synchrotron radiation

シンクロトロン放射光

WordNet

1. the spontaneous emission of a stream of particles or electromagnetic rays in nuclear decay (同)radioactivity
2. energy that is radiated or transmitted in the form of rays or waves or particles
3. the act of spreading outward from a central source
4. a radial arrangement of nerve fibers connecting different parts of the brain
5. the spread of a group of organisms into new habitats
6. cyclotron in which the electric field is maintained at a constant frequency

PrepTutorEJDIC

1. 〈U〉(光・熱・放射能などの)発散,放射 / 〈C〉放射物;放射線;輻射(ふくしゃ)熱 / 〈C〉(喜び・幸福感などの)発散《+『of』+『名』》 / =radioactivity
2. シンクロトロン(電子加速装置)

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出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2017/04/16 19:06:14」(JST)

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This article is about physical phenomenon of synchrotron radiation. For details on the production of this radiation and applications in laboratories, see Synchrotron light source.

Synchrotron 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.

Synchrotron radiation from a bending magnet

Synchrotron radiation from an undulator

History

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.

Properties of synchrotron radiation

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

Emission mechanism

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 in the lab 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 from accelerators

Main article: Synchrotron light source

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 in astronomy

Messier 87's Energetic Jet, HST image. The blue light from the jet emerging from the bright AGN core, towards the lower right, is due to synchrotron radiation.

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.

History of detection

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 is 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.

Crab Nebula. The bluish glow from the central region of the nebula is due to synchrotron radiation.

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.

Pulsar wind nebulae

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.

Formulation

Liénard–Wiechert Field

We start with the expressions for the Liénard–Wiechert field:

${\begin{aligned}\mathbf {B} (\mathbf {r} ,t)&=-{\frac {\mu _{0}q}{4\pi }}\left[{\frac {c\,{\hat {\mathbf {n} }}\times {\vec {\beta }}}{\gamma ^{2}R^{2}\,(1-{\vec {\beta }}\mathbf {\cdot } {\hat {\mathbf {n} }})^{3}}}+{\frac {{\hat {\mathbf {n} }}\times [\,{\dot {\vec {\beta }}}+{\hat {\mathbf {n} }}\times ({\vec {\beta }}\times {\dot {\vec {\beta }}})]}{R\,(1-{\vec {\beta }}\mathbf {\cdot } {\hat {\mathbf {n} }})^{3}}}\right]_{\mathrm {retarded} },\qquad &(1)\\\mathbf {E} (\mathbf {r} ,t)&={\frac {q}{4\pi \varepsilon _{0}}}\left[{\frac {{\hat {\mathbf {n} }}-{\vec {\beta }}}{\gamma ^{2}R^{2}\,(1-{\vec {\beta }}\mathbf {\cdot } {\hat {\mathbf {n} }})^{3}}}+{\frac {{\hat {\mathbf {n} }}\times [({\hat {\mathbf {n} }}-{\vec {\beta }})\times {\dot {\vec {\beta }}}\,]}{c\,R\,(1-{\vec {\beta }}\mathbf {\cdot } {\hat {\mathbf {n} }})^{3}}}\right]_{\mathrm {retarded} },\qquad &(2)\end{aligned}}$

where R(t′) = r − r₀(t′), R(t′) = |R(t′)|, and n̂(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 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. And the second terms fall off as the inverse first power of the distance from the source, and it is called the radiation field or acceleration field.

If we ignore the velocity field, the radial component of Poynting's Vector resulted from the Liénard–Wiechert field can be calculated to be

$[\mathbf {S\cdot } {\hat {\mathbf {n} }}]={\frac {q^{2}}{16\pi ^{2}\varepsilon _{0}c}}\left\{{\frac {1}{R^{2}}}\left|{\frac {{\hat {\mathbf {n} }}\times [({\hat {\mathbf {n} }}-{\vec {\beta }})\times {\dot {\vec {\beta }}}]}{(1-{\vec {\beta }}\mathbf {\cdot } {\hat {\mathbf {n} }})^{3}}}\right|^{2}\right\}_{\text{retarded}}.\qquad \qquad (3)$

Note that

• The spatial relationship between β→ and .→β 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′ = T₁ to t′ = T₂ is

${\begin{aligned}{\frac {\mathrm {d} P}{\mathrm {d} {\mathit {\Omega }}}}&=R(t')^{2}\,[\mathbf {S} (t')\mathbf {\cdot } {\hat {\mathbf {n} }}(t')]\,{\frac {\mathrm {d} t}{\mathrm {d} t'}}=R(t')^{2}\,\mathbf {S} (t')\mathbf {\cdot } {\hat {\mathbf {n} }}(t')\,[1-{\vec {\beta }}(t')\mathbf {\cdot } {\hat {\mathbf {n} }}(t')]\\&={\frac {q^{2}}{16\pi ^{2}\varepsilon _{0}c}}\,{\frac {|{\hat {\mathbf {n} }}(t')\times \{[{\hat {\mathbf {n} }}(t')-{\vec {\beta }}(t')]\times {\dot {\vec {\beta }}}(t')\}|^{2}}{[1-{\vec {\beta }}(t')\mathbf {\cdot } {\vec {\mathbf {n} }}(t')]^{5}}}.\qquad \qquad (4)\end{aligned}}$

Integrating Eq. (4) over the all solid angles, we get relativistic generalization of Larmor's formula

$P={\frac {e^{2}}{6\pi \varepsilon _{0}c}}\gamma ^{6}\left[\left|{\dot {\vec {\beta }}}\right|^{2}-\left|{\vec {\beta }}\times {\dot {\vec {\beta }}}\right|^{2}\right].\qquad (5)$

However, this also can be derived by relativistic transformation of the 4-acceleration in Larmor's formula.

Velocity ⊥ acceleration: synchrotron radiation

When the electron velocity approaches the speed of light, the emission pattern is sharply collimated forward.

When the charge is in instantaneous circular motion, its acceleration .→β is perpendicular to its velocity β→. Choosing a coordinate system such that instantaneously β→ is in the z direction and .→β 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

${\frac {\mathrm {d} P}{\mathrm {d} {\mathit {\Omega }}}}={\frac {q^{2}}{16\pi ^{2}\epsilon _{0}c}}{\frac {|{\dot {\vec {\beta }}}|^{2}}{(1-\beta \cos \theta )^{3}}}\left[1-{\frac {\sin ^{2}\theta \cos ^{2}\phi }{\gamma ^{2}(1-\beta \cos \theta )^{2}}}\right].\qquad (6)$

In the relativistic limit $(\gamma \gg 1)$, the angular distribution can be written approximately as

${\frac {\mathrm {d} P}{\mathrm {d} {\mathit {\Omega }}}}\simeq {\frac {2}{\pi }}{\frac {e^{2}}{c^{3}}}\gamma ^{6}{\frac {|{\dot {\mathbf {v} }}|^{2}}{(1+\gamma ^{2}\theta ^{2})^{3}}}\left[1-{\frac {4\gamma ^{2}\theta ^{2}\cos ^{2}\phi }{(1+\gamma ^{2}\theta ^{2})^{2}}}\right].\qquad \qquad (7)$

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

$P={\frac {e^{2}}{6\pi \epsilon _{0}c}}\left|{\dot {\vec {\beta }}}\right|^{2}\gamma ^{4}={\frac {e^{2}c}{6\pi \epsilon _{0}}}{\frac {\beta ^{4}\gamma ^{4}}{\rho ^{2}}}={\frac {e^{4}}{6\pi \epsilon _{0}m^{4}c^{5}}}E^{2}B^{2},\qquad (8)$

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/m⁴, 1/ρ², 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.

Using

$B={\frac {E\beta }{e\,r\sin(\alpha )}},$

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:

$P={\frac {e^{2}}{6\pi \epsilon _{0}m^{4}c^{5}r^{2}\sin ^{2}(\alpha )}}E^{4}\beta ^{2}.$

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.

Radiation integral

The energy received by an observer (per unit solid angle at the source) is

${\frac {d^{2}W}{d\Omega }}=\int _{-\infty }^{\infty }{\frac {d^{2}P}{d\Omega }}dt=c\varepsilon _{0}\int _{-\infty }^{\infty }\left|R{\vec {E}}(t)\right|^{2}dt$

Using the Fourier transformation we move to the frequency space

${\frac {d^{2}W}{d\Omega }}=2c\varepsilon _{0}\int _{0}^{\infty }\left|R{\vec {E}}(\omega )\right|^{2}d\omega$

Angular and frequency distribution of the energy received by an observer (consider only the radiation field)

${\frac {d^{3}W}{d\Omega d\omega }}=2c\varepsilon _{0}R^{2}\left|{\vec {E}}(\omega )\right|^{2}={\frac {e^{2}}{4\pi \varepsilon _{0}4\pi ^{2}c}}\left|\int _{-\infty }^{\infty }{\frac {{\hat {n}}\times \left[\left({\hat {n}}-{\vec {\beta }}\right)\times {\dot {\vec {\beta }}}\right]}{\left(1-{\hat {n}}\cdot {\vec {\beta }}\right)^{2}}}e^{i\omega (t-{\hat {n}}\cdot {\vec {r}}(t)/c)}dt\right|^{2}.\qquad (9)$

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).

Example 1: bending magnet

Integrating

Trajectory of the arc of circumference

Trajectory of the arc of circumference is

${\vec {r}}(t)=\left(\rho \sin {\frac {\beta c}{\rho }}t,\rho \left(1-\cos {\frac {\beta c}{\rho }}t\right),0\right).$

In the limit of small angles we compute

${\hat {n}}\times \left({\hat {n}}\times {\vec {\beta }}\right)=\beta \left[-{\vec {\varepsilon }}_{\parallel }\sin \left({\frac {\beta ct}{\rho }}\right)+{\vec {\varepsilon }}_{\perp }\cos \left({\frac {\beta ct}{\rho }}\right)\sin \theta \right]$

$\omega \left(t-{\frac {{\hat {n}}\cdot {\vec {r}}(t)}{c}}\right)=\omega \left[t-{\frac {\rho }{c}}\sin \left({\frac {\beta ct}{\rho }}\right)\cos \theta \right]$

Substituting into the radiation integral and introducing

$\xi ={\frac {\rho \omega }{3c\gamma ^{3}}}\left(1+\gamma ^{2}\theta ^{2}\right)^{3/2}$

${\frac {d^{3}W}{d\Omega d\omega }}={\frac {e^{2}}{16\pi ^{3}\varepsilon _{0}c}}\left({\frac {2\omega \rho }{3c\gamma ^{2}}}\right)^{2}\left(1+\gamma ^{2}\theta ^{2}\right)^{2}\left[K_{2/3}^{2}(\xi )+{\frac {\gamma ^{2}\theta ^{2}}{1+\gamma ^{2}\theta ^{2}}}K_{1/3}^{2}(\xi )\right]\qquad (10),$

where the function K is a modified Bessel function of the second kind.

Frequency distribution of radiated energy

Angular distribution of radiated energy

From Eq.(10), we observe that the radiation intensity is negligible for $\xi \gg 1$. Critical frequency is defined as the frequency when ξ = 1/2 and θ = 0. So,

$\omega _{\text{c}}={\frac {3}{2}}{\frac {c}{\rho }}\gamma ^{3},$

and critical angle is defined as the angle for which $\xi (\theta _{\text{c}})\simeq \xi (0)+1$ and is approximately

$\theta _{\text{c}}\simeq {\frac {1}{\gamma }}\left({\frac {2\omega _{\text{c}}}{\omega }}\right)^{1/3}$

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.

${\frac {dW}{d\omega }}=\oint {\frac {d^{3}W}{d\omega d\Omega }}d\Omega ={\frac {{\sqrt {3}}e^{2}}{4\pi \varepsilon _{0}c}}\gamma {\frac {\omega }{\omega _{\text{c}}}}\int _{\omega /\omega _{\text{c}}}^{\infty }K_{5/3}(x)dx$

Frequency distribution of radiated energy

If we define

$S(y)\equiv {\frac {9{\sqrt {3}}}{8\pi }}y\int _{y}^{\infty }K_{5/3}(x)dx$

$\int _{0}^{\infty }S(y)dy=1,$

where y = ω/ω_c. Then

${\frac {dW}{d\omega }}={\frac {2e^{2}\gamma }{9\varepsilon _{0}c}}S(y).\qquad (11)$

Note that ${\frac {dW}{d\omega }}\sim {\frac {e^{2}}{4\pi \varepsilon _{0}c}}\left({\frac {\omega \rho }{c}}\right)^{1/3}$, if $\omega \ll \omega _{\text{c}}$, and ${\frac {dW}{d\omega }}\approx {\sqrt {\frac {3\pi }{2}}}{\frac {e^{2}}{4\pi \varepsilon _{0}c}}\gamma \left({\frac {\omega }{\omega _{\text{c}}}}\right)^{0.5}e^{-\omega /\omega _{\text{c}}}$, if $\omega \gg \omega _{\text{c}}$

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:

$\int _{\xi }^{\infty }K_{5/3}(x)dx={\frac {1}{\sqrt {3}}}\,\int _{0}^{\infty }\,{\frac {9+36x^{2}+16x^{4}}{(3+4x^{2}){\sqrt {1+x^{2}/3}}}}\exp \left[-\xi \left(1+{\frac {4x^{2}}{3}}\right){\sqrt {1+{\frac {x^{2}}{3}}}}\right]\ dx$

Synchrotron radiation emission as a function of the beam energy

Relationship between power radiated and the photon energy

First, define the critical photon energy as

$\varepsilon _{c}=\hbar \omega _{\text{c}}={\frac {3}{2}}{\frac {\hbar c}{\rho }}\gamma ^{3}.$

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.

Polarization of synchrotron radiation

In Eq.(10), the first term $K_{2/3}^{2}(\xi )$ is the radiation power with polarization in the orbit plane, and the second term ${\frac {\gamma ^{2}\theta ^{2}}{1+\gamma ^{2}\theta ^{2}}}K_{1/3}^{2}(\xi )$ is the polarization orthogonal to the orbit plane.

In the orbit plane $\theta =0$, the polarization is purely horizontal. Integrating on all frequencies, we get the angular distribution of the energy radiated

${\frac {d^{2}W}{d\Omega }}=\int _{0}^{\infty }{\frac {d^{3}W}{d\omega d\Omega }}d\omega ={\frac {7e^{2}\gamma ^{5}}{64\pi \varepsilon _{0}\rho }}{\frac {1}{(1+\gamma ^{2}\theta ^{2})^{5/2}}}\left[1+{\frac {5}{7}}{\frac {\gamma ^{2}\theta ^{2}}{1+\gamma ^{2}\theta ^{2}}}\right].\qquad (12)$

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.

Example 2: undulator

Solution of equation of motion and undulator equation

An undulator consists of a periodic array of magnets, so that they provide a sinusoidal magnetic field.

${\vec {B}}=\left(0,B_{0}\sin(k_{\text{u}}z),0\right)$

undulator

Solution of equation of motion is

${\vec {r}}(t)={\frac {\lambda _{\text{u}}K}{2\pi \gamma }}\sin \omega _{\text{u}}t\cdot {\hat {x}}+\left({\bar {\beta _{z}}}ct+{\frac {\lambda _{\text{u}}K^{2}}{16\pi \gamma ^{2}}}\cos(2\omega _{\text{u}}t)\right)\cdot {\hat {z}}$

where

$K={\frac {eB_{0}\lambda _{\text{u}}}{2\pi mc}},$

and

${\bar {\beta _{z}}}=1-{\frac {1}{2\gamma ^{2}}}\left(1+{\frac {K^{2}}{2}}\right),$

and the parameter $K$ is called the undulator parameter.

Constructive interference of the beam in the undulator

Condition for the constructive interference of radiation emitted at different poles is

$d={\frac {\lambda _{\text{u}}}{\bar {\beta }}}-\lambda _{\text{u}}\cos \theta =n\lambda$

Expanding $\cos \theta \approx 1-{\frac {\theta ^{2}}{2}}$ and neglecting the terms $O(\theta ^{2})$ in the resulting equation, one obtains

$\lambda _{n}={\frac {\lambda _{\text{u}}}{2\gamma ^{2}n}}\left({\frac {1+{\frac {K^{2}}{2}}+\gamma ^{2}\theta ^{2}}{\bar {\beta }}}\right)$

For ${\bar {\beta }}\rightarrow 1$, one finally gets

$\lambda _{n}={\frac {\lambda _{\text{u}}}{2\gamma ^{2}n}}\left(1+{\frac {K^{2}}{2}}+\gamma ^{2}\theta ^{2}\right)\qquad (13).$

This equation is called the undulator equation.

Radiation from the undulator

Radiation integral is

${\frac {d^{3}W}{d\Omega d\omega }}={\frac {e^{2}}{4\pi \varepsilon _{0}4\pi ^{2}c}}\left|\int _{-\infty }^{\infty }{\frac {{\hat {n}}\times \left[\left({\hat {n}}-{\vec {\beta }}\right)\times {\dot {\vec {\beta }}}\right]}{\left(1-{\hat {n}}\cdot {\vec {\beta }}\right)^{2}}}e^{i\omega (t-{\hat {n}}\cdot {\vec {r}}(t)/c)}dt\right|^{2}.$

Using the periodicity of the trajectory, we can split the radiation integral into a sum over $N_{u}$ terms.

${\frac {d^{3}W}{d\Omega d\omega }}={\frac {e^{2}\omega ^{2}}{4\pi \varepsilon _{0}4\pi ^{2}c}}\left|\int _{-\lambda _{u}/2{\bar {\beta }}c}^{\lambda _{u}/2{\bar {\beta }}c}{\hat {n}}\times \left({\hat {n}}\times {\vec {\beta }}\right)e^{i\omega (t-{\hat {n}}\cdot {\vec {r}}(t)/c)}dt\right|^{2}\left|1+e^{i\delta }+e^{2i\delta }+\cdots +e^{i(N_{u}-1)\delta }\right|^{2},\qquad (14)$

where 　${\bar {\beta }}=\beta \left(1-{\frac {K^{2}}{4\gamma ^{2}}}\right)$

Peak frequencies become sharp as the number N increases

, and $\delta ={\frac {2\pi \omega }{\omega _{\text{res}}(\theta )}}$,　$\omega _{\text{res}}(\theta )={\frac {2\pi c}{\lambda _{\text{res}}(\theta )}}$,　and　$\lambda _{\text{res}}(\theta )={\frac {\lambda _{u}}{2\gamma ^{2}}}\left(1+{\frac {K^{2}}{2}}+\gamma ^{2}\theta ^{2}\right).$

Only odd harmonics are radiated on-axis

Off-axis radiation contains many harmonics

The radiation integral in an undulator can be written as

${\frac {d^{3}W}{d\Omega d\omega }}={\frac {e^{2}\gamma ^{2}N^{2}}{4\pi \varepsilon _{0}c}}L\left(N{\frac {\Delta \omega _{n}}{\omega _{\text{res}}(\theta )}}\right)F_{n}(K,\theta ,\phi )\qquad (15).$

where $\Delta \omega _{n}=\omega -n\omega _{\text{res}}$ 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

$L\left(N{\frac {\Delta \omega _{n}}{\omega _{\text{res}}(\theta )}}\right)={\frac {\sin ^{2}\left(N\pi \Delta \omega _{n}/\omega _{\text{res}}(\theta )\right)}{N^{2}\left(\pi \Delta \omega _{n}/\omega _{\text{res}}(\theta )\right)^{2}}},$

and F_n depends on the angles of observations and K

$F_{n}(K,\theta ,\phi )\propto \left|\int _{-\lambda _{u}/2{\bar {\beta }}c}^{\lambda _{u}/2{\bar {\beta }}c}{\hat {n}}\times \left({\hat {n}}\times {\vec {\beta }}\right)e^{i\omega (t-{\hat {n}}\cdot {\vec {r}}(t)/c)}dt\right|^{2}.$

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

${\frac {d^{3}W}{d\Omega d\omega }}={\frac {e^{2}\gamma ^{2}N^{2}}{4\pi \varepsilon _{0}c}}L\left(N{\frac {\Delta \omega _{n}}{\omega _{\text{res}}(0)}}\right)F_{n}(K,0,0)$

and

$F_{n}(K,0,0)={\frac {n^{2}K^{2}}{1+K^{2}/2}}\left[J_{\frac {n+1}{2}}(Z)-J_{\frac {n-1}{2}}(Z)\right]^{2},$

where $Z={\frac {nK^{2}}{4(1+K^{2}/2)}}.$

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

See also

• Bremsstrahlung
• Cyclotron turnover
• Free-electron laser
• Radiation reaction
• Relativistic beaming
• Sokolov–Ternov effect

Notes

References

• 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. 

External links

• 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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• Chao J1, Li Z2, Li J3, Peng H2, Su S1, Li Q2, Zhu C3, Zuo X2, Song S2, Wang L1, Wang L4.
• Biosensors & bioelectronics.Biosens Bioelectron.2016 Jul 15;81:92-6. doi: 10.1016/j.bios.2016.01.093. Epub 2016 Feb 19.
• Microarrays of biomolecules hold great promise in the fields of genomics, proteomics, and clinical assays on account of their remarkably parallel and high-throughput assay capability. However, the fluorescence detection used in most conventional DNA microarrays is still limited by sensitivity. In th
• PMID 26922047

• Identification of the dominant photochemical pathways and mechanistic insights to the ultrafast ligand exchange of Fe(CO)5 to Fe(CO)4EtOH.

• Kunnus K, Josefsson I1, Rajkovic I2, Schreck S, Quevedo W3, Beye M3, Weniger C3, Grübel S2, Scholz M2, Nordlund D4, Zhang W5, Hartsock RW5, Gaffney KJ5, Schlotter WF6, Turner JJ6, Kennedy B3, Hennies F7, de Groot FM8, Techert S, Odelius M1, Wernet P3, Föhlisch A.
• Structural dynamics (Melville, N.Y.).Struct Dyn.2016 Feb 9;3(4):043204. doi: 10.1063/1.4941602. eCollection 2016.
• We utilized femtosecond time-resolved resonant inelastic X-ray scattering and ab initio theory to study the transient electronic structure and the photoinduced molecular dynamics of a model metal carbonyl photocatalyst Fe(CO)5 in ethanol solution. We propose mechanistic explanation for the parallel
• PMID 26958587

Japanese Journal

• 放射光蛍光X線分析を用いるモエジマシダ(Ptris vittata L.)におけるクロム蓄積機構の解明 (年間特集 生)

• 分析化学 64(11), 801-810, 2015-11
• NAID 40020654384

• 分析化学における放射光の利用 放射光分析の応用 : 環境分析

• ぶんせき 2015(11), 478-485, 2015-11
• NAID 40020654207

• Direct Evidence of the Symmetry Change of Co-3<italic>d</italic>Orbitals Associated with the Spin-State Transition in LaCoO₃by X-ray Compton Scattering

• Journal of the Physical Society of Japan 84(11), 2015-10-19
• NAID 160000000891

Related Links

• Synchrotron Radiation Centerとは - goo Wikipedia (ウィキペディア)

The Synchrotron Radiation Center (SRC), located in Stoughton, Wisconsin and operated by the University of Wisconsin–Madison, is a national synchrotron light source research facility, operating the Aladdin storage ring. From 1968 ...

• Synchrotron Radiation - Astrophysics Research Projects

Synchrotron Radiation The synchrotron radiation, the emission of very relativistic and ultrarelativistic electrons gyrating in a magnetic field, is the process which dominates much of high energy astrophysics. It was originally observed ...

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★リンクテーブル★

リンク元	「シンクロトロン放射光」
関連記事	「radiation」「synchrotron」

「シンクロトロン放射光」

　　[★]

英

synchrotron radiation

関

シンクロトロン

「radiation」

　　[★]

• n.

• 放射、放射線
• 放射物
• 輻射、放熱

　 　 　 　 　 　

「synchrotron」

　　[★]

• シンクロトロン