Dear colleagues,

The upgrade of the Swiss Light Source to a diffraction-limited storage ring employing seven-bend achromats, which began in October 2023, is now well advanced. The 15-month dark time is over and the machine-controls group is now busy commissioning the ring. The first psychologically important milestone in this endeavour was to thread the electrons around the entire storage ring for at least one turn. 

This was achieved after just three days, and merely six days later, a single bunch was maintained using the RF source for over ten minutes. Only the deteriorating vacuum of the ring — a known and expected transient issue — caused the stored current to be dumped. Approximately another week later, a 20-mA current was maintained; this should increase steadily through further conditioning of the ring. 

The scientific staff anticipate first light now at their beamlines with bated breath. The first phase of beamlines should begin commissioning at the end of the second quarter of 2025. Depending on progress, invited first pilot users should take beam starting this summer in an extended beamline-commissioning phase that will continue to the end of 2025. Installation of additional new X-ray sources, in part replacing older sources, will take place in the first quarter of 2026. 

Regular operation of the first set of beamlines is planned for the second semester of 2026, with a call for proposals and resumption of the proposal-review process in Spring 2026. The remaining beamlines are expected to follow suit six months later, at which point SLS 2.0 will be in full operation. 

Thanks not only to the new multibend-achromat ring, but also to novel developments in source technologies, we expect improvements in performance at beamlines that will allow experiments with spatial resolutions and speeds that were previously unimaginable. 

More details of the upgrade, the beamline portfolio, and the return of user operation can be found here.  

Philip Willmott, Frithjof Nolting and Hans Braun  
On behalf of the SLS 2.0 project

A call for SLS proposals will be announced towards the end of the SLS 2.0 upgrade project. An overview of all proposal submission deadlines of the PSI facilities can be found here.

Zoom in to the micro- or nanostructure of functional materials, both natural and synthetic, and you’ll find they consist of thousands upon thousands of coherent domains or grains — distinct regions where molecules and atoms are arranged in a repeating pattern. Such local ordering is inextricably linked to the material properties. These domains are often only tens of nanometres in size, and it is their arrangement in three dimensions over extended volumes that determines the properties of the material. Yet until now, techniques to probe the organisation of materials at the nanoscale have largely been limited to two dimensions or are destructive in nature. Now, using X-rays generated by SLS, a collaborative team of researchers from PSI, ETH Zurich, the University of Oxford and the Max Plank Institute for Chemical Physics of Solids has developed an imaging technique to access this information: X-ray linear dichroic orientation tomography (XL-DOT) is a novel quantitative, non-invasive technique that enables an intragranular and intergranular characterization of extended polycrystalline and non-crystalline materials in three dimensions.

A. Apseros et al., Nature 636, 354 (2024)
DOI: 10.1038/s41586-024-08233-y

Spin moiré superlattices (SMSs) have been proposed as a magnetic analogue of crystallographic moiré systems and as a source of electron minibands with vector-field moiré tunability (as opposed to scalar charge modulation) and Berry curvature effects. However, the realization of an SMS in which a large exchange coupling is transmitted between conduction electrons and localized spins has proved to be challenging. In addition, most candidate systems have carrier mean free paths shorter than their spin moiré lattice constant, which inhibits miniband formation. Now, an international team led by researchers from the Massachusetts Institute of Technology (MIT) has established that the layered magnetic semimetal EuAg₄Sb₂ overcomes these challenges. Based on single-crystal small-angle neutron scattering (SANS) data measured at SINQ, they show that the magnetic modulation period and the Fermi surface match. This combination of spin textures and 2D electron sheets may provide a route to a ‘designer renormalization’ of the electronic structure — and potentially to an emergent spin-driven quantum Hall state.

T. Kurumaji et al., Science Advances 11, eadu6686 (2025)
DOI: 10.1126/sciadv.adu6686

Manganese silicide (MnSi) is a prominent quantum material in which strong electron correlations lead to exotic properties. With an ordered magnetic moment m much smaller than the paramagnetic moment and a relatively low magnetic ordering temperature T_c, MnSi has been classified as a weak itinerant magnet. However, while the self-consistent renormalization theory of the spin fluctuations successfully rationalizes the T_c value and the paramagnetic moment, the strong longitudinal fluctuations of the magnetic moment of MnSi associated with the small value of m remain a challenge for theoretical studies. In order to provide experimental benchmarks for first-principles theories, an international team working at SμS has now measured the evolution of the magnetic moment m and the exchange interaction J as a function of hydrostatic pressure in the zero-field helimagnetic phase of MnSi. Their data show that the previously observed suppression of magnetic order at ≈1.5  GPa arises from a collapse of J, rather than from quantum fluctuations reducing the magnetic moment. Beyond providing insight into MnSi, these findings might also help to gain a fuller understanding of its sibling compounds FeGe and MnGe, and more generally underline the importance of accurate studies of crystal structures in this pressure range.

P. Dalmas de Réotier et al., Physical Review Letters 133, 236502 (2024)
DOI: 10.1103/PhysRevLett.133.236502

Time-resolved serial crystallography (TR-SFX) at X-ray free-electron lasers enables the observation of ultrafast photochemical reactions at the atomic level. The technique has provided exciting molecular insights into various biological processes, including light sensing and photochemical energy conversion. However, to achieve sufficient levels of activation within an optically dense crystal, high laser power densities are often used, which has led to an ongoing debate about the extent to which photodamage might compromise interpretation of the results. An international team led by PSI researchers has now compared TR-SFX data collected at laser power densities ranging from 0.04 to 2493 GW/cm² for an early photocycle intermediate of the bacteriorhodopsin light-driven proton pump. Although the effects of high laser power densities on the overall structure were found to be small, in the upper excitation range they observed significant changes in retinal conformation and increased heating of the functionally critical counterion cluster — providing an example of how and when multiphoton absorption in the femtosecond domain can influence later structural intermediates and their biological interpretation.

Q. Bertrand et al., Nature Communications 15, 10278 (2024)
DOI: 10.1038/s41467-024-54422-8

The MONUMENT experiment at CHRISP measures ordinary muon capture (OMC) in isotopes relevant for neutrinoless double-beta decay and nuclear astrophysics. OMC is a process in which the muon of a muonic atom interacts with one of the protons in the nucleus, leading to a transformation into a neutron and a neutrino. This interaction greatly excites the nucleus and alters its charge from Z to Z-1. The process can be exploited to study the nuclear structure of the newly formed Z-1 nucleus in a regime relevant for the neutrinoless double beta decay transition. While normal double-beta decay, which involves the emission of neutrinos, has been observed in various elements, neutrinoless double beta decay has not and is the subject of numerous experiments. Its discovery would provide evidence of lepton number violation, reveal the nature of the neutrinos, and determine their absolute mass, which is currently subject to significant theoretical uncertainties. The OMC studies aim to address and reduce these uncertainties. While the analysis of the muon capture measurements at PSI is ongoing, a new paper now provides an overview of the experimental apparatus built by the MONUMENT collaboration and outlines the steps involved in extracting the pertinent parameters from the experimental data.

G.R. Araujo et al., The European Physical Journal C 84, 1188 (2024)
DOI: 10.1140/epjc/s10052-024-13470-6

CHRISP Users Meeting BVR56

The 2025 edition of the Users Meeting for the CHRISP facility, the 56^th of its kind, took place from 10 to 12 February 2025. The first day was dedicated to closed, in-depth status reviews of the MEG II, Mu3e, CREMA, PIONEER and muEDM experiments. On the second day, the Open CHRISP Users Meeting BVR56 took place. After a short presentation of user statistics, new developments and highlights from PSI, progress reports were presented by all remaining experiments that were not reviewed on the first day. These covered the areas of measurements of the neutron electric dipole moment, the neutron lifetime, muon-catalysed fusion, muon beam compression, free fall of muonium, and measurements of muonic atoms. The presentations sparked stimulating discussions, which continued during the coffee break. The meeting concluded on the third day with the oral feedback and recommendations to the projects by the president of the Research Committee for Particle Physics at the Ring Cyclotron and the presentation of the beam-time allocations.

Together for science with neutrons, muons and X–rays

A strategic partnership between research facilities in the UK and Switzerland has been established by the UK International Science Partnerships Fund (ISPF), which will develop new capabilities for science using neutrons, muons and X–rays.

Together, UK facilities – ISIS Neutron and Muon Source (ISIS) and the Diamond Light Source, located at the Rutherford Appleton Laboratory (RAL) – and PSI will thus create new scientific capabilities to address global challenges. The first full collaboration meeting was held at RAL in November 2024, when 50 scientists and technologists from ISIS, Diamond and PSI facilities, which include SINQ, SµS, SLS and SwissFEL, gathered to discuss their projects and plan future activities.

CHRISP/SμS: IMPACT upgrade approved

The planned IMPACT upgrade of the proton-accelerator facility at PSI will be implemented. Funding for this two-part upgrade has been secured within the framework of the Dispatch on the Promotion of Education, Research, and Innovation (ERI Dispatch) for 2025–2028, which was approved by the Swiss Parliament in mid-December 2024. The budget includes 50 million Swiss francs through which the ETH Council will co-finance the IMPACT project from central funds. IMPACT is a joint project of PSI, the University of Zurich, and the University Hospital of Zurich. It comprises two major upgrades to PSI’s research facilities: First, under the name HIMB, two beamlines for experiments with muons will be significantly improved. HIMB will increase the number of muons available for research purposes, for example in physics and materials science, by a factor of 100. Second, a new facility called TATTOOS will be built for the production of important radionuclides. These radionuclides are essential components of radiopharmaceuticals used in both the diagnosis and treatment of cancer. 

SLS: Sample-position tracking using computer vision algorithms

Soft X-ray spectroscopy is an important technique for measuring the fundamental properties of materials. However, many experimental setups are limited when it comes to measuring samples in the sub-millimetre range. Position drifts on the order of hundreds of micrometres during thermal stabilization of the system can persist for hours of expensive beam time. To compensate for these drifts, sample tracking and feedback systems are needed, but many existing solutions cannot be applied in complex sample environments. Researchers at PSI and the Zurich University of Applied Sciences have now developed a tracking system based on a computer vision algorithm that automatically tracks the sample position. Using the setup, the overlap between consecutive X-ray absorption spectra was improved by a factor of ten for samples with a vertical size down to 70 µm. The system can be used in a variety of experimental stations where optical access is available but sample access by other means is restricted.

SINQ: Operando neutron characterization during 3D printing

Researchers from PSI, EPFL and the University of Patras have developed a new laser powder bed fusion device to explore metal 3D printing processes in real time using neutrons. It can be installed at different SINQ beamlines. The device is smaller than standard industrial printers but allows similar printing while letting neutrons pass through the materials. With the new setup, it is possible to study the evolution of the structure and properties of metals during printing, which is difficult to achieve with other methods such as X-rays. Initial studies have demonstrated the potential to monitor thermal strain and defects in real time. In addition, the device enables temperature and phase mapping during multi-material printing, such as combining stainless steel and copper alloys. Using a special neutron filter, temperature profiles of the material layers are created as they are printed. These demonstrations establish the potential of the new device to improve 3D printing techniques and material quality for advanced applications.

SwissFEL: Neat, precise and brighter than ever

The pulses produced by X-ray free-electron lasers (XFELs) are noisy in time and frequency, due to the way the light is generated in the self-amplified spontaneous emission (SASE) process. This spectral randomness can be a limitation for experiments that require ultra-high spectral control to follow electron and structural dynamics. Researchers at SwissFEL have now found a way to make the light neat and tidy. By inserting magnetic chicanes to control the timing of the electron beam between undulator modules at the Athos beamline, they achieved two major breakthroughs. First, they created tuneable frequency combs, where the number of spectral lines and their spacing can be varied. Second, they collapsed the frequency combs into a single, ultra-bright ‘tooth’ — a single spectral line with a bandwidth about a third of that of a normal XFEL pulse. Each of these advances should open up new scientific opportunities with XFELs, from fundamental physics to applied sciences.

The Joint Users Association at PSI (JUSAP) serves as a representative body for users of the large-scale research facilities at PSI. Its primary mission is to act as a crucial liaison between users and PSI management and operational bodies, ensuring effective communication and advocacy for user needs.

The previous term of office for the panel members came to an end in December 2024 and we thank the leaving members Joanna Hoszowska, Annick Froideval, Mathilde Reinle-Schmidt and Mogens Christensen cordially for their strong commitment for the users' needs over the past years.

In January the new candidates for the 2025–2028 period were approved by the PSI user community and the new panel met already once in March to get to know each other and to discuss next steps. 

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