Paul Scherrer Institute

Shorter period undulators typically require a higher on-axis magnetic field in order to achieve a practical deflection parameter, K . Recent simulations and experiments have demonstrated that high-temperature superconducting (HTS) undulators, constructed from staggered-array bulk superconductors, can generate high undulator fields with period length as short as 10 mm. This advanced HTS technology has the potential to significantly enhance the photon energy range of synchrotron radiation light sources and free electron laser facilities. This paper reports on the progress made in developing of a 50-period bulk HTS undulator with period length of 12 mm for Shanghai soft x-ray free electron laser facility. It details the engineering design of the undulator prototype, thermal and mechanical analysis of the HTS variable temperature insert, and the current status of the system.

A schematic of the “Himalayan aerosol factory”. Courtesy of Sole Lätti (https://kuvittajat.fi/).

The spiral spin liquid (SSL) is a highly degenerate state characterized by a continuous contour or surface in reciprocal space spanned by a spiral propagation vector. Although the SSL state has been predicted in a number of various theoretical models, very few materials are so far experimentally identified to host such a state. Via combined single-crystal wide-angle and small-angle neutron scattering, we report observation of the SSL in the quasi-two-dimensional delafossite-like AgCrSe2. We show that it is a very close realization of the ideal Heisenberg J1–J2–J3 frustrated model on the triangular lattice. By supplementing our experimental results with microscopic spin-dynamics simulations, we demonstrate how such exotic magnetic states are driven by thermal fluctuations and exchange frustration.

In modern nuclear data evaluations, nuclear reactions and statistical methods cannot be separated. Whereas the first one is continuously improved for many decades, the second one is now benefiting from large computer power. Ahead of its time, our colleague Eric Bauge had understood the advantage of linking them together. He developed modern Bayesian methods, and helped many of us to move in this direction. This short paper will present two examples of the work that we did together, following his vision: the application of BFMC, and the evidence of correlation between nubar, chi and fission cross section. Finally, he was not only a bridge builder, he was also able to jump from fundamental physics to very applied aspects, making him a frontier crosser.

Age‐related changes in human dermal fibroblasts (HDFs) contribute to impaired wound healing and skin aging. While these changes result in altered mechanotransduction, the epigenetic basis of rejuvenating aging cells remains a significant challenge. This study investigates the effects of compressive forces on nuclear mechanotransduction and epigenetic rejuvenation in aged HDFs. Using a compressive force application model, the activation of HDFs through alpha‐smooth muscle actin (ɑ‐SMA) is demonstrated. Sustained compressive forces induce significant epigenetic modifications, including chromatin remodeling and altered histone methylation patterns. These epigenetic changes correlate with enhanced cellular migration and rejuvenation. Small‐scale drug screening identifies the extracellular signal‐regulated kinase (ERK) signaling pathway as a key mediator of compression‐induced epigenetic activation. Furthermore, implanting aged cell spheroids into an aged skin model and subjecting the tissue to compressive forces resulted in increased collagen I protein levels. Collectively, these findings demonstrate that applying compressive force to aged fibroblasts activates global epigenetic changes through the ERK signaling pathway, ultimately rejuvenating cellular functions with potential applications for wound healing and skin tissue regeneration.

Purpose: To present results from the trial radiotherapy quality assurance (RTQA) programme of the centres involved in the randomised phase-III PROton versus photon Therapy for esophageal Cancer – a Trimodality strategy (PROTECT)-trial, investigating the clinical effect of proton therapy (PT) vs. photon therapy (XT) for patients with oesophageal cancer. Materials and methods: The pre-trial RTQA programme consists of benchmark target and organ at risk (OAR) delineations as well as treatment planning cases, a facility questionnaire and beam output audits. Continuous on-trial RTQA with individual case review (ICR) of the first two patients and every fifth patient at each participating site is performed. Patient-specific QA is mandatory for all patients. On-site visits are scheduled after the inclusion of the first two patients at two associated PT and XT sites. Workshops are arranged annually for all PROTECT participants. Results: Fifteen PT/XT sites are enrolled in the trial RTQA programme. Of these, eight PT/XT sites have completed the entire pre-trial RTQA programme. Three sites are actively including patients in the trial. On-trial ICR was performed for 22 patients. For the delineation of targets and OARs, six major and 11 minor variations were reported, and for six patients, there were no remarks. One major and four minor variations were reported for the treatment plans. Three site visits and two annual workshops were completed. Interpretation: A comprehensive RTQA programme was implemented for the PROTECT phase III trial. All centres adhered to guidelines for pre-trial QA. For on-trial QA, major variations were primarily seen for target delineations (< 30%), and no treatment plans required re-optimisation.

Objective. Fast computation of daily reoptimization is key for an efficient online adaptive proton therapy workflow. Various approaches aim to expedite this process, often compromising daily dose. This study compares Massachusetts General Hospital’s (MGH’s) online dose reoptimization approach, Paul Scherrer Institute’s (PSI’s) online replanning workflow and a full reoptimization adaptive workflow for head and neck cancer (H&N) patients. Approach. Ten H&N patients (PSI:5, MGH:5) with daily cone beam computed tomographys (CBCTs) were included. Synthetic CTs were created by deforming the planning CT to each CBCT. Targets and organs at risk (OARs) were deformed on daily images. Three adaptive approaches were investigated: (i) an online dose reoptimization approach modifying the fluence of a subset of beamlets, (ii) full reoptimization adaptive workflow modifying the fluence of all beamlets, and (iii) a full online replanning approach, allowing the optimizer to modify both fluence and position of all beamlets. Two non-adapted (NA) scenarios were simulated by recalculating the original plan on the daily image using: Monte Carlo for NAMGH and raycasting algorithm for NAPSI. Main results. All adaptive scenarios from both institutions achieved the prescribed daily target dose, with further improvements from online replanning. For all patients, low-dose CTV D98% shows mean daily deviations of −2.2%, −1.1%, and 0.4% for workflows (i), (ii), and (iii), respectively. For the online adaptive scenarios, plan optimization averages 2.2 min for (iii) and 2.4 for (i) while the full dose reoptimization requires 72 min. The OAMGH20% dose reoptimization approach produced results comparable to online replanning for most patients and fractions. However, for one patient, differences up to 11% in low-dose CTV D98% occurred. Significance. Despite significant anatomical changes, all three adaptive approaches ensure target coverage without compromising OAR sparing. Our data suggests 20% dose reoptimization suffices, for most cases, yielding comparable results to online replanning with a marginal time increase due to Monte Carlo. For optimal daily adaptation, a rapid online replanning is preferable.

Actinic patterned mask inspection (APMI) is used to verify the quality of photomasks for EUV lithography by revealing eventual defects in the patterned mask layout. The current approach to APMI, based on conventional imaging, is expensive and challenging to scale to keep up with Moore’s law. Ptychography offers a promising alternative for actinic EUV mask inspection by mitigating the need for expensive optics and providing better scalability compared to direct imaging approaches. However, the adoption of this lensless imaging method in semiconductor fabs is hampered by throughput challenges, which are due to the slow, iterative phase retrieval process and to the time-intensive data collection. In this study, we explore and demonstrate a rapid APMI method by exploiting a deep neural network (DNN) architecture which makes use of the extensive prior information available for photomask samples. Our aim is to achieve high-fidelity image reconstruction and identify defects in a photomask sample by processing only a small subset (less than 5% in this case) of the measured diffraction patterns using a network trained exclusively with synthetic data. We developed our DNN using both synthetic and experimental data, and finally, we tested the DNN with a completely synthetic dataset to ensure a clean split among training and test data and to prove that this approach can be used in a real situation with no external information on the mask defect content. Although the DNN was not able to accurately detect all the defects, we used the DNN prediction as a starting point for conventional ptychography and we demonstrated a significant improvement in reconstruction speed even with respect to the case where ptychography is initiated by an educated guess based on the prior knowledge of the mask layout. We conclude the paper by showing the outcome of a die-to-database inspection of a logic–like EUV mask pattern obtained with our approach.

Many neutron techniques can greatly benefit from enhanced neutron lenses for focusing and imaging. In this work, we revisit the potential of diffractive optics for neutron beams, building on advanced high-resolution nano-lithography techniques developed for the fabrication of X-ray diffractive optics used at synchrotron facilities. We demonstrate state-of-the-art fabrication of nickel and silicon Fresnel zone plates and we report proof-of-concept experiments for full-field neutron microscopy and small angle neutron scattering. The advancement of neutron diffractive optics will open new opportunities for neutron techniques, improving both the efficiency and resolution of existing instruments.

Exposure to anthropogenic atmospheric aerosol is a major health issue, causing several million deaths per year worldwide. The oxidation of aromatic hydrocarbons from traffic and wood combustion is an important anthropogenic source of low-volatility species in secondary organic aerosol, especially in heavily polluted environments. It is not yet established whether the formation of anthropogenic secondary organic aerosol involves mainly rapid autoxidation, slower sequential oxidation steps or a combination of the two. Here we reproduced a typical urban haze in the ‘Cosmics Leaving Outdoor Droplets’ chamber at the European Organization for Nuclear Research and observed the dynamics of aromatic oxidation products during secondary organic aerosol growth on a molecular level to determine mechanisms underlying their production and removal. We demonstrate that sequential oxidation is required for substantial secondary organic aerosol formation. Second-generation oxidation decreases the products’ saturation vapour pressure by several orders of magnitude and increases the aromatic secondary organic aerosol yields from a few percent to a few tens of percent at typical atmospheric concentrations. Through regional modelling, we show that more than 70% of the exposure to anthropogenic organic aerosol in Europe arises from second-generation oxidation.

A critical feature of microtubules is their GTP cap, a stabilizing GTP-tubulin rich region at growing microtubule ends. Microtubules polymerized in the presence of GTP analogs or from GTP hydrolysis-deficient tubulin mutants have been used as GTP-cap mimics for structural and biochemical studies. However, these analogs and mutants generate microtubules with diverse biochemical properties and lattice structures, leaving it unclear what is the most faithful GTP mimic and hence the structure of the GTP cap. Here, we generate a hydrolysis-deficient human tubulin mutant, αE254Q, with the smallest possible modification. We show that αE254Q-microtubules are stable, but still exhibit mild mutation-induced growth abnormalities. However, mixing two GTP hydrolysis-deficient tubulin mutants, αE254Q and αE254N, at an optimized ratio eliminates growth and lattice abnormalities, indicating that these ‘mosaic microtubules’ are faithful GTP cap mimics. Their cryo-electron microscopy structure reveals that longitudinal lattice expansion, but not protofilament twist, is the primary structural feature distinguishing the GTP-tubulin containing cap from the GDP-tubulin containing microtubule shaft. However, alterations in protofilament twist may be transiently needed to allow lattice compaction and GTP hydrolysis. Together, our results provide insights into the structural origin of GTP cap stability, the pathway of GTP hydrolysis and hence microtubule dynamic instability.

The magnetic structure of diamond-like lattice has been studied extensively in terms of the magnetic frustration. Here we report the distortion of stretched diamond lattice of Tb³⁺ (4f⁸) in M–TbTaO4 on application of a magnetic field. We have investigated the structural and magnetic properties of M phase terbium tantalate M–TbTaO4 as a function of temperature and magnetic field using magnetometry and powder neutron diffraction. Sharp λ-shape transitions in d(χT)/dT, dM/dH and specific heat data confirm the previously reported three-dimensional (3D) antiferromagnetic ordering at TN ∼ 2.25 K. On application of a magnetic field the Néel temperature is found to decrease and variable field neutron diffraction experiments below TN at 1.6 K show an increase in both the bond and angle distortion of the stretched diamond lattice with magnetic field, indicating a potential magneto-elastic coupling effect. By combining our magnetometry, heat capacity and neutron diffraction results we generate a magnetic phase diagram for M–TbTaO4 as a function of temperature and field.

The Patrónite vanadium tetrasulfide (VS4) follows a simultaneous cationic and anionic redox (SCAR) mechanism in magnesium batteries, which renders a delocalized electronic structure for fast kinetics and meanwhile enables multielectron reactions for delivering high capacity. In contrast to most research that focuses on the hydrothermal route resulting in VS4 nanoparticles, herein a more industrially relevant synthesis route is targeted, utilizing a solid‐state approach leading to micron‐sized VS4. The obtained 2 × 10 μm VS4 needles show good water/air stability, allowing an environmentally friendly coatings procedure using polyvinylpyrrolidon binder in isopropanol. Electrochemical investigation shows that the micron‐sized VS4 cathode delivers a maximum capacity of 420 mAh g⁻¹ in a tetrakis(hexafluoroisopropyloxy)borate (Mg[B(hfip)4]2)‐based electrolyte, however suffers from fast capacity fading and overcharging. Targeting these issues, a concentrated Mg[B(hfip)4]2 electrolyte in bis(2‐methoxyethyl)ether is applied, which enables stable cycling for 300 cycles at the expense of a reduced capacity. Multimodal characterizations confirm a reversible SCAR mechanism of VS4 during cycling. However, pulverization of the electrode and fragmentation of the VS4 backbones are evident, leading to the leakage of active material into electrolyte and causing capacity decay. To avoid active material loss, crystal engineering or surface protection strategies should be developed toward practical Mg batteries.

Controlling the correlations and electronic reconstruction at the interface of transition metal oxide heterostructures provides a new pathway for tuning their unique physical properties. Here, we investigate the effects of interfacial nonstoichiometry and vertical phase separation on the magnetic properties and proximity-induced magnetism of epitaxial La0.7Sr0.3MnO3 (LSMO)/SrTiO3(001) oxide heterostructures. We also reinvestigate the recently observed inverse hysteresis behavior reported for this system, which we find emanates from the remanent field of the superconducting solenoid and not from antiferromagnetic intra-layer exchange coupling in low coercivity LSMO thin films. Combined atomically resolved electron energy loss spectroscopy, element-specific X-ray magnetic circular dichroism, and interface-sensitive polarized soft X-ray resonant magnetic reflectivity show the formation of a Mn³⁺-enriched interfacial LSMO layer, of a Ti³⁺-derived magnetic interface layer coupled ferromagnetically to La0.7Sr0.3MnO3, together with a small density of O-vacancies at the interface. These results not only advance the understanding of the magnetism and spin structure of correlated oxide interfaces but also hold promise for practical applications, especially in devices where the performance relies on the control and influence of spin polarization currents by the interfacial spin structure.

The generation and dynamics of plasmon-induced hot carriers in gold nanoparticles offer crucial insights into nonequilibrium states for energy applications, yet the underlying mechanisms remain experimentally elusive. Here, we leverage ultrafast X-ray absorption spectroscopy (XAS) to directly capture hot carrier dynamics with sub-50 fs temporal resolution, providing clear evidence of plasmon decay mechanisms. We observe the sequential processes of Landau damping (~25 fs) and hot carrier thermalization (~1.5 ps), identifying hot carrier formation as a significant decay pathway. Energy distribution measurements reveal carriers in non-Fermi-Dirac states persisting beyond 500 fs and observe electron populations exceeding single-photon excitation energy, indicating the role of an Auger heating mechanism alongside traditional impact excitation. These findings deepen the understanding of hot carrier behavior under localized surface plasmon resonance, offering valuable implications for applications in photocatalysis, photovoltaics, and phototherapy. This work establishes a methodological framework for studying hot carrier dynamics, opening avenues for optimizing energy transfer processes in nanoscale plasmonic systems.

Alkali-metal doped polyaromatic hydrocarbons (PAHs) have shown great potential in realizing exotic states of matter such as quantum spin liquids (QSLs). However, it is challenging to obtain new pure-phase candidates and perform experimental identifications accordingly. Here, we report the discovery and characterization of Cs(chrysene˙⁻)(THF)0.5·(THF)0.25 (1, THF = tetrahydrofuran), a pure-phase spin-½ organic magnet composed of triangular-based zig-zag magnetic layers, which give rise to strong spin frustration. Electron paramagnetic resonance and optical analyses show 1 is a Mott insulator. Despite the strong antiferromagnetic coupling, low-temperature specific heat and ac susceptibility demonstrate the absence of both long-range magnetic order and spin-glass phases down to 55 mK. Magnetic specific heat can be fitted to the power law, implying gapless spin excitation. Muon spin relaxation reveals constant spin fluctuation rates, suggesting persistent slow dynamics down to 0.3 K. Our results highlight PAHs as a promising avenue for exploring new QSLs.

Bimetallic heterogeneous catalysts combining group 9 metals (Rh, Ir) or group 10 metals (Ni, Pd, Pt) with Mo on a silica-based support have been synthesized via surface organometallic chemistry and assessed in their catalytic activity for the hydrodeoxygenation (HDO) of alcohols with particular emphasis on the structural evolution of the catalysts and the role of Mo. The investigation was conducted with an air-free approach to isolate any sample alterations exclusively to those caused by the reaction. Structural analysis was performed using a combination of (S)TEM, IR, and XAS. It was found that Ir–Mo/SiO2, Rh–Mo/SiO2, and Pt–Mo/SiO2 display high activity for primary, secondary, and tertiary alcohol deoxygenation, while Pd–Mo/SiO2 selectively catalyses tertiary alcohol deoxygenation. Other combinations as well as the corresponding monometallic materials do not display the same activity. X-ray absorption spectroscopy confirmed metallic states for M (M = Ni, Rh, Pd, Ir, or Pt), while Mo K-edge XANES showed varying amounts of Mo(0), Mo(iv) and Mo(vi) depending on the metal counterpart in fresh materials, and indicated complete conversion of Mo(vi) to lower oxidation states (IV and 0) during the reaction. For Rh, Pd, Ir, and Pt, alloy formation (M–Mo) was identified via M–Mo paths in EXAFS and supported by CO-IR spectroscopy. In contrast to Ir, Rh, and Pt, where some Mo(0) is present at the nanoparticle surface, Pd–Mo forms an alloy but likely retains Mo in the nanoparticle core, as suggested by CO-IR spectroscopy and CO-chemisorption. Reactivity studies suggest that tertiary alcohols primarily undergo dehydration–hydrogenation, evidenced by olefin formation with MoOx/SiO2, as well as Ir/SiO2 and Ir–Mo/SiO2 under inert conditions. In contrast, primary and secondary alcohols follow a different mechanism, correlated with the presence of metallic Mo species on the nanoparticle surface, highlighting their role in C–O bond activation. These findings provide new insights into the structure–activity relationships of Mo-based bimetallic catalysts, underscoring the influence of Mo in different oxidation states and strong substrate dependence on mechanistic pathways.