Asynchrotron is a particular type of cyclicparticle accelerator, descended from thecyclotron, in which the accelerating particle beam travels around a fixed closed-loop path. The strength of themagnetic field which bends the particle beam into its closed path increases with time during the accelerating process, beingsynchronized to the increasingkinetic energy of the particles.[1]
The synchrotron is one of the first accelerator concepts to enable the construction of large-scale facilities, since bending, beam focusing and acceleration can be separated into different components. The most powerful modern particle accelerators use versions of the synchrotron design. The largest synchrotron-type accelerator, also the largest particle accelerator in the world, is the 27-kilometre-circumference (17 mi)Large Hadron Collider (LHC) near Geneva, Switzerland, completed in 2008 by theEuropean Organization for Nuclear Research (CERN).[2] It can accelerate beams of protons to an energy of 7teraelectronvolts (TeV or 1012 eV).
Large synchrotrons usually have alinear accelerator (linac) to give the particles an initial acceleration, and a lower energy synchrotron which is sometimes called abooster to increase the energy of the particles before they are injected into the high energy synchrotron ring. Several specialized types of synchrotron machines are used today:
The synchrotron evolved from thecyclotron, the first cyclic particle accelerator. While a classicalcyclotron uses both a constant guidingmagnetic field and a constant-frequencyelectromagnetic field (and is working inclassical approximation), its successor, theisochronous cyclotron, works by local variations of the guiding magnetic field, adapting to the increasingrelativistic mass of particles during acceleration.[6]
.png)
In a synchrotron, the strength of magnetic field and RF frequency is varied during acceleration.[6] For particles that are not close to the speed oflight, the frequency of the applied electromagnetic field may also change to follow their non-constant circulation time. By increasing theseparameters accordingly as the particles gain energy, their circulation path can be held constant as they are accelerated. This allows the vacuum chamber for the particles to be a large thintorus, rather than a disk as in previous, compact accelerator designs. Also, the thin profile of the vacuum chamber allowed for a more efficient use of magnetic fields than in a cyclotron, enabling the cost-effective construction of larger synchrotrons.[citation needed]
While the first synchrotrons and storage rings like theCosmotron andADA strictly used the toroid shape, thestrong focusing principle independently discovered byErnest Courant et al.[7][8] andNicholas Christofilos[9] allowed the complete separation of the accelerator into components with specialized functions along the particle path, shaping the path into a round-cornered polygon. Some important components are given byradio frequency cavities for direct acceleration,dipole magnets (bending magnets) for deflection of particles (to close the path), andquadrupole /sextupole magnets for beam focusing.[10]
The combination of time-dependent guiding magnetic fields and the strong focusing principle enabled the design and operation of modern large-scale accelerator facilities likecolliders andsynchrotron light sources. The straight sections along the closed path in such facilities are not only required for radio frequency cavities, but also forparticle detectors (in colliders) and photon generation devices such aswigglers andundulators (in third generation synchrotron light sources).[citation needed]
The maximum energy that a cyclic accelerator can impart is typically limited by the maximum strength of the magnetic fields and the minimum radius (maximumcurvature) of the particle path. Thus one method for increasing the energy limit is to usesuperconducting magnets, these not being limited bymagnetic saturation.Electron/positron accelerators may also be limited by the emission ofsynchrotron radiation, resulting in a partial loss of the particle beam's kinetic energy. The limiting beam energy is reached when the energy lost to the lateral acceleration required to maintain the beam path in a circle equals the energy added each cycle.[citation needed]
More powerful accelerators are built by using large radius paths and by using more numerous and more powerful microwave cavities. Lighter particles (such as electrons) lose a larger fraction of their energy when deflected. Practically speaking, the energy ofelectron/positron accelerators is limited by this radiation loss, while this does not play a significant role in the dynamics ofproton orion accelerators. The energy of such accelerators is limited strictly by the strength of magnets and by the cost.[citation needed]
Unlike a cyclotron, synchrotrons are unable to accelerate particles from zero kinetic energy; one of the obvious reasons for this is that its closed particle path would be cut by a device that emits particles. Thus, schemes were developed to inject pre-acceleratedparticle beams into a synchrotron. The pre-acceleration can be realized by a chain of other accelerator structures like alinac, amicrotron or another synchrotron; all of these in turn need to be fed by a particle source comprising a simple high voltage power supply, typically aCockcroft–Walton generator.[citation needed]
Starting from an appropriate initial value determined by the injection energy, the field strength of thedipole magnets is then increased. If the high energy particles are emitted at the end of the acceleration procedure, e.g. to a target or to another accelerator, the field strength is again decreased to injection level, starting a newinjection cycle. Depending on the method of magnet control used, the time interval for one cycle can vary substantially between different installations.[citation needed]
The synchrotron principle was proposed byVladimir Veksler in 1944.[11]Edwin McMillan constructed the first electron synchrotron in 1945, arriving at the idea independently, having missed Veksler's publication (which was only available in aSoviet journal, although in English).[12][13][14]
.jpg)
The first proton synchrotron was designed bySir Marcus Oliphant[13][15] and constructed at theUniversity of Birmingham in 1952.[13] In 1963, McMillan and Veksler were jointly awarded the Atoms for Peace Prize for the invention of the synchrotron.[13]
One of the early large synchrotrons is theBevatron, constructed in 1950 at theLawrence Berkeley Laboratory. The Bevatron can accelerate a proton with an energy of 6.2GeV[16](then called BeV for billionelectron volts; the name predates the adoption of theSI prefixgiga-).[17] It can also accelerate heavier ions, such asdeuterons,alpha-particles, andnitrogen.[18] A number oftransuranium elements, unseen in the natural world, were first created with this instrument. This site is also the location of one of the first largebubble chambers are produced to examine the results of atomic collisions produced here.[19] In 1955, physicistsOwen Chamberlain andEmilio Segrè had used the Bevatron to detect evidence for the existence of antiproton, for which they received the 1959 Nobel Prize in Physics.[20] The Bevatron was retired in February 1993.[21]
Another early large synchrotron is theCosmotron built atBrookhaven National Laboratory which reached 3.3 GeV in 1953.[22]
In the 1980s, detail about the second generation of synchrotrons began to emerge. These devices were constructed specifically for experiments with producing synchrotron radiation rather than particle physics research[23] The 2 GeV Synchrotron Radiation Source (SRS) at Daresbury, England, which operated in 1981, was the first of these "second-generation" synchrotron sources. Additionally, first generation synchrotrons are upgraded to become second generation sources.[24]
Until August 2008, the highest energy collider in the world was theTevatron, at theFermi National Accelerator Laboratory, in theUnited States. It acceleratedprotons andantiprotons to slightly less than 1TeV of kinetic energy and collided them together. TheLarge Hadron Collider (LHC), which has been built at the European Laboratory for High Energy Physics (CERN), has roughly seven times this energy (so proton-proton collisions occur at roughly 14 TeV). It is housed in the 27.6 km tunnel which formerly housed the Large Electron Positron (LEP) collider.[25] The LHC will also accelerate heavy ions (such aslead) up to an energy of 1.15PeV upon collision.[26] As of 2025, it is considered the largest and most powerful particle colldier.[27]
The largest device of this type seriously proposed was theSuperconducting Super Collider (SSC), which was to be built in theUnited States. This design, like others, usedsuperconducting magnets which allow more intense magnetic fields to be created without the limitations of core saturation.[28]: 10 While construction was begun, the project was cancelled in 1994, citing excessivebudget overruns due to naïve cost estimation and economic management issues.[28]: 232–233 It can also be argued that the end of theCold War resulted in a change of scientific funding priorities that contributed to its ultimate cancellation.[28]: 232–233 However, the tunnel built for its placement still remains, although empty. While there is still potential for yet more powerful proton and heavy particle cyclic accelerators, it appears that the next step up in electron beam energy must avoid losses due tosynchrotron radiation. This will require a return to thelinear accelerator, but with devices significantly longer than those currently in use. There is at present a major effort to design and build theInternational Linear Collider (ILC), which will consist of two opposinglinear accelerators, one for electrons and one for positrons. These will collide at a totalcenter of mass energy of 0.5TeV.[citation needed]
Synchrotron radiation has a wide range of applications (seesynchrotron light) and many second and third generation synchrotrons have been built especially to harness it. The largest of those 3rd generation synchrotron light sources are theEuropean Synchrotron Radiation Facility (ESRF) inGrenoble, France, theAdvanced Photon Source (APS) inLemont, United States, andSPring-8 inHyōgo,Japan, accelerating electrons up to 6, 7 and 8GeV, respectively.[29][30][31]
Synchrotrons are large devices, costing tens or hundreds of millions of dollars to construct, and each beamline (there may be 20 to 50 at a large synchrotron) costs another two or three million dollars on average.[32][33] These installations also require a large footprint. More compact models, such as the Munich Compact Light Source, have been developed and tested.[34]
Among the few synchrotrons around the world, 16 are located in the United States. Many of them belong to national laboratories; few are located in universities.[35]
| International | |
|---|---|
| National | |
| Other | |
