Dear colleagues,

Exciting times lie ahead, with PSI’s new top-priority project IMPACT picking up speed quickly! 

IMPACT stands for “Isotope and Muon Production using Advanced Cyclotron and Target technologies” and in December 2024, the Swiss parliament approved the funding and realization of the project as part of the 2025–2028 budget for the ETH domain. The High Intensity Muon Beams (HIMB) should come into operation in 2028, and the isotope production facility TATTOOS in 2030.

HIMB will replace the present HIPA target station M with a new target station H, with a four-times longer, slanted target. New large-acceptance beamlines muH2 and muH3 will replace piM1 and piM3, respectively. While the existing downstream part of piM3 will continue to be used, piM1 will disappear completely. The new muH2 and muH3 beams are optimized for the highest collection and transport efficiencies of low-momentum muons, with muH2 designed to deliver an unprecedented rate of 10¹⁰/s surface muons to experiments.

The Conceptual Design Report laid out a rough timeline. Now the planning is getting more concrete and the entire IMPACT team is working in an extremely focused manner to deliver the project. Currently, design and acquisition of long-lead items are the highest priority.

Following a project retreat in autumn 2025, the IMPACT Steering Committee will decide in December 2025 on the consolidated project timeline and the long shutdown of HIPA required for the disassembly and rebuilding of the target station. We presently expect that the HIPA accelerators — and therefore CHRISP, SμS and SINQ — will be in shutdown from just before Christmas 2026 until July 2028. In addition, the following beamlines in the WEHA experimental hall will be closed already earlier: piM1 (scheduled for 10 October 2026, CHRISP), piM3 (23 November 2026, SμS instruments GPS and FLAME) and muE4 (16 November 2026, SμS instrument LEM). 

We will of course inform you again at the beginning of 2026 to confirm the final shutdown schedule. 

Klaus Kirch
on behalf of the Laboratory for Particle Physics, PSI Center for Neutron and Muon Sciences CNM

An overview of all proposal submission deadlines of the PSI facilities can be found here.

Vacuum ultraviolet (VUV) spectroscopy provides a window into valence transitions and molecular bonding, but measuring liquid samples has been severely limited by the need for transmission windows that restrict the accessible energy range below 10.5 eV. Now, researchers from PSI, in collaboration with colleagues from SLAC, have developed a windowless approach using gas-squeezed liquid jets to create ultrathin water sheets down to 20 nanometers in thickness. At the VUV beamline of SLS, they recorded the first VUV absorption spectrum of liquid water extending up to 13 eV. The team discovered that their water sheets — at the verge of the supercooled regime (0 ± 3°C) — exhibit a blue-shifted absorption peak at 8.52 eV compared to values reported in the literature, reflecting the weakening of the hydrogen-bond network due to reduced thermal energy. However, they found that thin-film interference effects significantly distort the measured spectra when sample thickness approaches the probe wavelength, requiring careful Fresnel propagation modelling to extract accurate absorption coefficients. The newly established capabilities open up fresh possibilities for studying solvation and interface effects in the previously inaccessible VUV energy range without window limitations.

J. Knurr et al., Physical Chemistry Chemical Physics 27, 6457 (2025)
DOI: 10.1039/D4CP04619F

The topological Hall effect (THE) arises from non-coplanar magnetic structures with finite scalar spin chirality, which deflect conduction electrons through emergent magnetic fields. However, for magnetic structures with zero scalar spin chirality, the emergence of a finite topological Hall signal presents a conceptual challenge. Now, an international team of researchers reports that the itinerant helimagnet Fe₃Ga₄ exhibits a substantial THE at and above room temperature through a fluctuation-driven mechanism. Using neutron scattering experiments at SINQ, ILL and ISIS, they identified a helical spiral phase that transforms into a transverse conical state under applied magnetic field. Despite this conical state having zero scalar spin chirality by symmetry, directional breaking of time-reversal symmetry leads to an unbalanced population of chiral magnons, generating dynamic scalar spin chirality. The resulting THE magnitude is comparable to materials hosting skyrmion lattices, but in a simpler magnetic structure at higher temperatures. These findings establish an alternative route for generating topological transport phenomena in itinerant magnets, significantly expanding the materials landscape for room-temperature spintronic applications.

P. R. Baral et al., Nature Communications 16, 3898 (2025)
DOI: 10.1038/s41467-025-58933-w

The discovery of superconductivity in La₃Ni₂O_7–δ under pressure has sparked intense interest, particularly as it emerges upon suppression of a competing density-wave order. However, the nature of this density wave remained unclear. Now, researchers from PSI, in collaboration with colleagues from the Ruhr-Universität Bochum, have used muon-spin rotation and relaxation experiments under hydrostatic pressure to reveal that what appeared to be a single density wave transition actually consists of two distinct orders. At ambient pressure, they identified a spin density wave with stripe-type magnetic ordering at 151 K, followed by a separate, likely charge density wave transition at 131 K. Under increasing pressure, the magnetic ordering temperature rises at 2.8 K GPa⁻¹, while the unidentified density wave transition temperature falls dramatically at −26 K GPa⁻¹. Dipole-field calculations confirm the compatibility of the magnetic structure with alternating lines of magnetic moments and non-magnetic stripes. These findings suggest that La₃Ni₂O_7–δ hosts coexisting spin and charge density waves with remarkably different pressure responses, providing crucial insights into the competing phases that have to be suppressed for superconductivity to emerge in this high-temperature superconductor.

R. Khasanov et al., Nature Physics 21, 430 (2025)
DOI: 10.1038/s41567-024-02754-z

Serial femtosecond crystallography (SFX) exploits the ‘diffraction before destruction’ principle, using ultrashort X-ray pulses to capture molecular structures before radiation damage can occur. However, the question remains whether X-ray-induced changes happen during the pulse itself. Researchers from the Diamond Light Source and SwissFEL have now conducted a systematic study measuring XFEL pulse durations in real time during crystallography experiments. Using a wakefield structure at SwissFEL, they directly measured pulse durations ranging from less than 10 fs to more than 50 fs while varying pulse energies from 10 to 100 µJ, creating a comprehensive map of dose rates. Testing two radiation-sensitive proteins — the iron-heme peroxidase DtpAa and disulfide-rich thaumatin — they observed subtle difference-map features consistent with ionization effects, but found no significant changes in refined atomic coordinates or key bond lengths. Even the highly radiation-sensitive Fe(III)–H₂O bond in DtpAa remained stable across all conditions. These findings provide experimental verification that under typical SFX conditions, longer pulses up to 50 fs may be considered reasonable for typical SFX experiments, offering important guidance for optimizing XFEL experiments.

L. J. Williams et al., International Union of Crystallography Journal 12, 358 (2025)
DOI: 10.1107/S2052252525002660

An international team of more than 40 researchers, led by PSI scientists, has measured the charge radius of the helium-3 nucleus with unprecedented accuracy. The challenging experiment was made possible by PSI’s proton accelerator facility, where the team produced muonic helium-3, in which the two electrons of the helium atom are replaced by a muon. In such hydrogen-like light muonic ions, the nuclear radius can be determined with high precision using pulsed laser spectroscopy. By measuring three 2S-2P transitions in the muonic helium-3 ion, the researchers were able to determine the Lamb shift, the 2P fine structure splitting, and the 2S hyperfine splitting. By comparing these measurements with theoretical predictions, they determined a root-mean-square charge radius of the helium-3 nucleus of 1.97007(94) fm. This value is in good agreement with that obtained from elastic electron scattering, but is 15 times more accurate — thereby setting a new standard for theories and further experiments in nuclear and atomic physics. These results also bring the experiments on light muonic atoms to a close, for the time being. Previously, the researchers have measured muonic helium-4 and, a few years ago, the atomic nuclei of muonic hydrogen and deuterium.

K. Schuhmann et al., Science 388, 854 (2025)
DOI: 10.1126/science.adj2610

SLS: Limited call for proposals

The upgrade of the SLS storage ring has to a large extent been completed – after delivering its last photons on 30 September 2023, it underwent a comprehensive upgrade to a diffraction-limited storage ring (DLSR). Some 18 months later, in early April 2025, the new SLS 2.0 was already storing the nominal full 400 mA current with a horizontal emittance approximately 40 times smaller than before the upgrade. In the interim, the first batch of beamlines have started with commissioning.

With this in mind, we are planning a limited user proposal round between 17 November – 19 December 2025 for the Debye, ADDAMS, PXIII, PolLux and superXAS beamlines, before we have again a longer shutdown in Q1/Q2 of 2026 to install the second phase of beamlines. The timeline for this is as follows: 

• Call opens 14 July 2025
• Call closes 20 August 2025, 12:00 noon
• Notification of outcome to users: 30 September 2025
• 17 November – 19 December 2025: beamtime for user operation (might vary according to beamline). Exact dates still to be decided as commissioning will still be ongoing. 

This call will be officially announced in July. Feel free to contact beamline staff of the above-listed beamlines for outstanding questions. 

For more technical details of the overall project please have a look here.

SINQ: New horizontal high-field magnet with ultra-wide beam access

Cryomagnets are essential for research at SINQ, and the number of requests to use them in experiments has increased significantly in recent years. Horizontal magnets are no exception. They are in high demand for use with mapping instruments such as CAMEA and DMC, as well as with small-angle machines such as SANS-I. They are also used on other instruments, including the single-crystal diffractometer ZEBRA and the triple-axis spectrometers TASP and EIGER. Users can currently perform experiments in horizontal magnets with maximum fields of 2 T, 7 T and 11 T, respectively. However, the latter two magnets have very restricted geometries with respect to the incoming and scattered neutron beam. They can only cover 25% and 1% of the available in-plane reciprocal space, respectively, and are therefore mostly suitable for small-angle scattering. By contrast, the 2 T horizontal magnet provides 90% coverage, albeit with rather restrictive magnetic field strength, thereby limiting the accessible parameter space for experiments. 

With funding from the Swiss National Science Foundation and PSI, SINQ will push the development of a new 6 T horizontal magnet. It will enable approximately 80% in-plane coverage, opening up new possibilities for mapping experiments under an applied magnetic field. The project will begin this year, with the new magnet expected to be commissioned in 2027.

SμS: Proposal round II-25

In early June the latest submission deadline for SμS proposals has passed and the user community has again expressed strong request for beamtime at the Swiss Muon Source. The call was open for the instruments FLAME, GPD, GPS, HAL-9500 and LEM, and a total of 97 proposals were submitted asking for 435 days of beamtime.

As in previous rounds, the largest demand was for GPS with 32 new proposals (92 days), followed by FLAME with 24 proposals (81 days) and LEM with 16 proposals (76 days). The proposals are currently under review and the results are expected to be announced in early August.

SwissFEL: Shot-by-shot X-ray absorption spectroscopy for dilute metalloenzymes

An international team including researchers at SwissFEL has developed an approach that enables X-ray absorption spectroscopy (XAS) of dilute metalloenzymes in a shot-by-shot mode. The method addresses the challenges of studying biological samples at XFELs, where shot-to-shot variations and limited energy discrimination have previously restricted XAS measurements for systems with low metal concentrations. The new approach combines a background-suppressed detection scheme using spherically curved LiNbO₃ crystal analyzers with the drop-on-tape sample delivery method. The crystals, bent to a 200 mm radius, operate near backscattering angles to improve detection efficiency while reducing scattering backgrounds. Tests with photosystem II samples (∼0.45 mM Mn) established the feasibility of data collection in 10.5 minutes using 190 μl of sample, compared to 2 hours and 2.8 ml required by conventional methods. The technique has been tested at SwissFEL, LCLS and SACLA, and should enable time-resolved studies of metalloenzyme reactions at XFELs.

CHRISP: A comparative study of target fabrication strategies for microgram muonic atom spectroscopy

Muonic atom X-ray spectroscopy is a technique used to extract absolute nuclear charge radii. Through recent developments by the muX collaboration, it has become possible to measure targets as small as a few micrograms, reducing the amount of required target material by three to four orders of magnitude. However, producing isotopically pure surface targets for this approach has remained a challenge. In a recent publication, the muX collaboration investigated the suitability of several target-fabrication strategies for this approach. This work establishes that ion beams can be used to produce microgram implanted targets, amongst other findings such as comparing and optimizing microgram targets made by molecular plating and drop-on-demand techniques. The ions can be magnetically separated by mass, to produce isotopically pure beams. This is of particular interest in the medium-mass range, where transitions originating from different isotopes strongly overlap. Following this study, a successful measurement was performed using an isotopically pure (>99%) sample of the long-lived radioactive isotope ⁴⁰K, which has a natural abundance of only 0.01%.

Dear colleagues,

Over the past few years, many of you have expressed concerns about the limited catering options available during your research visits to PSI. The situation has indeed been challenging at times, particularly for those working long hours or staying on site overnight. I am therefore pleased to report that your voices have been heard, and thanks to the continued dialogue between users, JUSAP and the PSI User Office, several significant improvements are now in place or on the horizon.

Here are the latest updates:

• Evening meals are back! As of 2 June 2025, evening catering at the Park Innovare restaurant has resumed (Monday to Friday, 17:30–20:00), aligned with the restart of HIPA operations and user programmes at SINQ, SμS and CHRISP. On weekends, the FELFEL service fridge remains available.
• A proper start to your day: Breakfast is now served at the Park Innovare restaurant from 8:00 (Monday to Friday), in cooperation with the PSI Guesthouse.
• Further improvements: Currently options to establish a 24/7 self-service food market in the former Time-Out space at PSI West are being pursued. We will keep you updated as soon as new information becomes available.

We are confident that these improvements will significantly enhance the user experience at PSI. On behalf of JUSAP, I would like to sincerely thank the various stakeholders and the PSI management for the decisions now taken, and all of you for raising your voices and helping to shape these changes.

With best regards,

Yasmine Sassa
On behalf of the JUSAP Committee

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