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**Synchrotron radiation** (also known as **magnetobremsstrahlung radiation**) is the electromagnetic radiation emitted when charged particles are accelerated radially, e.g., 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.^{ [1] } 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.

* Bremsstrahlung*, from

In physics, **electromagnetic radiation** refers to the waves of the electromagnetic field, propagating (radiating) through space, carrying electromagnetic radiant energy. It includes radio waves, microwaves, infrared, (visible) light, ultraviolet, X-rays, and gamma rays.

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 which bends the particle beam into its closed path increases with time during the accelerating process, being *synchronized* to the increasing kinetic energy 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 27-kilometre-circumference (17 mi) Large Hadron Collider (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 teraelectronvolts (TeV).

- History
- Properties of synchrotron radiation
- Emission mechanism
- Synchrotron radiation from accelerators
- Synchrotron radiation in astronomy
- History of detection
- Pulsar wind nebulae
- Formulation
- Liénard–Wiechert Field
- Velocity perpendicular to acceleration (v ⟂ a): synchrotron radiation
- Radiation integral
- Example 1: bending magnet
- Example 2: undulator
- See also
- Notes
- References
- External links

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".^{ [2] } Pollock recounts:

**General Electric Company** (**GE**) is an American multinational conglomerate incorporated in New York City and headquartered in Boston. As of 2018, the company operates through the following segments: aviation, healthcare, power, renewable energy, digital industry, additive manufacturing, venture capital and finance, lighting, and oil and gas.

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.

^{ [3] }

Cherenkov radiationis electromagnetic radiation emitted when a charged particle passes through a dielectric medium at a speed greater than the phase velocity of light in that medium. The characteristic blue glow of an underwater nuclear reactor is due to Cherenkov radiation. It is named for Soviet physicist Pavel Cherenkov, who shared the 1958 Nobel Prize in Physics for its discovery.

Dmitri Dmitrievich Ivanenkowas a Soviet-Ukrainian theoretical physicist who made great contributions to the physical science of the twentieth century, especially to nuclear physics, field theory, and gravitation theory. He worked in the Poltava Gravimetric Observatory of the Institute of Geophysics of NAS of Ukraine, was the head of the Theoretical Department Ukrainian Physico-Technical Institute in Kharkiv, Head of the Department of Theoretical Physics of the Kharkiv Institute of Mechanical Engineering. Professor of University of Kharkiv, Professor of Moscow State University.

Isaak Yakovlevich Pomeranchukwas a Soviet theoretical physicist working in particle physics, quantum field theory, electromagnetic and synchrotron radiation, condensed matter physics and the physics of liquid helium. The Pomeranchuk instability, the pomeron, and a few other phenomena in particle and condensed matter physics are named after him.

- Broad Spectrum (which covers from microwaves to hard X-rays): the users can select the wavelength required for their experiment;
- High Flux: high intensity photon beam allows rapid experiments or use of weakly scattering crystals;
- High Brilliance: highly collimated photon beam generated by a small divergence and small size source (spatial coherence);
- High Stability: submicron source stability;
- Polarization: both linear and circular;
- Pulsed Time Structure: pulsed length down to tens of picoseconds allows the resolution of process on the same time scale.

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.

A **magnetic field** is a vector field that describes the magnetic influence of electric charges in relative motion and magnetized materials. The effects of magnetic fields are commonly seen in permanent magnets, which pull on magnetic materials and attract or repel other magnets. Magnetic fields surround and are created by magnetized material and by moving electric charges such as those used in electromagnets. They exert forces on nearby moving electrical charges and torques on nearby magnets. In addition, a magnetic field that varies with location exerts a force on magnetic materials. Both the strength and direction of a magnetic field vary with location. As such, it is described mathematically as a vector field.

**Relativistic speed** refers to speed at which relativistic effects become significant to the desired accuracy of measurement of the phenomenon being observed. Relativistic effects are those discrepancies between values calculated by models considering and not considering relativity. Related words are velocity, rapidity, and celerity which is proper velocity. Speed is a scalar, being the magnitude of the velocity vector which in relativity is the four-velocity and in three-dimension Euclidean space a three-velocity. Speed is empirically measured as average speed, although current devices in common use can estimate speed over very small intervals and closely approximate instantaneous speed. Non-relativistic discrepancies include cosine error which occurs in speed detection devices when only one scalar component of the three-velocity is measured and the Doppler effect which may affect observations of wavelength and frequency9.

The **Doppler effect** is the change in frequency or wavelength of a wave in relation to an observer who is moving relative to the wave source. It is named after the Austrian physicist Christian Doppler, who described the phenomenon in 1842.

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 7×10^{10}. Each proton may lose 6.7 keV per turn due to this phenomenon.^{ [4] }

**Particle physics** is a branch of physics that studies the nature of the particles that constitute matter and radiation. Although the word *particle* can refer to various types of very small objects, *particle physics* usually investigates the irreducibly smallest detectable particles and the fundamental interactions necessary to explain their behaviour. By our current understanding, these elementary particles are excitations of the quantum fields that also govern their interactions. The currently dominant theory explaining these fundamental particles and fields, along with their dynamics, is called the Standard Model. Thus, modern particle physics generally investigates the Standard Model and its various possible extensions, e.g. to the newest "known" particle, the Higgs boson, or even to the oldest known force field, gravity.

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 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 **Large Hadron Collider** (**LHC**) is the world's largest and most powerful particle collider and the largest machine in the world. It was built by the European Organization for Nuclear Research (CERN) between 1998 and 2008 in collaboration with over 10,000 scientists and hundreds of universities and laboratories, as well as more than 100 countries. It lies in a tunnel 27 kilometres (17 mi) in circumference and as deep as 175 metres (574 ft) beneath the France–Switzerland border near Geneva.

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.^{ [5] }

It was first detected in a jet emitted by Messier 87 in 1956 by Geoffrey R. Burbidge,^{ [6] } 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^{ [7] } 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.^{ [8] }

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.

^{ [9] }

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.^{ [10] }

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,^{ [11] } probably due to synchrotron emission by electrons trapped in the strong magnetic field around the pulsar. Polarization in the Crab^{ [12] } at energies from 0.1 to 1.0 MeV illustrates a typical synchrotron radiation.

We start with the expressions for the Liénard–Wiechert field of a point charge of mass and charge :

where **R**(*t*′) = **r**−**r**_{0}(*t*′), *R*(*t*′) = |**R**(*t*′)|, and **n**(*t*′) = **R**(*t*′)/*R*(*t*′), which is the unit vector between the observation point and the position of the charge at the retarded time, and *t*′ is the retarded time.

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

Note that

- The spatial relationship between
*β*→ and determines the detailed angular power distribution. - The relativistic effect of transforming from the rest frame of the particle to the observer's frame manifests itself by the presence of the factors (1 −
*β*→⋅**n̂**) in the denominator of Eq. (3). - For ultrarelativistic particles the latter effect dominates the whole angular distribution.

The energy radiated into per solid angle during a finite period of acceleration from *t*′ = *T*_{1} to *t*′ = *T*_{2} 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 −*β*cos*θ*) 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 (d*P*/d*Ω* vs. *γθ*) shows a sharp peak around *θ* = 0.

If we neglect any electric force on the particle, the total power radiated (over all solid angle) from Eq. (4) is

where *E* is the particle's total (kinetic plus rest) 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/*m*^{4}, 1/*ρ*^{2}, and *B*^{2}. In some cases the surfaces of vacuum chambers hit by synchrotron radiation have to be cooled because of the high power of the radiation.

Using

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* = 1/2 and *θ* = 0. So,

and *critical angle* is defined as the angle for which and is approximately

^{ [13] }

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*/*ω*_{c}. 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^{ [14] } (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

where

and

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.

where

, 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 *F*_{n} depends on the angles of observations and *K*

On the axis (*θ* = 0, *φ* = 0), the radiation integral becomes

and

where

Note that only odd harmonics are radiated on-axis, and as *K* increases higher harmonic becomes stronger.

- ↑ Yale Astronomy http://www.astro.yale.edu/vdbosch/astro320_summary27.pdf
- ↑ Elder, F. R.; Gurewitsch, A. M.; Langmuir, R. V.; Pollock, H. C., "Radiation from Electrons in a Synchrotron" (1947)
*Physical Review*, vol. 71, Issue 11, pp. 829-830 - ↑ Iwanenko D., Pomeranchuk I., "On the maximal energy attainable in betatron", (1944)
*Physical Review*vol.65, p. 343 - ↑ Synchrotron Radiation Damping in the LHC 2005 Joachim Tuckmantel.
- ↑ Vladimir A. Bordovitsyn, "Synchrotron Radiation in Astrophysics" (1999)
*Synchrotron Radiation Theory and Its Development*, ISBN 981-02-3156-3 - ↑ Burbidge, G. R. "On Synchrotron Radiation from Messier 87.
*Astrophysical Journal*, vol. 124, p. 416" - ↑ Alfvén, H.; Herlofson, N. "Cosmic Radiation and Radio Stars"
*Physical Review*(1950), vol. 78, Issue 5, pp. 616–616 - ↑ Paddington, J.H., "Thermal Theories of the High-Intensity Component of Solar Radio-Frequency Radiation. (1952)
*Proceedings of the Physical Society. Section B*, vol.**66**, Number 2 - ↑ Breus, T. K., "Istoriya prioritetov sinkhrotronnoj kontseptsii v astronomii %t (Historical problems of the priority questions of the synchrotron concept in astrophysics)" (2001) in
*Istoriko-Astronomicheskie Issledovaniya*, Vyp. 26, p. 88 – 97, 262 (2001) - ↑ Chase, Scott I. "Apparent Superluminal Velocity of Galaxies" . Retrieved 22 August 2012.
- ↑ "Observation of Pulsed {gamma}-Rays Above 25 GeV from the Crab Pulsar with MAGIC",
*Science*21 November 2008: Vol. 322. no. 5905, pp. 1221–1224" - ↑
*Dean et al.*,"Polarized Gamma-Ray Emission from the Crab",*Science*29 August 2008: Vol. 321. no. 5893, pp. 1183–1185 - ↑ Jackson, John David (1999).
*Classical Electrodynamics*(3rd ed.). Chichester: Wiley. p. 680. ISBN 978-0-471-30932-1. - ↑ M.Kh.Khokonov. Cascade Processes of Energy Loss by Emission of Hard Photons // JETP, V.99, No.4, pp. 690-707 \ (2004).

In mathematics, the **winding number** of a closed curve in the plane around a given point is an integer representing the total number of times that curve travels counterclockwise around the point. The winding number depends on the orientation of the curve, and is negative if the curve travels around the point clockwise.

In geometry, a **solid angle** is a measure of the amount of the field of view from some particular point that a given object covers. That is, it is a measure of how large the object appears to an observer looking from that point. The point from which the object is viewed is called the *apex* of the solid angle, and the object is said to *subtend* its solid angle from that point.

In mechanics and geometry, the **3D rotation group**, often denoted **SO(3)**, is the group of all rotations about the origin of three-dimensional Euclidean space **R**^{3} under the operation of composition. By definition, a rotation about the origin is a transformation that preserves the origin, Euclidean distance, and orientation. Every non-trivial rotation is determined by its axis of rotation and its angle of rotation. Composing two rotations results in another rotation; every rotation has a unique inverse rotation; and the identity map satisfies the definition of a rotation. Owing to the above properties, the set of all rotations is a group under composition. Rotations are not commutative, making it a nonabelian group. Moreover, the rotation group has a natural structure as a manifold for which the group operations are smoothly differentiable; so it is in fact a Lie group. It is compact and has dimension 3.

In physics, a **wave vector** is a vector which helps describe a wave. Like any vector, it has a magnitude and direction, both of which are important. Its magnitude is either the wavenumber or angular wavenumber of the wave, and its direction is ordinarily the direction of wave propagation.

In mathematics, and specifically differential geometry, a **connection form** is a manner of organizing the data of a connection using the language of moving frames and differential forms.

In mathematics, the **Hamilton–Jacobi equation** (**HJE**) is a necessary condition describing extremal geometry in generalizations of problems from the calculus of variations, and is a special case of the Hamilton–Jacobi–Bellman equation. It is named for William Rowan Hamilton and Carl Gustav Jacob Jacobi.

The **rigid rotor** is a mechanical model of rotating systems. An arbitrary rigid rotor is a 3-dimensional rigid object, such as a top. To orient such an object in space requires three angles, known as Euler angles. A special rigid rotor is the *linear rotor* requiring only two angles to describe, for example of a diatomic molecule. More general molecules are 3-dimensional, such as water, ammonia, or methane.

The **Havriliak–Negami relaxation** is an empirical modification of the Debye relaxation model in electromagnetism. Unlike the Debye model, the Havriliak–Negami relaxation accounts for the asymmetry and broadness of the dielectric dispersion curve. The model was first used to describe the dielectric relaxation of some polymers, by adding two exponential parameters to the Debye equation:

The **Larmor formula** is used to calculate the total power radiated by a non relativistic point charge as it accelerates. This is used in the branch of physics known as electrodynamics and is not to be confused with the Larmor precession from classical nuclear magnetic resonance. It was first derived by J. J. Larmor in 1897, in the context of the wave theory of light.

A **theoretical motivation for general relativity**, including the motivation for the geodesic equation and the Einstein field equation, can be obtained from special relativity by examining the dynamics of particles in circular orbits about the earth. A key advantage in examining circular orbits is that it is possible to know the solution of the Einstein Field Equation *a priori*. This provides a means to inform and verify the formalism.

A **quasiprobability distribution** is a mathematical object similar to a probability distribution but which relaxes some of Kolmogorov's axioms of probability theory. Although quasiprobabilities share several of general features with ordinary probabilities, such as, crucially, *the ability to yield expectation values with respect to the weights of the distribution*, they all violate the *σ*-additivity axiom, because regions integrated under them do not represent probabilities of mutually exclusive states. To compensate, some quasiprobability distributions also counterintuitively have regions of negative probability density, contradicting the first axiom. Quasiprobability distributions arise naturally in the study of quantum mechanics when treated in phase space formulation, commonly used in quantum optics, time-frequency analysis, and elsewhere.

The **Frank–Tamm formula** yields the amount of Cherenkov radiation emitted on a given frequency as a charged particle moves through a medium at superluminal velocity. It is named for Russian physicists Ilya Frank and Igor Tamm who developed the theory of the Cherenkov effect in 1937, for which they were awarded a Nobel Prize in Physics in 1958.

In mathematics, the **Schur orthogonality relations**, which is proven by Issai Schur through Schur's lemma, express a central fact about representations of finite groups. They admit a generalization to the case of compact groups in general, and in particular compact Lie groups, such as the rotation group SO(3).

A **biarc** is a smooth curve formed from two circular arcs. In order to make the biarc smooth, the two arcs should have the same tangent at the connecting point where they meet.

In general relativity, a point mass deflects a light ray with impact parameter by an angle approximately equal to

In physics, **Berry connection** and **Berry curvature** are related concepts which can be viewed, respectively, as a local gauge potential and gauge field associated with the Berry phase or geometric phase. These concepts were introduced by Michael Berry in a paper published in 1984 emphasizing how geometric phases provide a powerful unifying concept in several branches of classical and quantum physics.

The **table of chords**, created by the Greek astronomer, geometer, and geographer Ptolemy in Egypt during the 2nd century AD, is a trigonometric table in Book I, chapter 11 of Ptolemy's *Almagest*, a treatise on mathematical astronomy. It is essentially equivalent to a table of values of the sine function. It was the earliest trigonometric table extensive enough for many practical purposes, including those of astronomy. Centuries passed before more extensive trigonometric tables were created. One such table is the *Canon Sinuum* created at the end of the 16th century.

**Multipole radiation** is a theoretical framework for the description of electromagnetic or gravitational radiation from time-dependent distributions of distant sources. These tools are applied to physical phenomena which occur at a variety of length scales - from gravitational waves due to galaxy collisions to gamma radiation resulting from nuclear decay. Multipole radiation is analyzed using similar multipole expansion techniques that describe fields from static sources, however there are important differences in the details of the analysis because multipole radiation fields behave quite differently from static fields. This article is primarily concerned with electromagnetic multipole radiation, although the treatment of gravitational waves is similar.

**Elementary flow** is a collection of basic flows from which is possible to construct more complex flows by superposition. Some of the flows reflect specific cases and constraints such as incompressible, irrotational or both as in the case of Potential flow.

- Brau, Charles A. Modern Problems in Classical Electrodynamics. Oxford University Press, 2004. ISBN 0-19-514665-4.
- Jackson, John David. Classical Electrodynamics. John Wiley & Sons, 1999. ISBN 0-471-30932-X
- Ishfaq Ahmad, D.Sc. "Measurements of the Relative Oscillator Strengths using the Synchrotron Radiation" (PDF).
*Proceedings of the National Syposium on Frontier of Physics, National Centre for Theoretical Physics*. Pakistan Physical Society. Retrieved 16 January 2012.

- Cosmic Magnetobremsstrahlung (synchrotron Radiation), by Ginzburg, V. L., Syrovatskii, S. I., ARAA, 1965
- Developments in the Theory of Synchrotron Radiation and its Reabsorption, by Ginzburg, V. L., Syrovatskii, S. I., ARAA, 1969
- Lightsources.org
- BioSync – a structural biologist's resource for high energy data collection facilities
- X-Ray Data Booklet

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