Synchrotron radiation (also known as magnetobremsstrahlung radiation) is the electromagnetic radiation emitted when charged particles are accelerated radially, i.e., when they are subject to an acceleration perpendicular to their velocity (a ⊥ v). It is produced, for example, in synchrotrons using bending magnets, undulators and/or wigglers. If the particle is non-relativistic, then the emission is called cyclotron emission. If, on the other hand, the particles are relativistic, sometimes referred to as ultrarelativistic, the emission is called synchrotron emission. Synchrotron radiation may be achieved artificially in synchrotrons or storage rings, or naturally by fast electrons moving through magnetic fields. The radiation produced in this way has a characteristic polarization and the frequencies generated can range over the entire electromagnetic spectrum which is also called continuum radiation.
Syncradiation was named after its discovery in Schenectady, New York from a General Electric synchrotron accelerator built in 1946 and announced in May 1947 by Frank Elder, Anatole Gurewitsch, Robert Langmuir and Herb Pollock in a letter entitled "Radiation from Electrons in a Synchrotron". Pollock recounts:
On April 24, Langmuir and I were running the machine and as usual were trying to push the electron gun and its associated pulse transformer to the limit. Some intermittent sparking had occurred and we asked the technician to observe with a mirror around the protective concrete wall. He immediately signaled to turn off the synchrotron as "he saw an arc in the tube." The vacuum was still excellent, so Langmuir and I came to the end of the wall and observed. At first we thought it might be due to Cherenkov radiation, but it soon became clearer that we were seeing Ivanenko and Pomeranchuk radiation.
When high-energy particles are in acceleration, including electrons forced to travel in a curved path by a magnetic field, synchrotron radiation is produced. This is similar to a radio antenna, but with the difference that, in theory, the relativistic speed will change the observed frequency due to the Doppler effect by the Lorentz factor, γ. Relativistic length contraction then bumps the frequency observed by another factor of γ, thus multiplying the GHz frequency of the resonant cavity that accelerates the electrons into the X-ray range. The radiated power is given by the relativistic Larmor formula while the force on the emitting electron is given by the Abraham–Lorentz–Dirac force.
The radiation pattern can be distorted from an isotropic dipole pattern into an extremely forward-pointing cone of radiation. Synchrotron radiation is the brightest artificial source of X-rays.
The planar acceleration geometry appears to make the radiation linearly polarized when observed in the orbital plane, and circularly polarized when observed at a small angle to that plane. Amplitude and frequency are however focused to the polar ecliptic.
Synchrotron radiation may occur in accelerators either as a nuisance, causing undesired energy loss in particle physics contexts, or as a deliberately produced radiation source for numerous laboratory applications. Electrons are accelerated to high speeds in several stages to achieve a final energy that is typically in the GeV range. In the LHC proton bunches also produce the radiation at increasing amplitude and frequency as they accelerate with respect to the vacuum field, propagating photoelectrons, which in turn propagate secondary electrons from the pipe walls with increasing frequency and density up to 7×1010. Each proton may lose 6.7 keV per turn due to this phenomenon.
Synchrotron radiation is also generated by astronomical objects, typically where relativistic electrons spiral (and hence change velocity) through magnetic fields. Two of its characteristics include non-thermal power-law spectra, and polarization.
It was first detected in a jet emitted by Messier 87 in 1956 by Geoffrey R. Burbidge, who saw it as confirmation of a prediction by Iosif S. Shklovsky in 1953, but it had been predicted earlier by Hannes Alfvén and Nicolai Herlofson in 1950. Solar flares accelerate particles that emit in this way, as suggested by R. Giovanelli in 1948 and described critically by J.H. Piddington in 1952.
T. K. Breus noted that questions of priority on the history of astrophysical synchrotron radiation are complicated, writing:
In particular, the Russian physicist V.L. Ginzburg broke his relationships with I.S. Shklovsky and did not speak with him for 18 years. In the West, Thomas Gold and Sir Fred Hoyle were in dispute with H. Alfven and N. Herlofson, while K.O. Kiepenheuer and G. Hutchinson were ignored by them.
Supermassive black holes have been suggested for producing synchrotron radiation, by ejection of jets produced by gravitationally accelerating ions through the super contorted 'tubular' polar areas of magnetic fields. Such jets, the nearest being in Messier 87, have been confirmed by the Hubble telescope as apparently superluminal, travelling at 6 × c (six times the speed of light) from our planetary frame. This phenomenon is caused because the jets are travelling very near the speed of light and at a very small angle towards the observer. Because at every point of their path the high-velocity jets are emitting light, the light they emit does not approach the observer much more quickly than the jet itself. Light emitted over hundreds of years of travel thus arrives at the observer over a much smaller time period (ten or twenty years) giving the illusion of faster than light travel. There is no violation of special relativity.
A class of astronomical sources where synchrotron emission is important is the pulsar wind nebulae, a.k.a. plerions, of which the Crab nebula and its associated pulsar are archetypal. Pulsed emission gamma-ray radiation from the Crab has recently been observed up to ≥25 GeV, probably due to synchrotron emission by electrons trapped in the strong magnetic field around the pulsar. Polarization in the Crab at energies from 0.1 to 1.0 MeV illustrates a typical synchrotron radiation.
We start with the expressions for the Liénard–Wiechert field:
In equation (1), and (2), the first terms for B and E resulting from the particle fall off as the inverse square of the distance from the particle, and this first term is called the generalized Coulomb field or velocity field. These terms represents the particle static field effect, which is a function of the component of its motion that has zero or constant velocity, as seen by a distant observer at r. By contrast, the second terms fall off as the inverse first power of the distance from the source, and these second terms are called the acceleration field or radiation field because they represent components of field due to the charge's acceleration (changing velocity), and they represent E and B which are emitted as electromagnetic radiation from the particle to an observer at r.
If we ignore the velocity field in order to find the power of emitted EM radiation only, the radial component of Poynting's vector resulting from the Liénard–Wiechert fields can be calculated to be
The energy radiated into per solid angle during a finite period of acceleration from t′ = T1 to t′ = T2 is
Integrating Eq. (4) over the all solid angles, we get the relativistic generalization of Larmor's formula
However, this also can be derived by relativistic transformation of the 4-acceleration in Larmor's formula.
When the charge is in instantaneous circular motion, its acceleration is perpendicular to its velocity β→. Choosing a coordinate system such that instantaneously β→ is in the z direction and is in the x direction, with the polar and azimuth angles θ and φ defining the direction of observation, the general formula Eq. (4) reduces to
In the relativistic limit , the angular distribution can be written approximately as
The factors (1 − βcosθ) in the denominators tip the angular distribution forward into a narrow cone like the beam of a headlight pointing ahead of the particle. A plot of the angular distribution (dP/dΩ vs. γθ) shows a sharp peak around θ = 0.
Integration over the whole solid angle yields the total power radiated by one electron
where E is the electron energy, B is the magnetic field, and ρ is the radius of curvature of the track in the field. Note that the radiated power is proportional to 1/, 1/, and B2. In some cases the surfaces of vacuum chambers hit by synchrotron radiation have to be cooled because of the high power of the radiation.
where α is the angle between the velocity and the magnetic field and r is the radius of the circular acceleration, the power emitted is:
Thus the power emitted scales as energy to the fourth, and decreases with the square of the radius and the fourth power of particle mass. This radiation is what limits the energy of an electron-positron circular collider. Generally, proton-proton colliders are instead limited by the maximum magnetic field; this is why, for example, the LHC has a center-of-mass energy 70 times higher than the LEP even though the proton mass is 2000 times the electron mass.
The energy received by an observer (per unit solid angle at the source) is
Using the Fourier transformation we move to the frequency space
Angular and frequency distribution of the energy received by an observer (consider only the radiation field)
Therefore, if we know the particle's motion, cross products term, and phase factor, we could calculate the radiation integral. However, calculations are generally quite lengthy (even for simple cases as for the radiation emitted by an electron in a bending magnet, they require Airy function or the modified Bessel functions).
Trajectory of the arc of circumference is
In the limit of small angles we compute
Substituting into the radiation integral and introducing
where the function K is a modified Bessel function of the second kind.
From Eq.(10), we observe that the radiation intensity is negligible for . Critical frequency is defined as the frequency when ξ = 1/ and θ = 0. So,
and critical angle is defined as the angle for which and is approximately
For frequencies much larger than the critical frequency and angles much larger than the critical angle, the synchrotron radiation emission is negligible.
Integrating on all angles, we get the frequency distribution of the energy radiated.
If we define
where y = ω/. Then
Note that , if , and , if
The formula for spectral distribution of synchrotron radiation, given above, can be expressed in terms of a rapidly converging integral with no special functions involved (see also modified Bessel functions ) by means of the relation:
First, define the critical photon energy as
Then, the relationship between radiated power and photon energy is shown in the graph on the right side. The higher the critical energy, the more photons with high energies are generated. Note that, there is no dependence on the energy at longer wavelength.
In Eq.(10), the first term is the radiation power with polarization in the orbit plane, and the second term is the polarization orthogonal to the orbit plane.
In the orbit plane , the polarization is purely horizontal. Integrating on all frequencies, we get the angular distribution of the energy radiated
Integrating on all the angles, we find that seven times as much energy is radiated with parallel polarization as with perpendicular polarization. The radiation from a relativistically moving charge is very strongly, but not completely, polarized in the plane of motion.
An undulator consists of a periodic array of magnets, so that they provide a sinusoidal magnetic field.
Solution of equation of motion is
and the parameter is called the undulator parameter.
Condition for the constructive interference of radiation emitted at different poles is
Expanding and neglecting the terms in the resulting equation, one obtains
For , one finally gets
This equation is called the undulator equation.
Radiation integral is
Using the periodicity of the trajectory, we can split the radiation integral into a sum over terms, where is the total number of bending magnets of the undulator.
, and , , and
The radiation integral in an undulator can be written as
where is the frequency difference to the n-th harmonic. The sum of δ generates a series of sharp peaks in the frequency spectrum harmonics of fundamental wavelength
and Fn depends on the angles of observations and K
On the axis (θ = 0, φ = 0), the radiation integral becomes
Note that only odd harmonics are radiated on-axis, and as K increases higher harmonic becomes stronger.
The Advanced Photon Source (APS) at Argonne National Laboratory (in Argonne, Illinois, USA) is a national synchrotron-radiation light source research facility funded by the United States Department of Energy Office of Science. The facility "saw first light" on March 26, 1995. Argonne National Laboratory is managed by UChicago Argonne LLC, which is composed of the University of Chicago and Jacobs Engineering Group.
Using high-brilliance X-ray beams from the APS, members of the international synchrotron-radiation research community conduct forefront basic and applied research in the fields of materials science and biological science; physics and chemistry; environmental, geophysical and planetary science; and innovative X-ray instrumentation. As of 2015, APS held the distinction of being the facility at which 21 of the 30 known g-protein coupled receptor protein structures had been solved.CANDLE Synchrotron Research Institute
Officially the Center for the Advancement of Natural Discoveries using Light Emission, more commonly CANDLE Synchrotron Research Institute, is a project and a research center-institute in Yerevan, Armenia. CANDLE is a project of 3 gigaelectronvolts energy, third generation synchrotron light source for fundamental, industrial and applied research in biology, physics, chemistry, medicine, material and environmental sciences.
Overall the facility is expected to serve more than 40 research groups simultaneously supporting the spectroscopy, scattering, imaging and time resolved experiments.
The project is claimed to be demanded by international scientific community and is expected to have a vast impact on development of science in Armenia.The government of Armenia allocated an area of 20 ha near the town of Abovyan for the upcoming projects of the center.Cornell Laboratory for Accelerator-based Sciences and Education
The Cornell Laboratory for Accelerator-based Sciences and Education (CLASSE) is a particle accelerator facility located in Wilson Laboratory on the Cornell University campus in Ithaca, NY. CLASSE formed from the merger of the Cornell High-Energy Synchrotron Source (CHESS) and the Laboratory for Elementary-Particle Physics (LEPP) in July 2006. Ritchie Patterson is the Director of CLASSE.
The Wilson Synchrotron Lab, which houses both the Cornell Electron Storage Ring (CESR) and CHESS, is named after Robert R. Wilson, known for his work as a group leader in the Manhattan Project, for being the first director of the Fermi National Accelerator Laboratory, and for contributing to the design of CESR.DESY
The Deutsches Elektronen-Synchrotron (English German Electron Synchrotron) commonly referred to by the abbreviation DESY, is a national research center in Germany that operates particle accelerators used to investigate the structure of matter. It conducts a broad spectrum of inter-disciplinary scientific research in three main areas: particle and high energy physics; photon science; and the development, construction and operation of particle accelerators. Its name refers to its first project, an electron synchrotron. DESY is publicly financed by the Federal Republic of Germany, the States of Germany, and the German Research Foundation (DFG). DESY is a member of the Helmholtz Association and operates at sites in Hamburg and Zeuthen.Daresbury Laboratory
Daresbury Laboratory is a scientific research laboratory based at Sci-Tech Daresbury campus near Daresbury in Halton, Cheshire, England. The laboratory began operations in 1962 and was officially opened on 16 June 1967 as the Daresbury Nuclear Physics Laboratory by the then Prime Minister of United Kingdom, Harold Wilson. It is operated by the Science and Technology Facilities Council, part of UK Research and Innovation. It currently employs around 300 staff. The current director is Prof. Susan Smith.European Synchrotron Radiation Facility
The European Synchrotron Radiation Facility (ESRF) is a joint research facility situated in Grenoble, France, and supported by 22 countries (13 member countries: France, Germany, Italy, UK, Spain, Switzerland, Belgium, The Netherlands, Denmark, Finland, Norway, Sweden, Russia and 9 associate countries: Austria, Portugal, Israel, Poland, Czech Republic, Hungary, Slovakia, India and South Africa).Some 8,000 scientists visit this particle accelerator each year, conducting upwards of 2,000 experiments and producing around 1,800 scientific publications.Kurchatov Center for Synchrotron Radiation and Nanotechnology
The Kurchatov Center for Synchrotron Radiation and Nanotechnology (KCSRN) is a Russian interdisciplinary institute for synchrotron-based research. The source is used for research in fields such as biology, chemistry, physics and palaeontology.As with all synchrotron sources, the Kurchatov source is a user facility.List of synchrotron radiation facilities
This is a table of synchrotrons and storage rings used as synchrotron radiation sources, and free electron lasers.NGC 383
NGC 383 is a double radio galaxy with a quasar-like appearance located in the constellation Pisces. It is listed in Halton C. Arp's 1966 "The Arp Atlas of Peculiar Galaxies." Recent discoveries by the National Radio Astronomy Observatory in 2006 reveal that NGC 383 is being bisected by high energy relativistic electrons traveling at relatively high fractions of the speed of light. These relativistic electrons are detected as synchrotron radiation in the x-ray and radio wavelengths. The focus of this intense energy is the galactic center of NGC 383. The relativistic electron jets detected as synchrotron radiation extend for several thousand parsecs and then appear to dissipate at the ends in the form of streamers or filaments.
There are four other nearby galaxies NGC 379, NGC 380, NGC 385, and NGC 384 which are suspected of being closely associated with NGC 383, as well as several other galaxies at relatively close distance.
A Type 1a supernova, SN 2015ar, was discovered in NGC 383 in November 2015.National Synchrotron Light Source
The National Synchrotron Light Source (NSLS) at Brookhaven National Laboratory (BNL) in Upton, New York is a national user research facility funded by the U.S. Department of Energy (DOE). Built from 1978 through 1984, and officially shut down on September 30, 2014, the NSLS was considered a second-generation synchrotron.The NSLS experimental floor consists of two electron storage rings: an X-ray ring and a VUV (vacuum ultraviolet) ring which provide intense, focused light spanning the electromagnetic spectrum from the infrared through X-rays. The properties of this light and the specially designed experimental stations, called beamlines, allow scientists in many fields of research to perform experiments not otherwise possible at their own laboratories.Positron-Electron Tandem Ring Accelerator
The Positron-Electron Tandem Ring Accelerator (PETRA) is one of the particle accelerators at DESY in Hamburg, Germany. From 1978 to 1986 it was used to study electron–positron collisions. It was here that the TASSO collaboration found the first direct evidence for gluons in three jet events. The modification called PETRA-II is a source of high-energy synchrotron radiation and also a pre-accelerator for the HERA. Started in 2007, an upgrade has been converting it to PETRA-III, which is a high intensity source for synchrotron radiation.SLAC National Accelerator Laboratory
SLAC National Accelerator Laboratory, originally named Stanford Linear Accelerator Center, is a United States Department of Energy National Laboratory operated by Stanford University under the programmatic direction of the U.S. Department of Energy Office of Science and located in Menlo Park, California.
SLAC research centers on a broad program in atomic and solid-state physics, chemistry, biology, and medicine using X-rays from synchrotron radiation and a free-electron laser as well as experimental and theoretical research in elementary particle physics, astroparticle physics, and cosmology.SPring-8
SPring-8 (an acronym of Super Photon Ring – 8 GeV) is a synchrotron radiation facility located in Hyōgo Prefecture, Japan, which was developed jointly by RIKEN and the Japan Atomic Energy Research Institute. It is owned and managed by RIKEN, and run under commission by the Japan Synchrotron Radiation Research Institute. The machine consists of a storage ring containing an 8 GeV electron beam. On its path around the storage ring, the beam passes through insertion devices to produce synchrotron radiation with energies ranging from soft X-rays (300 eV) up to hard X-rays (300 keV). The synchrotron radiation produced at SPring-8 is used for materials analysis and biochemical protein characterization by many Japanese manufacturers and universities.
Together with the Advanced Photon Source at Argonne National Laboratory and the Cornell High Energy Synchrotron Source at Cornell University in the United States, the European Synchrotron Radiation Facility in Grenoble, France and PETRA at DESY in Hamburg, Germany, it is one of the five large (beam energy greater than 5 GeV) synchrotron radiation facilities in the world.Sokolov–Ternov effect
The Sokolov–Ternov effect is the effect of self-polarization of relativistic electrons or positrons moving at high energy in a magnetic field. The self-polarization occurs through the emission of spin-flip synchrotron radiation. The effect was predicted by Igor Ternov and the prediction rigorously justified by Arseny Sokolov using exact solutions to the Dirac equation.Stanford Synchrotron Radiation Lightsource
The Stanford Synchrotron Radiation Lightsource (formerly Stanford Synchrotron Radiation Laboratory), a division of SLAC National Accelerator Laboratory, is operated by Stanford University for the Department of Energy. SSRL is a National User Facility which provides synchrotron radiation, a name given to electromagnetic radiation in the x-ray, ultraviolet, visible and infrared realms produced by electrons circulating in a storage ring (Stanford Positron Electron Asymmetric Ring - SPEAR) at nearly the speed of light. The extremely bright light that is produced can be used to investigate various forms of matter ranging from objects of atomic and molecular size to man-made materials with unusual properties. The obtained information and knowledge is of great value to society, with impact in areas such as the environment, future technologies, health, and education.The SSRL provides experimental facilities to some 2,000 academic and industrial scientists working in such varied fields as drug design, environmental cleanup, electronics, and x-ray imaging. It is located in southern San Mateo County, just outside the city of Menlo Park.Storage ring
A storage ring is a type of circular particle accelerator in which a continuous or pulsed particle beam may be kept circulating typically for many hours. Storage of a particular particle depends upon the mass, momentum and usually the charge of the particle to be stored. Storage rings most commonly store electrons, positrons, or protons.
Storage rings are most often used to store electrons that radiate synchrotron radiation. Over 50 facilities based on electron storage rings exist and are used for a variety of studies in chemistry and biology. Storage rings can also be used to produce polarized high-energy electron beams through the Sokolov-Ternov effect. The best-known application of storage rings is their use in particle accelerators and in particle colliders, where two counter-rotating beams of stored particles are brought into collision at discrete locations. The resulting subatomic interactions are then studied in a surrounding particle detector. Examples of such facilities are LHC, LEP, PEP-II, KEKB, RHIC, Tevatron and HERA.
A storage ring is a type of synchrotron. While a conventional synchrotron serves to accelerate particles from a low to a high energy state with the aid of radio-frequency accelerating cavities, a storage ring keeps particles stored at a constant energy and radio-frequency cavities are only used to replace energy lost through synchrotron radiation and other processes.
Gerard K. O'Neill proposed the use of storage rings as building blocks for a collider in 1956. A key benefit of storage rings in this context is that the storage ring can accumulate a high beam flux from an injection accelerator that achieves a much lower flux.Synchrotron Radiation Center
The Synchrotron Radiation Center (SRC), located in Stoughton, Wisconsin and operated by the University of Wisconsin–Madison, was a national synchrotron light source research facility, operating the Aladdin storage ring. From 1968 to 1987 SRC was the home of Tantalus, the first storage ring dedicated to the production of synchrotron radiation.Synchrotron Radiation Source
The Synchrotron Radiation Source (SRS) at the Daresbury Laboratory in Cheshire, England was the first second-generation synchrotron radiation source to produce X-rays. The research facility provided synchrotron radiation to a large number of experimental stations and had an operating cost of approximately £20 million per annum.SRS had been operated by the Science and Technology Facilities Council. The SRS was closed on 4 August 2008 after 28 years of operation.Synchrotron light source
A synchrotron light source is a source of electromagnetic radiation (EM) usually produced by a storage ring, for scientific and technical purposes. First observed in synchrotrons, synchrotron light is now produced by storage rings and other specialized particle accelerators, typically accelerating electrons. Once the high-energy electron beam has been generated, it is directed into auxiliary components such as bending magnets and insertion devices (undulators or wigglers) in storage rings and free electron lasers.
These supply the strong magnetic fields perpendicular to the beam which are needed to convert high energy electrons into photons.
The major applications of synchrotron light are in condensed matter physics, materials science, biology and medicine. A large fraction of experiments using synchrotron light involve probing the structure of matter from the sub-nanometer level of electronic structure to the micrometer and millimeter level important in medical imaging. An example of a practical industrial application is the manufacturing of microstructures by the LIGA process.