Paul Scherrer Institute

The Paul Scherrer Institute (PSI) is a multi-disciplinary research institute which belongs to the Swiss Federal Institutes of Technology Domain covering also ETH Zurich and EPFL. It was established in 1988 through the merger of EIR (Eidgenössisches Institut für Reaktorforschung, Federal Institute for Reactor Research, established in 1960) and SIN (Schweizerisches Institut für Nuklearphysik, Swiss Institute for Nuclear Physics, established in 1968). It is based in Villigen and Würenlingen.

The PSI is a multi-disciplinary research centre for the natural sciences and technology. In national and international collaboration with universities, other research institutes and industry, PSI is active in solid-state physics, materials sciences, elementary particle physics, life sciences, nuclear and non-nuclear energy research, and energy-related ecology.

It is the largest Swiss national research institute with about 1,900 members of staff as of 2014, and is the only one of its kind in Switzerland.[1]

PSI is a User Laboratory, offering access to its facilities to researchers affiliated to many different institutions, and it runs several particle accelerators. The 590 MeV cyclotron, with its 72 MeV companion pre-accelerator, is one of them. As of 2011, it delivers a proton beam of up to 2.2 mA, which is the world record for such proton cyclotrons. It drives the spallation neutron source complex. The Swiss Light Source (SLS), built in 2001, is a synchrotron light source with a 2.4 GeV electron storage ring. It is one of the world's best with respect to electron beam brilliance and stability. An X-ray free-electron laser called SwissFEL is currently under construction and is slated to begin operation in 2016.[2]

The proton accelerators are also used for the proton therapy program.

Research fields

Proton accelerators


Type: Cyclotron
Magnet: H-Form
Magnet mass: 500 t
Poll-plates radius: 125 cm
Poll=plates Distance: 20 cm
Vacuum chamber volume: 20 m3
Energy: Variable

Injector 1 is a variable energy cyclotron built by the Dutch company Philips Gloeilampen-Fabrieken. Its one-piece magnet has an azimuthally varying magnetic field for vertical focusing even at relativistic energies. The beam energy goes up to 72 MeV for protons and 120 MeV Z2/A for ions with charge Z and mass number A. Equipped with several ion sources, Injector 1 offers a wide variety of beams ranging from protons and deuterons to light and heavy ions. Polarized beams of protons and deuterons are also available. In 1994 an ECR ion source was installed to extend its ability to accelerate heavy ions. This machine has been decommissioned on 1 December 2010.


Type: Isochronous-Cyclotron
Magnets: 4
Total Magnet mass: 760 t
Accelerating elements: 4 Resonators (50 MHz)
Energy: 72 MeV

The Injector 2 cyclotron has been built to replace the multiparticle variable energy Injector 1. It provides high intensity, high quality beams of 72 MeV protons to be injected into the 590 MeV Ring cyclotron.

The Injector 2 is itself a ring cyclotron, but with 4 sectormagnets and with an extremely low injection energy of 870 keV. The 870 keV proton beam is achieved by extracting protons from an ion source with 60 kV and additional acceleration of the particles by means of a Cockcroft-Walton type accelerator operated at 810 kV.

It was put in operation in 1984.


PSI Ring Cyclotron
Type: Isochronous-Cyclotron
Magnets: 8
Total Magnet mass: 2000 t
Accelerating elements: 4 (5) Cavities (50 MHz)
Kinetic Energy:[3] 590 MeV

The Ring Cyclotron is a separated sector cyclotron with a fixed beam energy of 590 MeV, built by PSI and commissioned in 1974. The 72 MeV beam from either one of two injector cyclotron enters from the back of the cyclotron, is injected into an orbit in the center of the Ring, accelerated over about 186 revolutions and extracted at the full energy.

The design is based on criteria that allow operation at very high beam intensities: an open structure of four large and powerful RF-cavities providing a high acceleration voltage, and a flat-top cavity operating at the third harmonic of the accelerating RF-voltage. The resulting strong, phase-independent energy gain per revolution gives good turn separation and hence beam extraction with low beam losses. This is a mandatory condition for high current operation in a cyclotron. Presently, a continuous beam current of 2.2 mA at 590 MeV can be extracted from the ring cyclotron. This corresponds to a beam power of approximately 1.3 MW turning the PSI-proton facility into the world's most powerful accelerator complex at the moment.

Spallation Neutron Source (SINQ)

Neutron scattering is one of the most effective ways to obtain information on both the structure and the dynamics of condensed matter. A wide scope of problems, ranging from fundamental to solid state physics and chemistry, and from materials science to biology, medicine and environmental science, can be investigated with neutrons. Aside from the scattering techniques, non-diffractive methods like imaging techniques can also be applied with increasing relevance for industrial applications.

The spallation neutron source SINQ is a continuous source – the first of its kind in the world – with a flux of about 1014 n/cm2/s. Beside thermal neutrons, a cold moderator of liquid deuterium (cold source) slows neutrons down and shifts their spectrum to lower energies. These neutrons have proved to be particularly valuable in materials research and in the investigation of biological substances. SINQ is a user facility. Interested groups can apply for beamtime on the various instruments by using the SINQ proposal system.

Spallation Ultracold Neutron Source (UCN)

Neutrons from the spallation target are brought to thermal energies by means of a heavy water. Some of the neutrons are further cooled down to kinetic energies below 300 neV by means of a solid deuterium moderator.[4][5]

These ultra cold neutrons are used by the nEDM experiment[6] to probe the Neutron electric dipole moment at scales below the current upper limit (|dn| < 2.9×10−26e·cm[7])

Swiss Light Source (SLS)

Main article: Swiss Light Source
Panorama of the Swiss Light Source

Swiss Muon Source (SμS)

Thanks to the high proton current (2200 μA), the Swiss Muon Source is the world's most intense continuous beam muon source today.[8] One of the main applications of these intense muon beams is Muon spin spectroscopy.

Proton Therapy Programme

Since 1984 PSI operates the OPTIS facility for treatment of eye tumours. It was the first such installation in Western Europe, developed by PSI physicists. In close cooperation with the 'Hôpital Opthalmique' of the University of Lausanne by March 2008 nearly 5000 patients have been treated at PSI with this unique method, in which a proton beam is directed accurately onto the eye tumour.

Since 1996 PSI has also operated the only compact scanning gantry in the world for proton radiation therapy of deep-seated tumours. The spot-scanning technique developed at PSI enables malignant tumours to be targeted with high precision deep inside in the body, and their growth successfully stopped, without damaging healthy tissue around the target area. By March 2008, 320 patients, suffering from brain, head and neck, skull-base, spinal cord or abdominal tumours, had been treated at Gantry 1.

The excellent and promising results of patient treatment have led to the (Project PROSCAN) with the objectives to install a dedicated and compact superconducting proton accelerator and to develop a new Gantry (Gantry 2) with advanced 2-dimensional and fast parallel scanning features. The new compact superconducting cyclotron has been in operation since February 2007, and patient treatment at Gantry 2 began in November 2013. With these expansions, PSI is able to offer year-round treatment at its Center for Proton Therapy (CPT). As of 2015, work is ongoing on a third gantry with a similar specification to Gantry 2.[9]

The goals of these developments are to increase radiation precision of even moving tumours and to transfer the knowledge and proton therapy technology into hospital-based projects.

With the expansion of the facility, PSI will be able to strengthen the clinical research program and to treat more than 500 patients per year, including those with eye tumours.

Associated institutions

See also


  1. "Overview: Facts and figures of the Paul Scherrer Institute". Paul Scherrer Institute. Retrieved 13 June 2015.
  2. "Overview: SwissFEL – the new large-scale facility at the Paul Scherrer Institute". Paul Scherrer Institute. Archived from the original on 17 September 2014. Retrieved 17 September 2014.
  3. Kontakt: ABE-Web-Team. "The 590 MeV Ring Cyclotron of PSI". Retrieved 2013-06-25.
  5. "UCN Home Page". Retrieved 2013-06-25.
  6. "EDM Home Page". 2001-09-12. Retrieved 2013-06-25.
  7. Neutron electric dipole moment
  8. Paul Scherrer Institut (PSI) :: Large Scale Facilities , retrieved 2011-04-02
  9. "Proton Therapy at PSI". Retrieved 2015-10-20.
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