Switzerland’s largest research institute

An institute built around machines

Most research institutes are built around laboratories. PSI is built around a handful of very large machines: the Swiss Light Source, the X-ray laser SwissFEL, the neutron source SINQ and the muon source SμS, both driven by a proton accelerator. A further facility, CHRISP, serves particle physics. PSI also runs a Center for Proton Therapy with its own medical cyclotron.

PSI describes its research in three main fields: matter and materials, energy and environment, and human health. On its website it groups the work into four research areas: Future Technologies, Energy and Climate, Health Innovation and Fundamentals of Nature.

Size of the institute

At the end of 2025 PSI had about 2,300 employees. In 2025 its total revenues were about CHF 450 million, of which the federal contribution was CHF 300 million, and more than 380 postgraduate students were working on doctoral projects there.

The campus covers 342,000 square metres with around 120 buildings, which PSI compares to 48 football fields. It has its own postal code: 5232 Villigen PSI.

Two institutes in the Aare valley

PSI was formed on 1 January 1988, when the Swiss Federal Institute for Reactor Research (EIR) and the Swiss Institute for Nuclear Research (SIN) merged. In PSI’s words, this made the lower valley of the Aare the location of a major research institute. The new institute was named after the Swiss physicist Paul Scherrer (1890–1969), who taught and did research at ETH Zurich.

The machines arrived over several decades: the proton accelerator has run since 1974, the SINQ neutron source was inaugurated in 1996, the Swiss Light Source in 2001 and SwissFEL in 2016.

Who uses the machines

In 2025 PSI supported about 2,200 scientists at its large facilities, who carried out 789 experiments. Access to the facilities is granted on the basis of scientific merit, together with technical feasibility and safety. PSI does not charge users for beamtime; users cover their own travel and living costs and follow the publication rules of each facility.

PSI belongs to the ETH Domain, the group of federal institutions that also includes ETH Zurich and EPFL. More on this on City & Region.