A synchrotron is a particular type of cyclic
particle accelerator, descended from the
cyclotron, in which the accelerating particle beam travels around a fixed closed-loop path. The
magnetic field
A magnetic field is a vector field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials. A moving charge in a magnetic field experiences a force perpendicular to its own velocity and to ...
which bends the particle beam into its closed path increases with time during the accelerating process, being ''synchronized'' to the increasing
kinetic energy
In physics, the kinetic energy of an object is the energy that it possesses due to its motion.
It is defined as the work needed to accelerate a body of a given mass from rest to its stated velocity. Having gained this energy during its acce ...
of the particles. 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
Large Hadron Collider
The Large Hadron Collider (LHC) is the world's largest and highest-energy particle collider. It was built by the European Organization for Nuclear Research (CERN) between 1998 and 2008 in collaboration with over 10,000 scientists and hundr ...
(LHC) near Geneva, Switzerland, built in 2008 by the
European Organization for Nuclear Research (CERN). It can accelerate beams of protons to an energy of 6.5 tera
electronvolts
In physics, an electronvolt (symbol eV, also written electron-volt and electron volt) is the measure of an amount of kinetic energy gained by a single electron accelerating from rest through an electric potential difference of one volt in v ...
(TeV or 10
12 eV).
The synchrotron principle was invented by
Vladimir Veksler
Vladimir Iosifovich Veksler (russian: Владимир Иосифович Векслер; ; March 4, 1907 – September 22, 1966) was a prominent Soviet experimental physicist.
Biography
Veksler was born in Zhitomir on March 4, 1907 in the ...
in 1944.
Edwin McMillan constructed the first electron synchrotron in 1945, arriving at the idea independently, having missed Veksler's publication (which was only available in a
Soviet
The Soviet Union,. officially the Union of Soviet Socialist Republics. (USSR),. was a List of former transcontinental countries#Since 1700, transcontinental country that spanned much of Eurasia from 1922 to 1991. A flagship communist state, ...
journal, although in English).
[
] The first proton synchrotron was designed by
Sir Marcus Oliphant and built in 1952.
Types
Several specialized types of synchrotron machines are used today:
*A
storage ring is a special type of synchrotron in which the kinetic energy of the particles is kept constant.
*A
synchrotron light source is a combination of different electron accelerator types, including a storage ring in which the desired electromagnetic radiation is generated. This radiation is then used in experimental stations located on different
beamlines. In addition to the storage ring, a synchrotron light source usually contains a
linear accelerator (linac) and another synchrotron which is sometimes called a ''booster'' in this context. The linac and the booster are used to successively accelerate the electrons to their final energy before they are magnetically "kicked" into the storage ring. Synchrotron light sources in their entirety are sometimes called "synchrotrons", although this is technically incorrect.
*A cyclic
collider is also a combination of different accelerator types, including two intersecting storage rings and the respective pre-accelerators.
Principle of operation
The synchrotron evolved from the
cyclotron, the first cyclic particle accelerator. While a classical
cyclotron uses both a constant guiding
magnetic field
A magnetic field is a vector field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials. A moving charge in a magnetic field experiences a force perpendicular to its own velocity and to ...
and a constant-frequency
electromagnetic field
An electromagnetic field (also EM field or EMF) is a classical (i.e. non-quantum) field produced by (stationary or moving) electric charges. It is the field described by classical electrodynamics (a classical field theory) and is the classical ...
(and is working in
classical approximation), its successor, the
isochronous cyclotron, works by local variations of the guiding magnetic field, adapting to the increasing
relativistic mass
The word " mass" has two meanings in special relativity: '' invariant mass'' (also called rest mass) is an invariant quantity which is the same for all observers in all reference frames, while the relativistic mass is dependent on the velocity ...
of particles during acceleration.
In a synchrotron, this adaptation is done by variation of the magnetic field strength in time, rather than in space. For particles that are not close to the speed of
light
Light or visible light is electromagnetic radiation that can be perceived by the human eye. Visible light is usually defined as having wavelengths in the range of 400–700 nanometres (nm), corresponding to frequencies of 750–420 t ...
, the frequency of the applied electromagnetic field may also change to follow their non-constant circulation time. By increasing these
parameter
A parameter (), generally, is any characteristic that can help in defining or classifying a particular system (meaning an event, project, object, situation, etc.). That is, a parameter is an element of a system that is useful, or critical, when ...
s 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 thin
torus
In geometry, a torus (plural tori, colloquially donut or doughnut) is a surface of revolution generated by revolving a circle in three-dimensional space about an axis that is coplanar with the circle.
If the axis of revolution does n ...
, 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.
While the first synchrotrons and storage rings like the
Cosmotron
The Cosmotron was a particle accelerator, specifically a proton synchrotron, at Brookhaven National Laboratory. Its construction was approved by the U.S. Atomic Energy Commission in 1948, reaching its full energy in 1953, and continuing to ru ...
and
ADA
Ada may refer to:
Places
Africa
* Ada Foah, a town in Ghana
* Ada (Ghana parliament constituency)
* Ada, Osun, a town in Nigeria
Asia
* Ada, Urmia, a village in West Azerbaijan Province, Iran
* Ada, Karaman, a village in Karaman Province, T ...
strictly used the toroid shape, the
strong focusing principle independently discovered by
Ernest Courant
Ernest Courant (March 26, 1920 – April 21, 2020) was an American accelerator physicist and a fundamental contributor to modern large-scale particle accelerator concepts. His most notable discovery was his 1952 work with Milton S. Livingston an ...
et al. and
Nicholas Christofilos 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 by
radio frequency cavities for direct acceleration,
dipole magnets (''bending magnets'') for deflection of particles (to close the path), and
quadrupole /
sextupole magnets for beam focusing.
The combination of time-dependent guiding magnetic fields and the strong focusing principle enabled the design and operation of modern large-scale accelerator facilities like
colliders and
synchrotron light sources. The straight sections along the closed path in such facilities are not only required for radio frequency cavities, but also for
particle detectors (in colliders) and photon generation devices such as
wigglers and
undulator
An undulator is an insertion device from high-energy physics and usually part of a larger
installation, a synchrotron storage ring, or it may be a component of a free electron laser. It consists of a periodic structure of dipole magnets. These ...
s (in third generation synchrotron light sources).
The maximum energy that a cyclic accelerator can impart is typically limited by the maximum strength of the magnetic fields and the minimum radius (maximum
curvature
In mathematics, curvature is any of several strongly related concepts in geometry. Intuitively, the curvature is the amount by which a curve deviates from being a straight line, or a surface deviates from being a plane.
For curves, the can ...
) of the particle path. Thus one method for increasing the energy limit is to use
superconducting magnet
A superconducting magnet is an electromagnet made from coils of superconducting wire. They must be cooled to cryogenic temperatures during operation. In its superconducting state the wire has no electrical resistance and therefore can conduct much ...
s, these not being limited by
magnetic saturation.
Electron
The electron ( or ) is a subatomic particle with a negative one elementary electric charge. Electrons belong to the first generation of the lepton particle family,
and are generally thought to be elementary particles because they have n ...
/
positron accelerators may also be limited by the emission of
synchrotron radiation
Synchrotron radiation (also known as magnetobremsstrahlung radiation) is the electromagnetic radiation emitted when relativistic charged particles are subject to an acceleration perpendicular to their velocity (). It is produced artificially in ...
, 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.
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 of
electron
The electron ( or ) is a subatomic particle with a negative one elementary electric charge. Electrons belong to the first generation of the lepton particle family,
and are generally thought to be elementary particles because they have n ...
/
positron accelerators is limited by this radiation loss, while this does not play a significant role in the dynamics of
proton
A proton is a stable subatomic particle, symbol , H+, or 1H+ with a positive electric charge of +1 ''e'' elementary charge. Its mass is slightly less than that of a neutron and 1,836 times the mass of an electron (the proton–electron mass ...
or
ion accelerators. The energy of such accelerators is limited strictly by the strength of magnets and by the cost.
Injection procedure
Unlike in 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-accelerated
particle beams into a synchrotron. The pre-acceleration can be realized by a chain of other accelerator structures like a
linac, a
microtron or another synchrotron; all of these in turn need to be fed by a particle source comprising a simple high voltage power supply, typically a
Cockcroft-Walton generator.
Starting from an appropriate initial value determined by the injection energy, the field strength of the
dipole 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 new ''injection cycle''. Depending on the method of magnet control used, the time interval for one cycle can vary substantially between different installations.
In large-scale facilities
One of the early large synchrotrons, now retired, is the
Bevatron, constructed in 1950 at the
Lawrence Berkeley Laboratory. The name of this
proton
A proton is a stable subatomic particle, symbol , H+, or 1H+ with a positive electric charge of +1 ''e'' elementary charge. Its mass is slightly less than that of a neutron and 1,836 times the mass of an electron (the proton–electron mass ...
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
transuranium elements
The transuranium elements (also known as transuranic elements) are the chemical elements with atomic numbers greater than 92, which is the atomic number of uranium. All of these elements are unstable and decay radioactively into other 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.
Another early large synchrotron is the
Cosmotron
The Cosmotron was a particle accelerator, specifically a proton synchrotron, at Brookhaven National Laboratory. Its construction was approved by the U.S. Atomic Energy Commission in 1948, reaching its full energy in 1953, and continuing to ru ...
built at
Brookhaven National Laboratory which reached 3.3 GeV in 1953.
The Cosmotron
/ref>
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.
As part of colliders
Until August 2008, the highest energy collider in the world was the Tevatron, at the Fermi National Accelerator Laboratory, in the United States
The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country Continental United States, primarily located in North America. It consists of 50 U.S. state, states, a Washington, D.C., ...
. It accelerated protons
A proton is a stable subatomic particle, symbol , H+, or 1H+ with a positive electric charge of +1 ''e'' elementary charge. Its mass is slightly less than that of a neutron and 1,836 times the mass of an electron (the proton–electron m ...
and antiprotons
The antiproton, , (pronounced ''p-bar'') is the antiparticle of the proton. Antiprotons are stable, but they are typically short-lived, since any collision with a proton will cause both particles to be annihilated in a burst of energy.
The exis ...
to slightly less than 1 TeV
TEV may refer to:
* Transient Earth Voltage: a term for voltages appearing on the metal work of switchgear due to internal partial discharges
* TeV, or teraelectronvolt or trillion electron volt, a measure of energy
* Total Enterprise Value, a ...
of kinetic energy and collided them together. The Large Hadron Collider
The Large Hadron Collider (LHC) is the world's largest and highest-energy particle collider. It was built by the European Organization for Nuclear Research (CERN) between 1998 and 2008 in collaboration with over 10,000 scientists and hundr ...
(LHC), which has been built at the European Laboratory for High Energy Physics (CERN
The European Organization for Nuclear Research, known as CERN (; ; ), is an intergovernmental organization that operates the largest particle physics laboratory in the world. Established in 1954, it is based in a northwestern suburb of Gen ...
), has roughly seven times this energy (so proton-proton collisions occur at roughly 14 TeV). It is housed 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 LHC will also accelerate heavy ions (such as lead
Lead is a chemical element with the symbol Pb (from the Latin ) and atomic number 82. It is a heavy metal that is denser than most common materials. Lead is soft and malleable, and also has a relatively low melting point. When freshly cut, ...
) up to an energy of 1.15 PeV.
The largest device of this type seriously proposed was the Superconducting Super Collider (SSC), which was to be built in the United States
The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country Continental United States, primarily located in North America. It consists of 50 U.S. state, states, a Washington, D.C., ...
. This design, like others, used superconducting magnet
A superconducting magnet is an electromagnet made from coils of superconducting wire. They must be cooled to cryogenic temperatures during operation. In its superconducting state the wire has no electrical resistance and therefore can conduct much ...
s 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 naïve cost estimation and economic management issues rather than any basic engineering flaws. It can also be argued that the end of the Cold War
The Cold War is a term commonly used to refer to a period of geopolitical tension between the United States and the Soviet Union and their respective allies, the Western Bloc and the Eastern Bloc. The term '' cold war'' is used because t ...
resulted in a change of scientific funding priorities that contributed to its ultimate cancellation. 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 to synchrotron radiation
Synchrotron radiation (also known as magnetobremsstrahlung radiation) is the electromagnetic radiation emitted when relativistic charged particles are subject to an acceleration perpendicular to their velocity (). It is produced artificially in ...
. This will require a return to the linear accelerator, but with devices significantly longer than those currently in use. There is at present a major effort to design and build the International Linear Collider
The International Linear Collider (ILC) is a proposed linear particle accelerator. It is planned to have a collision energy of 500 GeV initially, with the possibility for a later upgrade to 1000 GeV (1 TeV). Although early propose ...
(ILC), which will consist of two opposing linear accelerators
A linear particle accelerator (often shortened to linac) is a type of particle accelerator that accelerates charged subatomic particles or ions to a high speed by subjecting them to a series of oscillating electric potentials along a linear b ...
, one for electrons and one for positrons. These will collide at a total center of mass
In physics, the center of mass of a distribution of mass in space (sometimes referred to as the balance point) is the unique point where the weighted relative position of the distributed mass sums to zero. This is the point to which a force may ...
energy of 0.5 TeV
TEV may refer to:
* Transient Earth Voltage: a term for voltages appearing on the metal work of switchgear due to internal partial discharges
* TeV, or teraelectronvolt or trillion electron volt, a measure of energy
* Total Enterprise Value, a ...
.
As part of synchrotron light sources
Synchrotron radiation also has a wide range of applications (see synchrotron light
Synchrotron radiation (also known as magnetobremsstrahlung radiation) is the electromagnetic radiation emitted when relativistic charged particles are subject to an acceleration perpendicular to their velocity (). It is produced artificially in ...
) and many 2nd and 3rd generation synchrotrons have been built especially to harness it. The largest of those 3rd generation synchrotron light sources are the European Synchrotron Radiation Facility (ESRF) in Grenoble, France, the Advanced Photon Source ( APS) near Chicago, USA, and SPring-8 in Japan
Japan ( ja, 日本, or , and formally , ''Nihonkoku'') is an island country in East Asia. It is situated in the northwest Pacific Ocean, and is bordered on the west by the Sea of Japan, while extending from the Sea of Okhotsk in the n ...
, accelerating electrons up to 6, 7 and 8 GeV, respectively.
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. More compact models, however, have been developed, such as the Compact Light Source.
Applications
* Life sciences: protein
Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, res ...
and large-molecule crystallography
* LIGA based microfabrication
* Drug discovery and research
* X-ray lithography
X-ray lithography is a process used in semiconductor device fabrication industry to selectively remove parts of a thin film of photoresist. It uses X-rays to transfer a geometric pattern from a mask to a light-sensitive chemical photoresist, o ...
* X-ray microtomography
* Analysing chemicals to determine their composition
* Observing the reaction of living cells to drugs
* Inorganic material crystallography and microanalysis
* Fluorescence
Fluorescence is the emission of light by a substance that has absorbed light or other electromagnetic radiation. It is a form of luminescence. In most cases, the emitted light has a longer wavelength, and therefore a lower photon energy, tha ...
studies
* Semiconductor
A semiconductor is a material which has an electrical conductivity value falling between that of a conductor, such as copper, and an insulator, such as glass. Its resistivity falls as its temperature rises; metals behave in the opposite way ...
material analysis and structural studies
* Geological material analysis
* Medical imaging
Medical imaging is the technique and process of imaging the interior of a body for clinical analysis and medical intervention, as well as visual representation of the function of some organs or tissues (physiology). Medical imaging seeks to re ...
* Particle therapy to treat some forms of cancer
Cancer is a group of diseases involving abnormal cell growth with the potential to invade or spread to other parts of the body. These contrast with benign tumors, which do not spread. Possible signs and symptoms include a lump, abnormal b ...
* Radiometry
Radiometry is a set of techniques for measuring electromagnetic radiation, including visible light. Radiometric techniques in optics characterize the distribution of the radiation's power in space, as opposed to photometric techniques, which ch ...
: calibration of detectors and radiometric standards
See also
* List of synchrotron radiation facilities
This is a table of synchrotrons and storage rings used as synchrotron radiation sources, and free electron laser
A free-electron laser (FEL) is a (fourth generation) light source producing extremely brilliant and short pulses of radiation. An FE ...
* Synchrotron radiation
Synchrotron radiation (also known as magnetobremsstrahlung radiation) is the electromagnetic radiation emitted when relativistic charged particles are subject to an acceleration perpendicular to their velocity (). It is produced artificially in ...
* Cyclotron radiation
* Computed X-ray tomography
* Energy amplifier In nuclear physics, an energy amplifier is a novel type of nuclear power reactor, a subcritical reactor, in which an energetic particle beam is used to stimulate a reaction, which in turn releases enough energy to power the particle accelerator and ...
* Superconducting radio frequency
* Coherent diffraction imaging
Coherent diffractive imaging (CDI) is a "lensless" technique for 2D or 3D reconstruction of the image of nanoscale structures such as nanotubes, nanocrystals, porous nanocrystalline layers, defects, potentially proteins, and more. In CDI, a highl ...
References
External links
ESRF (European Synchrotron Radiation Facility)
National Synchrotron Radiation Research Center (NSRRC) in Taiwan
Elettra Sincrotrone Trieste - Elettra and Fermi lightsources
Canadian Light Source
Australian Synchrotron
French synchrotron Soleil
Diamond UK Synchrotron
Lightsources.org
IAEA database of electron synchrotron and storage rings
CERN Large Hadron Collider
A Miniature Synchrotron:
room-size synchrotron offers scientists a new way to perform high-quality x-ray experiments in their own labs, ''Technology Review'', February 4, 2008
Brazilian Synchrotron Light Laboratory
Podcast interview
with a scientist at the European Synchrotron Radiation Facility
Spanish ALBA Light Source
The tabletop synchrotron MIRRORCLE
SOLARIS synchrotron in Poland
{{Authority control
Accelerator physics
Synchrotron-related techniques
Particle accelerators