Dear colleagues,

It is a great pleasure to share with you some developments and advancements at SwissFEL. I wrote my last editorial when SwissFEL just started user operations at the Aramis hard X-ray beamline. Since then, we have successfully put the Athos soft X-ray line into user operations and have continuously added experimental capabilities on an almost annual basis: the Maloja endstation for atomic, molecular and non-linear X-ray sciences as well as the Furka endstation for condensed-matter and materials sciences at Athos, and the Cristallina-MX endstation for fixed-target protein crystallography at the Aramis branch. 

This autumn, the Cristallina-Q endstation for quantum science will follow with a first call for scattering experiments, completing the current suite of instruments. 

Concurrently, we have continuously increased the available user beamtime and number of experiments performed per semester. The hard work and dedication of our staff has often resulted in best-in-class performance and has firmly established SwissFEL on the international landscape. Last but not least, the number of publications shows a healthy growth, reflecting the many internal R&D efforts and a very successful user programme alike. 

But we are not resting on these achievements. A project is underway to fill the currently last remaining experimental space at SwissFEL with the Diavolezza instrument to expand our growing attosecond capabilities. Looking further into the future, we are exploring the science opportunities for a third Porthos undulator line. Together with the Swiss Society for Photon Sciences we are working on an updated roadmap for both our X-ray facilities.

I hope with this short summary I can convey the excitement at SwissFEL. If you have not yet considered SwissFEL for your research, I encourage you to do so and get in touch with us to discuss scientific applications and opportunities. 

We are looking forward to hearing from you!

Christoph Bostedt
On behalf of SwissFEL, PSI Center for Photon Science

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.

Magnetic tapes have almost completely disappeared from our lives and now only enjoy a nostalgic niche existence. However, significant quantities of these analogue magnetic media are still stored in the archives of sound studios, radio and TV stations, museums, and private collections worldwide. Digitising these tapes is an ongoing challenge as well as a race against time, as the tapes degrade and eventually become unplayable. A team at SLS are developing a method to non-destructively digitise degraded audio tapes in the highest quality using X-ray light. To achieve this goal, they have been collaborating with the Swiss National Sound Archives, which have produced custom-made reference recordings and provided audio-engineering know-how. Now a partnership with the Montreux Jazz Digital Project will help to further develop and test the method — and might rescue a unique concert recording of legendary blues guitarist B.B. King that can no longer be directly played back using conventional methods.

Dirac fermions are typically associated with electronic states in materials such as graphene and topological insulators. However, it has been predicted that Dirac fermions can also emerge in quantum spin liquids, without a charge degree of freedom. Now, a team led by researchers from the Chinese Academy of Sciences in Beijing provides spectral evidence that such spin excitations exist in the kagome antiferromagnet YCu₃(OD)₆Br₂[Br_0.33(OD)_0.67]. In neutron scattering experiments performed on the AMATERAS spectrometer at J-PARC (Japan) and the CAMEA spectrometer at SINQ, the researchers found conical spin excitations with a spin continuum inside, which is consistent with the convolution of two Dirac spinons. Some aspects remain to explored further, however. In particular, the locations of the conical spin excitations are not as expected from theory, pointing to a yet-to-be-discovered origin of the Dirac spinons.

Z. Zeng et al., Nature Physics, 9 May 2024 (online)
DOI: 10.1038/s41567-024-02495-z

Superconducting radio-frequency (SRF) components are central to a wide range of applications. Traditionally they have been used in high-power particle accelerators, but more recently also in fields such as quantum technology. An important method for characterising SRF materials is muon spin rotation (μSR), which has been used since 2010 at TRIUMF in Canada and at SµS to measure material parameters with depth resolution down to the nanometre range. Researchers from TRIUMF and PSI have now partnered up to survey the progress made so far and look ahead to future directions. They review both μSR and the related technique of beta-detected nuclear magnetic resonance (β-NMR). In doing so, the authors provide a broad overview of the techniques and dedicated spectrometers that have been developed for μSR and β-NMR experiments and discuss key results — and how they offer unique possibilities, for example in the study of inhomogeneous materials such as doped niobium and heterostructures.

T. Junginger et al., Frontiers in Electronic Materials 4, 1346235 (2024)
DOI: 10.3389/femat.2024.1346235

Terahertz laser pulses are a powerful tool for manipulating the properties of quantum materials through tailored modifications of their crystal structure. Light-induced ferroelectricity in SrTiO₃ is a remarkable demonstration of such physics. Under mid-infrared illumination, this material transforms into a state of permanently ordered electric dipoles, which are absent from its equilibrium phase diagram. In order to identify the intrinsic interactions relevant for the creation of this state, an international team of researchers performed an experiment at the Bernina beamline of the SwissFEL in which the main new insight was obtained not by detecting the positions of the atoms, but by measuring the fluctuations around these atomic positions. They find evidence that these fluctuations are reduced in optically driven SrTiO₃, which might explain why the dipolar structure is more ordered than in equilibrium and why a ferroelectric state could be induced.

M. Fechner et al., Nature Materials 23, 363 (2024)
DOI: 10.1038/s41563-023-01791-y

The muEDM experiment at CHRISP aims to provide the most sensitive measurement of the electric dipole moment (EDM) of the muon. To achieve such unprecedented sensitivity, scientists from across Europe are developing a prototype experiment using the so-called frozen-spin technique, in which a magnetic field is meticulously aligned with a perpendicular electric field so that the spin orientation of the muon always follows its momentum. This will increase the sensitivity to the muon EDM by about three orders of magnitude compared to the best result from the muon g-2 experiment at Brookhaven National Lab. Working towards this goal, the muEDM collaboration has identified systematic effects that could mimic an EDM signal if E- and B-fields are not perfectly aligned, adjusted or stable over time. While most of the effects cancel out upon reversal of the magnetic field, some residual effects remain, and these define the specifications for the uniformity, stability and orientation of the fields — which are challenging but achievable.

G. Cavoto et al, European Physical Journal C 84, 262 (2024)
DOI: 10.1140/epjc/s10052-024-12604-0

SLS: What the SLS 2.0 upgrade will mean for experiments

Tighter beams, brighter light and an extended range of photon energies open up new experimental possibilities to be explored at the new SLS 2.0 synchrotron. In a technical report published in Synchrotron Radiation News, SLS 2.0 Project Leader Hans Braun and Project Leader Photonics Phil Willmott delve into the details. We also invite you to take a look at recent progress on the construction site in our latest video update, which shows the reassembly of the first of twelve arcs that will make up the 288-metre-long storage ring of SLS 2.0.

SINQ: Systematic approach to assess neutron-imaging scintillators

Neutron imaging is well established as a powerful modality for a wide range of applications that require penetration through thick dense samples and sensitivity to light elements. As the neutrons cannot be detected directly, scintillator screens are typically used to convert them into charged particles and these into visible light. However, how best to assess the overall efficiency of these screens for neutron-imaging applications, taking into account all aspects of the detection system, has remained an open problem. PSI researchers have now developed a systematic approach to evaluating the characteristics of scintillator screens, carefully factoring in all sources of noise. This method should provide a solid basis for scintillator selection and optimization in a given imaging setup.

SμS: PiM3 spin rotator back to full operation

During the recent shutdown period, the spin rotator in PiM3 underwent complete servicing and was refurbished with new insulators. Initial tests indicate that it can operate again at its full design voltage of up to 600 kV. In regular operation, it will run at 550 kV, allowing for a spin rotation of up to 60 degrees. As a result, 87% of the full muon polarization is now available for transverse-field µSR measurements on GPS and FLAME.

At the recent deadline for the SµS cycle II-24, a total of 105 proposals have been submitted. The instruments GPS (34) and FLAME (33) received most requests for beamtime but all SµS instruments will be again heavily overbooked in this cycle. The beamtime cycle will run from  01 October to 23 December and the results of the proposal evaluation may be expected in early August.

SwissFEL & SLS: Fundamentally different

Large research facilities such as SwissFEL and SLS deliver unimaginable amounts of data, and even more so after the SLS 2.0 upgrade. Artificial intelligence (AI) is helping in a number of ways to make efficient use of these data and unlock the full research potential of the facilities. In a PSI Story, researchers explain how AI has become an integral part of the research toolkit — fundamentally changing the process of how science is conducted.

CHRISP: 12’000 wires to detect a positron

The MEG II experiment searches for the decay of a positive muon into a positron and photon. The cylindrical drift chamber — a two-metre long, single-volume, position-sensitive gaseous detector that is operated with a He/isobutane gas mixture — is part of the innovative positron spectrometer and is designed to ensure a precise measurement of the momentum of the positron. Nearly 12’000 wires are stretched in the longitudinal direction: 1728 sense wires with a diameter of 25 microns pick up the charge as the positron travels through the gas, and around 10’000 cathode wires with a diameter of 40 or 50 microns shape the electrical field into the desired field configuration. The performance of the drift chamber, as determined from the accumulated data from first year of physics data taking, fully comply with the expectations from Monte Carlo simulations, and its high resolution and efficiency represent a milestone in the development of a tracking detector for future collider machines. 

Back to the Newsletter overview