Synchrotron

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This article is concerned with the synchrotron device - a sub-atomic particle accelerator. For applications of the synchrotron radiation produced by cyclic particle accelerators see synchrotron light.

A synchrotron is a particular type of cyclic particle accelerator in which the magnetic field (to turn the particles so they circulate) and the electric field (to accelerate the particles) are carefully synchronized with the travelling particle beam.

Characteristics

File:Schéma de principe du synchrotron.jpg
Synchrotrons are now mostly used for producing high intensity X-ray beams; here, the synchrotron is the circular track, off which the beamlines branch.

While a cyclotron uses a constant magnetic field and a constant-frequency applied electric field, and one of these is varied in the synchrocyclotron, both of these are varied in the synchrotron. By increasing these parameters appropriately as the particles gain energy, their path can be held constant as they are accelerated. This allows the vacuum container for the particles to be a large thin torus (commonly described as a "doughnut shape"). In reality it is easier to use some straight sections and some bent sections giving the "doughnut shape" the shape of a rounded cornered polygon. A path of large effective radius may thus be constructed using simple straight and curved pipe segments, unlike the disc-shaped chamber of the cyclotron type devices. The shape also allows and requires the use of multiple magnets to bend the particle beam.

The maximum energy that a cyclic accelerator can impart is typically limited by the strength of the magnetic field(s) and the maximum radius of the particle path.

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 disc-shaped evacuated chamber. Since the radius is limited, the power of the machine becomes limited by the strength of the magnetic field. In the case of an ordinary (not superconducting) electromagnet the field strength is limited by the saturation of the core (when all magnetic domains are aligned the field may not be further increased to any practical extent). The arrangement of the single pair of magnets the full width of the device also limits the economic size of the device.

Synchrotrons overcome these limitations, allowing a narrow beam pipe which can be surrounded by much smaller and more tightly focused magnets. The ability of this device to accelerate particles is limited by the fact that the particles must be charged to be accelerated at all, but charged particles under acceleration emit photons (light), thereby losing 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. More powerful accelerators are built by using large radius paths and by using more numerous and more powerful microwave cavities to accelerate the particle beam between corners. Lighter particles (such as electrons) lose a larger fraction of their energy when turning. Practically speaking, the energy of electron/positron accelerators is limited by this radiation loss, while it does not play a significant role in the dynamics of proton or ion accelerators. The energy of those is limited strictly by the strength of magnets and by the cost.

Large synchrotrons

File:SOLEIL le 01 juin 2005.jpg
Modern industrial-scale synchrotrons are very large equipments (here, Soleil near Paris)

One of the early large synchrotrons, now retired, 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 GeV (then called BeV for billion electron volts; the name predates the adoption of the SI prefix giga). 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.

Currently, the highest energy synchrotron in the world is the Tevatron, at the Fermi National Accelerator Laboratory, in the United States. It accelerates protons and antiprotons to nearly 1 TeV of kinetic energy and collides them together. The Large Hadron Collider (LHC), which is being built at the European Laboratory for High Energy Physics (CERN), will have roughly seven times this energy, and is scheduled to turn on in 2007. It is being built in the 27 km tunnel which formerly housed the Large Electron Positron (LEP) collider, so it will maintain the claim as the largest scientific device ever built.

The largest device of this type yet seriously proposed was the Superconducting Super Collider (SSC), to be built in the United States. This design uses superconducting magnets which allow more intense magnetic fields to be created without the limitations of core saturation. While construction was begun, the project was cancelled in 1994, citing excessive budget overruns — this was due to naive cost estimation and economic management issues rather than any basic engineering flaws. It can also be argued that the end of the Cold War resulted in a change of scientific funding priorities that contributed to its ultimate cancellation.

While there is still potential for yet more powerful proton and heavy particle cyclic accelerators, it appears that the next step up in electron acceleration power must avoid losses due to synchrotron radiation. This will require a return to the linear accelerator, but with devices significantly longer than those currently in use. There is a present a major effort to design and build the International Linear Collider (ILC), which will consist of two opposing linear accelerators, one for electrons and one for positrons. These will collide at a total center of mass energy of 500 GeV.

However many scientists use synchrotron radiation (see synchrotron light) and for them the production of synchrotron radiation is the only purpose of a synchrotron.

Synchrotron radiation is useful for a wide range of applications and many synchrotrons have been built especially to produce synchrotron light. SPring-8 in Japan is one of them, providing the world's most powerful (as of 2005) electron acceleration capacity of 8 GeV.

Synchrotrons which are useful for cutting edge research are large machines, 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. These installations are mostly built by the science funding agencies of governments of developed countries, or by collaborations between several countries in a region, and operated as infrastructure facilities available to scientists from universities and research organisations throughout the country, region, or world.

List of synchrotron radiation facilities

  • Advanced Light Source (ALS), Berkeley, California
  • Advanced Photon Source (APS), Argonne, Illinois
  • ANKA Synchrotron Strahlungsquelle, Karlsruhe, Germany (See also the English version)
  • Australian Synchrotron, Melbourne, Victoria (Under construction)
  • Beijing Synchrotron Radiation Facility (BSRF), Beijing
  • Berliner Elektronenspeicherring-Gesellschaft für Synchrotronstrahlung (BESSY), Berlin
  • Canadian Light Source (CLS), Saskatoon, Saskatchewan
  • Center for Advanced Microstructures and Devices (CAMD), Baton Rouge, Louisiana
  • Center for Advanced Technology (INDUS-1 and INDUS-2), Indore, India
  • Cornell High Energy Synchrotron Source (CHESS), Ithaca, New York
  • diamond, Rutherford Appleton Laboratory, Didcot, England
  • Dortmund Electron Test Accelerator (DELTA), Dortmund, Germany
  • Electron Stretcher Accelerator (ELSA), Bonn, Germany (See also the German version)
  • Electrotechnical Laboratory (ETL) Electron Accelerator Facility (NIJI-II, NIJI-IV, TERAS), *Tsukuba, Japan (See also the English version)
  • Elettra Synchrotron Light Source, Trieste, Italy
  • European Synchrotron Radiation Facility (ESRF), Grenoble, France
  • Hamburger Synchrotronstrahlungslabor (HASYLAB) at DESY, Hamburg, Germany
  • Institute for Storage Ring Facilities (ISA, ASTRID), Aarhus, Denmark
  • Laboratoire pour l'Utilisation du Rayonnement Electromagnétique (LURE), Orsay, France (See also the English version)
  • Consorci per a la construcció i explotació del Lab. de Llum Sincrotró (ALBA), Barcelona, Spain (under construction)
  • Laboratório Nacional de Luz Síncrotron (LNLS), Campinas, Brazil
  • MAX-lab, Lund, Sweden
  • Nano-hana Project, Ichihara, Japan (See also the Japanese version)
  • National Synchrotron Light Source (NSLS), Brookhaven, New York
  • National Synchrotron Radiation Laboratory (NSRL), Hefei, China
  • National Synchrotron Radiation Research Center (NSRRC), Hsinchu, Taiwan, R.O.C
  • National Synchrotron Research Center (NSRC), Nakhon Ratchasima, Thailand
  • Photon Factory (PF) at KEK, Tsukuba, Japan (See also the Japanese version)
  • Pohang Accelerator Laboratory, Pohang, Korea (See also the Korean version)
  • Siberian Synchrotron Radiation Centre (SSRC), Novosibirsk, Russia
  • Singapore Synchrotron Light Source (SSLS), Singapore
  • Soleil , near Paris, France
  • Stanford Synchrotron Radiation Laboratory (SSRL), Menlo Park, California - division of Stanford Linear Accelerator Center
  • Super Photon Ring - 8 GeV (SPring-8), Nishi-Harima, Japan (See also the Japanese version)
  • Swiss Light Source (SLS), Villigen, Switzerland
  • Synchrotron Light Laboratory (LLS), Barcelona, Spain
  • Synchrotron Radiation Center (SRC), Madison, Wisconsin
  • Synchrotron Radiation Source (SRS), Daresbury, U.K.
  • Synchrotron Ultraviolet Radiation Facilty (SURF III) at the National Institute of Standards and Technology (NIST), Gaithersburg, Maryland
  • UVSOR Facility, Okazaki, Japan (See also the English version)
  • VSX Light Source, Kashiwa, Japan (See also the Japanese version)

Applications

  • Life sciences: protein and large molecule crystallography
  • Drug discovery and research
  • "Burning" computer chip designs into metal wafers
  • Studying molecule shapes and protein crystals
  • Analysing chemicals to determine their composition
  • Watching living cells as they react to drugs
  • Inorganic material crystallography and microanalysis
  • Fluorescence studies
  • Semiconductor material analysis and structural studies
  • Geological material analysis
  • Medical imaging

External links

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