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Synchrotron

A synchrotron is a particular type of cyclic particle accelerator. While a cyclotron uses a constant magnetic field (to cause the particles to circulate) and a constant frequency of applied electric field (to cause the particles to accelerate), and one of these is varied in the synchrocyclotron, each of these is varied in the synchrotron. By varying both of these parameters appropriately the path of the particles is constant during acceleration. This allows the vacuum container for the particles to be a torus (commonly described as a "doughnut shape"). This is easily constructed in large diameters using simple pipe segments, unlike the disk shaped chamber of the cyclotron type devices. The shape also allows the use of multiple magnets to bend the particle beam.

The particles are accelerated an evacuated pipe that is bent to form a large circle. The maximum energy that a cyclic accelerator can impart is determined by the strength of the magnetic field and the maximum radius of the circle that the particles travel in.

In a cyclotron the maximum radius is quite limited as the particles start at the center and spiral outward, thus this entire path must be a self supporting disk-shaped evacuated chamber. Since the radius is limited the power of the machine becomes limited by the strength of the magnetic field. The arrangement of the single magnet also limits the economic size of the device.

Synchrotrons overcome these limitations. The power of this device in accelerating electrons is limited by synchrotron radiation, which causes particles moving in a circular path to loose energy. At some point it becomes impractical to make up this energy. More powerful devices for accelerating protons and heavier particles are built by using large radius paths and by using more numerous and more powerful magnets to bend the particle beam.

One of the early large synchrotrons, still operating, is the Bevatron, constructed in 1950 at the Lawrence Berkeley Laboratory. The name of this proton accelerator comes from its power, in the range of 6.3 BEVs (billion electron volts). A number of heavy elements, unseen in the natural world, were first created with this machine. This site is also the location of one of the first large bubble chambers used to examine the results of the atomic collisions produced here.

The largest device of this type yet proposed was the Superconducting Super Collider (SSC). This design uses superconducting magnets. While construction was begun this machine was not completed owing to the great expense. It appears that expense is the limiting factor in proton and heavy particle accelerators.

While there is still usefulness for yet more powerful proton and heavy particle cyclic accelerators it appears that the next step up in electron acceleration power must avoid losses to synchrotron radiation. This will require a return to the linear accelerator, but with devices significantly longer than those currently in use.

Synchrotron radiation is useful for some applications and some synchrotrons have been built especially to produce this as "synchrotron light" - see the article linked for some applications. Currently the Advanced Photon Source is the synchrotron for this type of application with the largest user community.

List of synchrotrons

Synchrotrons of the World

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