tune such variations. Several partially contradictory accounts have been provided on the effect of the ion irradiation on the refractive index of single crystal diamond. These discrepancies may be attributable to the fact that in all cases the ions are implanted in the bulk of the material, thus inducing a series of concurrent effects (volume expansion, stress, doping, etc.). Here we report the systematic characterization of the refractive index variations occurring in a 38 µm thin artificial diamond sample upon irradiation with high-energy (3 MeV and 5 MeV) protons. In this configuration the ions are fully transmitted through the sample, while inducing an almost uniform damage profile with depth. Therefore, our findings conclusively identify and accurately quantify the change in the material polarizability as a function of ion beam damage as the primary cause for the modification of its refractive index.

Chlorination is widely used to prevent biological fouling in power station cooling water systems. It may impact non-target organisms both within the cooling system and after discharge (primary and secondary entrainment). However, there is a lack of data on the impacts of the low chlorine concentrations that occur in the discharged plume on marine phytoplankton community structure and function. We examine the impacts on natural phytoplankton communities of single and multiple exposures to chlorination at concentrations between 0.02 and 0.1 mg/L total residual oxidants (TRO). Low-level chlorination causes limited changes in diversity and has no impact on total biomass. However, changes in size structure and functional diversity quantified using flow cytometry do show a reduction in smaller cells, particularly eukaryote picophytoplankton. These impacts are not detectable using chlorophyll a concentration alone, so flow cytometry provides important additional information over more standard ecotoxicological methods. The effects are likely to be localised in the vicinity of the discharges (mixing zone) where the environmental quality standard (EQS) of 10 μg/L for chlorine is exceeded, but impacts on coastal food webs and biogeochemical cycles should be further evaluated., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Crown Copyright © 2024. Published by Elsevier Ltd. All rights reserved.)

Xray free-electron lasers (XFELs) enable experiments that would have been impractical or impossible at conventional X-ray laser facilities. Indeed, more XFEL facilities are being built and planned, with their aim to deliver larger pulse energies and higher peak brilliance. While seeking to increase the pulse power, it is quintessential to consider the maximum pulse fluence that a grazing-incidence FEL mirror can withstand. To address this issue, several studies were conducted on grazing-incidence damage by soft X-ray FEL pulses at the European XFEL facility. Boron carbide (B 4 C) coatings on polished silicon substrate were investigated using 1 keV photon energy, similar to the X-ray mirrors currently installed at the soft X-ray beamlines (SASE3). The purpose of this study is to compare the damage threshold of B 4 C and Si to determine the advantages, tolerance and limits of using B 4 C coatings., (open access.)

The Small Quantum Systems instrument is one of the six operating instruments of the European XFEL, dedicated to the atomic, molecular and cluster physics communities. The instrument started its user operation at the end of 2018 after a commissioning phase. The design and characterization of the beam transport system are described here. The X-ray optical components of the beamline are detailed, and the beamline performances, transmission and focusing capabilities are reported. It is shown that the X-ray beam can be effectively focused as predicted by ray-tracing simulations. The impact of non-ideal X-ray source conditions on the focusing performances is discussed., (open access.)

The United Nations (UN) recognises free school meals as critical, yet widely disrupted by COVID-19. We investigate caregiver perceptions and responses to interruptions to the universal infant free school meal programme (UIFSM) in Cambridgeshire, England, using an opt-in online survey. From 586 responses, we find 21 per cent of respondents' schools did not provide UIFSM after lockdown or advised caregivers to prepare packed lunches. Where provided, caregivers perceived a substantial decline in quality and variety of meals, influencing uptake. Direction to bring packed lunches, which caregivers reported to have contained ultra-processed foods of lower nutritional quality, influenced caregiver behaviour rather than safety concerns as claimed by industry. The quality and variety of meals, and school and government policy, had greater impact than concerns for safety. In the UK and at the international level, policymakers, local governments, and schools must act to reverse the trend of ultra-processed foods in packed lunches, while improving the perceived quality of meals provided at schools., (© 2023. The Author(s), under exclusive licence to Springer Nature Limited.)

The SASE3 soft X-ray beamline at the European XFEL has been designed and built to provide experiments with a pink or monochromatic beam in the photon energy range 250-3000 eV. Here, the focus is monochromatic operation of the SASE3 beamline, and the design and performance of the SASE3 grating monochromator are reported. The unique capability of a free-electron laser source to produce short femtosecond pulses of a high degree of coherence challenges the monochromator design by demanding control of both photon energy and temporal resolution. The aim to transport close to transform-limited pulses poses very high demands on the optics quality, in particular on the grating. The current realization of the SASE3 monochromator is discussed in comparison with optimal design performance. At present, the monochromator operates with two gratings: the low-resolution grating is optimized for time-resolved experiments and allows for moderate resolving power of about 2000-5000 along with pulse stretching of a few to a few tens of femtoseconds RMS, and the high-resolution grating reaches a resolving power of 10 000 at the cost of larger pulse stretching., (open access.)

A real-time and accurate characterization of the X-ray beam size is essential to enable a large variety of different experiments at free-electron laser facilities. Typically, ablative imprints are employed to determine shape and size of µm-focused X-ray beams. The high accuracy of this state-of-the-art method comes at the expense of the time required to perform an ex-situ image analysis. In contrast, diffraction at a curved grating with suitably varying period and orientation forms a magnified image of the X-ray beam, which can be recorded by a 2D pixelated detector providing beam size and pointing jitter in real time. In this manuscript, we compare results obtained with both techniques, address their advantages and limitations, and demonstrate their excellent agreement. We present an extensive characterization of the FEL beam focused to ≈1 µm by two Kirkpatrick-Baez (KB) mirrors, along with optical metrology slope profiles demonstrating their exceptionally high quality. This work provides a systematic and comprehensive study of the accuracy provided by curved gratings in real-time imaging of X-ray beams at a free-electron laser facility. It is applied here to soft X-rays and can be extended to the hard X-ray range. Furthermore, curved gratings, in combination with a suitable detector, can provide spatial properties of µm-focused X-ray beams at MHz repetition rate.

The Severn Estuary is a large macrotidal estuary which includes an extensive mudflat with microphytobenthos (MPB) playing a key role in the ecosystem. This study evaluated the impact of chlorination at two different dosing levels (0.05 and 0.5 mg/l as total residual oxidants, TRO, representative of potential concentrations in the mixing zone and within the cooling water systems of a power station) on a MPB community representative of the Severn Estuary. Biomass and diversity were not negatively impacted while physiology was partially affected at the beginning of the experiment, and it recovered towards the end of the experiment. Further investigations for diversity are needed to consolidate our findings. In conclusion our results show that MPB is resilient to chlorination up to a concentration of 0.5 mg/l which is much higher (>10 times) than what might be expected near the chlorinated discharges for most coastal power stations., (Crown Copyright © 2022. Published by Elsevier Ltd. All rights reserved.)

Chlorination is a widely used method to prevent biofouling in power station cooling water systems in coastal and estuarine environments. This study evaluated the impact of chlorination together with temperature increase to simulate primary entrainment of a phytoplankton community. Biomass, diversity, and photosynthetic activity were monitored over 72 hours to establish impacts on the phytoplankton community. Biomass was significantly reduced after treatment. The mean cell size of the population significantly increased immediately after treatment highlighting an impact on the smaller cell size species of the community (picophytoplankton). Changes in accessory pigments composition suggest an effect on groups such as Prasinophyceae, Cyanobacteria and Chlorophycea. Species composition, dominated by diatoms, was also affected with Skeletonema marinoi and Asterionellopsis glacialis amongst the most sensitive species. Photosynthetic activity was affected in the short term but recovered after 48 hours. This study shows that by using a combination of measurements (e.g biomass, diversity, and physiology) the effects of entrainment in power station cooling water systems, that may be of longer-term significance for specific functional groups of phytoplankton communities, can be discerned. These changes would not necessarily be seen using individual techniques alone such as cell number counts or biomass assessment which may indicate apparent community recovery., (Copyright © 2021. Published by Elsevier B.V.)

Seagrasses are globally important, but their extent is decreasing due to the impact of human activities and changing climatic conditions. Seagrass meadows provide vital services, but their condition and distribution are not yet well known, particularly in many small tropical Pacific islands. In 2018, observations and samples were collected from intertidal seagrasses of Efate Island, Vanuatu (South Pacific). Observations included canopy height, percentage cover, growth rate and species variety. Water quality samples were also collected in some locations. Our seagrass metrics suggested more challenging conditions for the seagrasses near Port Vila, the main urban area in the island, where water quality analyses indicated higher levels of dissolved inorganic nitrogen and suspended solids., (Crown Copyright © 2020. Published by Elsevier Ltd. All rights reserved.)

Objectives: Restricting mobility is a central aim for lowering contact rates and preventing COVID-19 transmission. Yet the impact on mobility of different non-pharmaceutical countermeasures in the earlier stages of the pandemic is not well-understood., Design: Trends were evaluated using Citymapper's mobility index covering 2nd to 26th March 2020, expressed as percentages of typical usage periods from 0% as the lowest and 100% as normal. China and India were not covered. Multivariate fixed effects models were used to estimate the association of policies restricting movement on mobility before and after their introduction. Policy restrictions were assessed using the Oxford COVID-19 Government Response Stringency Index as well as measures coding the timing and degree of school and workplace closures, transport restrictions, and cancellation of mass gatherings., Setting: 41 cities worldwide., Main Outcome Measures: Citymapper's mobility index., Results: Mobility declined in all major cities throughout March. Larger declines were seen in European than Asian cities. The COVID-19 Government Response Stringency Index was strongly associated with declines in mobility (r = - 0.75, p < 0.001). After adjusting for time-trends, we observed that implementing non-pharmaceutical countermeasures was associated with a decline of mobility of 10.0% for school closures (95% CI: 4.36 to 15.7%), 15.0% for workplace closures (95% CI: 10.2 to 19.8%), 7.09% for cancelling public events (95% CI: 1.98 to 12.2%), 18.0% for closing public transport (95% CI: 6.74 to 29.2%), 13.3% for restricting internal movements (95% CI: 8.85 to 17.8%) and 5.30% for international travel controls (95% CI: 1.69 to 8.90). In contrast, as expected, there was no association between population mobility changes and fiscal or monetary measures or emergency healthcare investment., Conclusions: Understanding the effect of public policy on mobility in the early stages is crucial to slowing and reducing COVID-19 transmission. By using Citymapper's mobility index, this work provides the first evidence about trends in mobility and the impacts of different policy interventions, suggesting that closure of public transport, workplaces and schools are particularly impactful.

Objectives: Transgender-identifying sex workers (TGISWs) are among the most vulnerable groups but are rarely the focus of health research. Here we evaluated perceived barriers to healthcare access, risky sexual behaviours and exposure to violence in the United Kingdom (UK), based on a survey of all workers on BirchPlace, the main transgender sex commerce website in the UK., Study Design: The study design used in the study is an opt-in text-message 12-item questionnaire., Methods: Telephone contacts were harvested from BirchPlace's website (n = 592 unique and active numbers). The questionnaire was distributed with Qualtrics software, resulting in 53 responses., Results: Our survey revealed significant reported barriers to healthcare access, exposure to risky sexual behaviours and to physical violence. Many transgender sex workers reportedly did not receive a sexual screening, and 28% engaged in condomless penetrative sex within the preceding six months, and 68% engaged in condomless oral sex. 17% responded that they felt unable to access health care they believed medically necessary. Half of the participants suggested their quality of life would be improved by law reform., Conclusions: TGISWs report experiencing a high level of risky sexual behaviour, physical violence and inadequate healthcare access. Despite a National Health System, additional outreach may be needed to ensure access to services by this population., (Copyright © 2020 The Authors. Published by Elsevier Ltd.. All rights reserved.)

The European XFEL requires long and ultraflat X-ray mirrors of high precision for the beam offset and distribution system [Altarelli et al. (2006), XFEL Technical Design Report, DESY 2006-097. DESY, Hamburg, Germany]. A general specification of the beam transport mirrors is a length of up to 950 mm and an optical surface with a deviation from a perfectly flat surface of <30 nm peak-to-valley and a figure error of <2 nm peak-to-valley. From a production point of view, such a mirror cannot be easily fabricated so, in each beamline, it is foreseen to have at least one mirror with bending capabilities. In this way, it is possible to correct the residual divergence of the beam in order to focus it in the correct position with high accuracy and repeatability. This is practically implemented using a mechanical bender in which the mirror is mounted and bent through a motorized actuator. One such system was characterized in the metrology lab using a large-aperture Fizeau interferometer and a capacitive sensor. It was then installed in the beamline and calibrated again using the X-ray beam. Here, the procedure is described and the two different methods are compared, stressing the differences and the possible explanations and improvements., (open access.)

SASE1 is the first beamline of the European XFEL that became operational in 2017. It consists of the SASE1 undulator system, the beam transport system, and the two scientific experiment stations: Single Particles, Clusters, and Biomolecules and Serial Femtosecond Crystallography (SPB/SFX), and Femtosecond X-ray Experiments (FXE). The beam transport system comprises mirrors to offset and guide the beam to the instruments and a set of X-ray optical components to align, manipulate and diagnose the beam. The SASE1 beam transport system is described here in its initial configuration, and results and experiences from the first year of user operation are reported.

The European XFEL is a large x-ray free-electron laser facility under construction in the Hamburg area of Germany. It is designed to provide a transversally fully coherent x-ray radiation with outstanding characteristics: high repetition rate (up to 2700 pulses with a 0.6 ms long pulse train at 10 Hz, for a total of 27 000 pulses/s), short wavelength (down to 0.05 nm), short pulse (in the femtosecond scale), and high average brilliance [1.6 × 10 25 photons/s/(mm 2 /mrad 2 )/0.1% bandwidth]. Five main beamlines are foreseen, with three fully financed and installed, called SASEs (from "self-amplified spontaneous-emission"): SASE1 (hard x-rays, 3-25 KeV), SASE2 (hard x-rays, 3 to possibly 60 KeV with the use of a third harmonic), and SASE3 (soft x-rays, 0.3-3 KeV). For each beamline, two separate scientific instruments will be served using the beam alternately in 24-h, 7-day shifts. The installation and commissioning of the European XFEL beamlines are proceeding rapidly. So far, the hard x-ray SASE1 beamline and the soft x-ray SASE3 beamline, both injected with the same electron beam, have been installed and fully commissioned. SASE1 already delivers beam to the corresponding stations and has been open for external users since September 2017. The SASE3 beamline was successfully commissioned in February 2018, and the simultaneous operation of SASE3 and SASE1 was also demonstrated. In the meantime, the SASE2 beamline is being equipped and will be commissioned starting October 2018. We present the last results in the SASE1 and SASE3 beam transport, taking consideration in particular of the metrology carried out before the installation, the installation itself, and the final commissioning. The different stages were crucial to have good quality optical beam and fast commissioning to proceed with the delivery to experiments and users.

Chlorination is a widely used antifouling method for freshwater and marine applications. Chlorine added to seawater reacts to form oxidants that are toxic to biofouling organisms. Further, the oxidants that result are short-lived, but may nevertheless affect non-target species in waterbodies receiving the antifouling effluent. This study evaluated the toxicity of chlorinated seawater (e.g. following sodium hypochlorite addition) on two different species of marine benthic diatoms (Achnanthes spp., and Navicula pelliculosa), which are representative of microphytobenthos communities - an important component in coastal habitats that may be exposed to chlorinated seawater. To evaluate the growth inhibition over a 72 h period, algae were immobilised in alginate beads and exposed to different levels of chlorination in a flow through system. Growth rates and physiological condition of the microalgae were evaluated using a Fast Repetition Rate fluorometer (FRRf). To determine whether alginate influenced the sensitivity of algal response, studies were also conducted in a static test system (without renewal of test solutions) using both free cells and immobilised cells with initial chlorine added to achieve a similar range of concentrations as those used in the flow-through study. Within the first hour of the exposure period there was an indication that, for both species, the free algal cells in the static system were more sensitive to exposure to chlorinated seawater than were alginate-immobilised cells in the flow through system. Immobilised cells in a static system with a single addition of chlorine were also less sensitive to chlorination than free algal cells. However, for periods of 24 h or more due to decay of TRO in the static system the exposure of immobilised algae in the flow through system had a greater impact and hence lower effect concentrations. For the flow-through studies Achnanthes spp. was the most sensitive after 72 h exposure with a potential no effect concentration EC 10 value of 0.02 mg l -1 as Cl 2 equivalents expressed as total residual oxidants (TRO) compared 0.04 mg l -1 TRO for N. pelliculosa. Immobilisation of algal cells in alginate was found to be an effective means of determining the impact of chlorination and is likely to be effective for other non-persistent substances. Based on the data produced, the extent and significance of ecological effects of chlorination upon algal species typical of microphytobenthos are likely to be limited providing discharges comply with a maximum allowable concentration of 0.01 mg l -1 TRO at the edge of an agreed mixing zone., (Copyright © 2018. Published by Elsevier B.V.)

Chemical pollution of the marine environment from anthropogenic sources is a global concern due to the potential for long term effects on the ecosystem. Chemical monitoring schemes can detect harmful substances in water, sediment or biota. However, the presence of specific determinants gives no information on how individual species or the ecosystem are impacted. Biological effects techniques are therefore used in environmental monitoring schemes to provide a clearer picture of whether the chemicals present are causing deleterious effects on the species sampled, or whether organisms have been exposed to certain classes of organic contaminants that they may be able to metabolise. Using these techniques, we can provide an assessment of the health of our marine environment (Thain et al., 2008)., (Crown Copyright © 2018. Published by Elsevier Ltd. All rights reserved.)

The European XFEL is a free-electron laser (FEL) with a superconducting linear accelerator and three beamlines (SASE1, SASE2, and SASE3) covering the energy range from 250 eV to 24 keV. The SASE3 beamline is dedicated to the soft x-ray range (0.25-3 keV) and is designed to operate in both monochromatic and non-monochromatic mode. A variable line spacing - plane grating (VLS-PG) monochromator is placed along the beam transport system for the monochromatic mode. The VLS parameters of the grating profile are challenging from a manufacturing and measuring perspective, especially at the desired length of 530 mm. A shorter grating of 150 mm has been procured to allow early operation of the facility. We describe the characterization method that was used to assess the VLS parameters of the grating using Fizeau interferometry. The method is intrinsically absolute and limited only by the quality of the test grating and the noise level. Further measurements using a white-light-interferometry profilometer are also reported. We discuss the possibility of extending the method to the future 530 mm long grating.

Ion irradiation is a widely employed tool to fabricate diamond micro- and nano-structures for applications in integrated photonics and quantum optics. In this context, it is essential to accurately assess the effect of ion-induced damage on the variation of the refractive index of the material, both to control the side effects in the fabrication process and possibly finely tune such variations. Several partially contradictory accounts have been provided on the effect of the ion irradiation on the refractive index of single crystal diamond. These discrepancies may be attributable to the fact that in all cases the ions are implanted in the bulk of the material, thus inducing a series of concurrent effects (volume expansion, stress, doping, etc.). Here we report the systematic characterization of the refractive index variations occurring in a 38 µm thin artificial diamond sample upon irradiation with high-energy (3 MeV and 5 MeV) protons. In this configuration the ions are fully transmitted through the sample, while inducing an almost uniform damage profile with depth. Therefore, our findings conclusively identify and accurately quantify the change in the material polarizability as a function of ion beam damage as the primary cause for the modification of its refractive index.

A precise spectral characterization of every single pulse is required in many x-ray free-electron laser (XFEL) experiments due to the fluctuating spectral content of self-amplified spontaneous emission (SASE) beams. Bent single-crystal spectrometers can provide sufficient spectral resolution to resolve the SASE spikes while also covering the full SASE bandwidth. To better withstand the high heat load induced by the 4.5 MHz repetition rate of pulses at the forthcoming European XFEL facility, a spectrometer based on single-crystal diamond has been developed. We report a direct comparison of the diamond spectrometer with its Si counterpart in experiments performed at the Linac Coherent Light Source.

We propose a method to control and to adjust in a closed-loop a bendable x-ray mirror using displacement-measuring devices. For this purpose, the usage of capacitive and interferometric sensors is investigated and compared. We installed the sensors in a bender setup and used them to continuously measure the position and shape of the mirror in the lab. The sensors are vacuum-compatible such that the same concept can also be applied in final conditions. The measurement is used to keep the calibration of the system and to create a closed-loop control compensating for external influences: in a demonstration measurement, using a 950 mm long bendable mirror, the mirror sagitta is kept stable inside a range of 10 nm Peak-To-Valley (P-V).

One of the classical devices used to tune a mirror on an X-ray optical setup is a mechanical bender. This is often designed in such a way that the mirror is held with clamps on both ends; a motor is then used to put a torque on the clamps, inducing a cylindrical shape of the mirror surface. A mechanical bender with this design was recently characterized, to bend a 950 mm-long mirror up to a radius of curvature of 10 km. The characterization was performed using a large-aperture Fizeau interferometer with an angled incidence setup. Some particular and critical effects were investigated, such as calibration, hysteresis, twisting and long-term stability.

The European XFEL (X-ray Free Electron Laser) is a large facility under construction in Hamburg, Germany. It will provide a transversally fully coherent x-ray radiation with outstanding characteristics: high repetition rate (up to 2700 pulses with a 0.6 ms long pulse train at 10 Hz), short wavelength (down to 0.05 nm), short pulse (in the femtoseconds scale), and high average brilliance (1.6 ⋅ 10(25) (photons s(-1) mm(-2) mrad(-2))/0.1% bandwidth). The beam has very high pulse energy; therefore, it has to be spread out on a relatively long mirror (about 1 m). Due to the very short wavelength, the mirrors need to have a high quality surface on their entire length, and this is considered very challenging even with the most advanced polishing methods. In order to measure the mirrors and to characterize their interaction with the mechanical mount, we equipped a metrology laboratory with a large aperture Fizeau interferometer. The system is a classical 100 mm diameter commercial Fizeau, with an additional expander providing a 300 mm diameter beam. Despite the commercial nature of the system, special care has been taken in the polishing of the reference flats and in the expander quality. We report the first commissioning of the instrument, its calibration, and performance characterization, together with some preliminary results with the measurement of a 950 mm silicon substrate. The intended application is to characterize the final XFEL mirrors with nanometer accuracy.

A full-scale piezo bendable mirror built as a prototype for an offset mirror at the European XFEL is characterized. The piezo ceramic elements are glued onto the mirror substrate, side-face on with respect to the reflecting surface. Using a nanometre optical component measuring machine and a large-aperture Fizeau interferometer, the mirror profile and influence functions were characterized, and further analysis was made to investigate the junction effect, hysteresis, twisting and reproducibility.

A method to provide absolute planarity measurements through an interferometric oblique incidence setup and an iterative algorithm is presented. With only three measurements, the calibration of absolute planarity is achieved in a fast and effective manner. Demonstration with synthetic data is provided, and the possible application to very long flat mirrors is pointed out.

An interferometric method to monitor the thinning process of vertical soap films from a water solution of surfactant materials is reported. Raw data maps of optical path difference introduced by the film are obtained by conventional phase shift interferometry. Off-line re-processing of such raw data taking into account the layered structure of soap films leads to an accurate measurement of the geometrical thickness. As an example of data acquisition and processing, the measuring chain is demonstrated on perfluoropolyether surfactants; the section profile of vertical films is monitored from drawing to black film state, and quantitative data on the dynamics of the thinning process are presented. The interferometric method proves effective to the task, and lends itself to further investigate the physical properties of soap films.