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Synchrotron

physical science Maturity 9-11 Next article →

A synchrotron is a specific type of cyclic particle accelerator. It is a machine designed to move tiny particles, such as protons or electrons, around a fixed closed-loop path. This technology is a descendant of the cyclotron, which was the first cyclic accelerator. Synchrotrons are vital to modern science because they allow for the construction of massive, large-scale facilities. By separating the tasks of bending, focusing, and accelerating particles into different components, engineers can build much larger machines than before.

Aust.-Synchrotron-Interior-Panorama,-14.06.2007
Aust.-Synchrotron-Interior-Panorama,-14.06.2007

The mechanism of a synchrotron relies on careful synchronization. Unlike a cyclotron, a synchrotron cannot accelerate particles starting from zero kinetic energy. Instead, particles are first pre-accelerated by a device like a linear accelerator, or linac. These particles are then injected into the main ring. As the particles gain kinetic energy, the strength of the magnetic field must increase at the same time. This ensures the particles stay on their constant circular or polygonal path.

Cosmotron (PSF)
Cosmotron (PSF)

The machine also varies the radio frequency (RF) of the electromagnetic field to match the particles' changing circulation time. This precise timing allows the vacuum chamber to be a large, thin torus rather than a thick disk.

Several specialized types of synchrotrons exist to serve different scientific goals. A collider is a machine where two particle beams travel in countercirculating rings. These beams collide head-on to create much higher-energy collisions than a stationary target could. A storage ring is a specialized version where the kinetic energy of the particles is kept constant. Finally, there are synchrotron light sources. These use a combination of accelerators and storage rings to generate intense electromagnetic radiation.

University of Michigan synchrotron
University of Michigan synchrotron

This radiation is then sent to experimental stations along various beamlines.

Modern synchrotrons use specific components to manage the particle beam. Dipole magnets, also called bending magnets, are used to deflect particles to close the loop. Radio frequency cavities provide the direct acceleration needed to increase energy. To keep the beam from spreading out, scientists use quadrupole and sextupole magnets for beam focusing. The discovery of the strong focusing principle by Ernest Courant and Nicholas Christofilos allowed designers to shape the path into a round-cornered polygon. This made it possible to include straight sections for detectors or photon-generating devices like wigglers and undulators.

The history of the synchrotron began in the mid-1940s. Vladimir Veksler proposed the synchrotron principle in 1944. In 1945, Edwin McMillan built the first electron synchrotron after arriving at the idea independently. Later, Sir Marcus Oliphant designed the first proton synchrotron, which was built at the University of Birmingham in 1952.

Birmingham proton synchrotron 07 (cropped)
Birmingham proton synchrotron 07 (cropped)

In 1963, McMillan and Veksler were jointly awarded the Atoms for Peace Prize. Early large machines like the Bevatron at the Lawrence Berkeley Laboratory helped discover the antiproton in 1955. This discovery earned Owen Chamberlain and Emilio Segrè the Nobel Prize in Physics in 1959.

Today, the scale of these machines is truly massive. The largest particle accelerator in the world is the Large Hadron Collider (LHC) near Geneva, Switzerland. Completed in 2008 by CERN, the LHC sits in a 27.6 km tunnel. It can accelerate proton beams to an energy of 7 teraelectronvolts (TeV). It can also accelerate heavy ions, such as lead, up to 1.15 PeV upon collision. Other large light sources include the European Synchrotron Radiation Facility in France and the Advanced Photon Source in the United States. These facilities cost hundreds of millions of dollars to build.

There are physical limits to how much energy a synchrotron can impart. The maximum energy is usually limited by the strength of the magnetic fields and the radius of the path. To overcome this, some machines use superconducting magnets to avoid magnetic saturation. Electron and positron accelerators also face a unique limit called synchrotron radiation. As these lighter particles are deflected, they lose kinetic energy through radiation. This loss eventually equals the energy added by the machine, reaching a limit. For protons and ions, this radiation loss is not a significant factor in their dynamics.

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🖼️ Images & Media (5)
File:University of Michigan synchrotron.jpg
University of Michigan synchrotron.jpg
File:Cosmotron (PSF).png
Cosmotron (PSF).png
File:Aust.-Synchrotron-Interior-Panorama,-14.06.2007.jpg
Aust.-Synchrotron-Interior-Panorama,-14.06...
File:Birmingham proton synchrotron 07 (cropped).jpg
Birmingham proton synchrotron 07 (cropped).jpg
File:Taipei_Veterans_General_Hospital_Heavy_Ion_Therapy_Center_2023-05-15_03.jpg
Taipei_Veterans_General_Hospital_Heavy_Ion...
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