SCIENCE & FRONTIER RESEARCH · SWITZERLAND
Paul Scherrer Institute
Giant machines that make the invisible visible
Original schematic illustration · created for the Atlas — stylised technical drawing, not a photograph.
01 In brief
The Paul Scherrer Institute (PSI) in Villigen, on the Aare river between Zurich and Basel, is one of Switzerland's largest research centres for natural and engineering sciences. Formed in 1988 through a merger of earlier federal research institutes, PSI specializes in two things: matter and energy — how materials are built at the atomic scale, and how energy can be produced, stored and used more efficiently.
What makes PSI unusual is its fleet of "large research facilities": machines the size of buildings that produce intense beams of X-rays, neutrons and muons. Researchers from across Switzerland and around the world travel to Villigen to use them — the Swiss Light Source synchrotron, the SINQ continuous neutron source (in operation since 1996), the SμS muon source, and SwissFEL, a 740-metre X-ray free-electron laser.
02 Why it's interesting
- 01 It is a "user factory" for experiments: thousands of guest researchers come to Villigen every year to probe materials with beams that cannot be produced in any ordinary laboratory.
- 02 The same instruments serve wildly different questions — protein structures for drug design, battery electrodes, turbine materials, magnetic data storage, even archaeological artefacts — because X-rays and neutrons see inside matter without destroying it.
- 03 PSI connects fundamental research to Switzerland's energy transition, running dedicated programmes on energy systems and the sustainable use of resources.
- 04 The Swiss Light Source has recently undergone a major "SLS 2.0" upgrade to sharpen its beams further — a routine practice here of continually rebuilding world-class instruments.
03 How it works
PSI's facilities all follow the same principle: accelerate particles to near light speed or smash them into targets, and use the resulting radiation as a probe.
In the Swiss Light Source, electrons circulate in a 2.4-GeV storage ring; as bending magnets and undulators wobble the electron beam, it emits intensely bright X-rays. Experiment stations around the ring use that light for diffraction, imaging and spectroscopy — revealing atomic structures and chemical states.
SINQ works differently: a powerful proton beam strikes a heavy-metal target, knocking neutrons loose. Because neutrons carry no electric charge and have a magnetic moment, they penetrate deep into materials and are uniquely sensitive to light elements and magnetism.
SwissFEL pushes the frontier further: a 740-metre linear accelerator drives electrons through undulator magnets until they emit laser-like X-ray flashes just femtoseconds long — fast enough to film chemical reactions as they happen.
| SLS storage-ring energy | 2.4 GeV (third-generation synchrotron) |
|---|---|
| SwissFEL length | 740 m · femtosecond X-ray pulses |
| SINQ neutron source | Continuous source, operating since 1996 |
| Founded | 1988 (merger of EIR and SIN) |
| Governance | Part of the ETH Domain |
Facility figures per PSI's official facility pages.
04 The organisation behind it
PSI is a federal institute within the ETH Domain, alongside ETH Zurich, EPFL, Empa, Eawag and WSL. It is publicly funded, with its large facilities made available to the national and international research community through a competitive proposal process.
05 In the real world
Research at PSI feeds directly into applied fields: structural biology supports pharmaceutical development; neutron and X-ray imaging helps develop better batteries, catalysts and fuel cells; and PSI's own energy-research programmes analyse pathways for a sustainable Swiss energy system. Its instruments also serve industry directly, from materials testing for power-plant turbines to the study of ancient manuscripts.
06 Can you visit?
Yes — PSI runs a visitor programme with guided tours of its campus and large facilities. Tours generally require registration in advance and are offered for groups and individual visitors on scheduled dates.
See the institute's official website for the current programme, as technical operation of the facilities shapes what can be visited.