View source for Physics:Synchrotron radiation

{{Short description|Electromagnetic radiation emitted by charged particles accelerated  perpendicular to their velocity}}

'''Synchrotron radiation''' (also known as '''magnetobremsstrahlung radiation''') is the [[Physics:Electromagnetic radiation|electromagnetic radiation]] emitted when [[Physics:Theory of relativity|relativistically]] charged particles are subject to an acceleration perpendicular to their velocity ({{math|'''a''' &perp; '''v'''}}). It is produced artificially in some types of [[Physics:Particle accelerator|particle accelerator]]s or naturally by fast electrons moving through magnetic fields. The radiation produced in this way has a characteristic [[Physics:Polarization (waves)|polarization]], and the frequencies generated can range over a large portion of the [[Physics:Electromagnetic spectrum|electromagnetic spectrum]].<ref>{{Cite journal |date=2010-03-02 |title=What is synchrotron radiation? |url=https://www.nist.gov/pml/sensor-science/what-synchrotron-radiation |journal=NIST |language=en}}</ref>
[[File:Radiacao escalar SdS.pdf|thumb|Pictorial representation of the radiation emission process by a source moving around a [[Astronomy:Schwarzschild metric|Schwarzschild black hole]] in a de Sitter universe. ]]

Synchrotron radiation is similar to [[Physics:Bremsstrahlung|bremsstrahlung radiation]], which is emitted by a charged particle when the acceleration is parallel to the direction of motion. The general term for radiation emitted by particles in a magnetic field is ''gyromagnetic radiation'', for which synchrotron radiation is the ultra-relativistic special case. Radiation emitted by charged particles moving non-relativistically in a magnetic field is called [[Physics:Cyclotron radiation|cyclotron emission]].<ref>{{cite journal|last1=Monreal|first1=Benjamin|title=Single-electron cyclotron radiation|journal=Physics Today|date=Jan 2016|volume=69|issue=1|page=70|doi=10.1063/pt.3.3060|bibcode=2016PhT....69a..70M|doi-access=free}}</ref> For particles in the mildly relativistic range (≈85% of the speed of light), the emission is termed ''gyro-synchrotron radiation''.<ref>{{cite web |last1=Chen |first1=Bin |title=Radiative processes from energetic particles II: Gyromagnetic radiation |url=https://web.njit.edu/~binchen/phys780/LectureNotes/lec21.pdf |website=New Jersey Institute of Technology |access-date=10 December 2021}}</ref>

In [[Physics:Astrophysics|astrophysics]], synchrotron emission occurs, for instance, due to ultra-relativistic motion of a charged particle around a [[Astronomy:Black hole|black hole]].<ref>{{Cite journal|last1=Brito|first1=João P. B.|last2=Bernar|first2=Rafael P.|last3=Crispino|first3=Luís C. B.|date=11 June 2020|title=Synchrotron geodesic radiation in Schwarzschild–de Sitter spacetime|journal=Physical Review D|language=en|volume=101|issue=12|pages=124019|doi=10.1103/PhysRevD.101.124019|issn=2470-0010|arxiv=2006.08887|bibcode=2020PhRvD.101l4019B|s2cid=219708236}}</ref> When the source follows a circular [[Geodesics in general relativity|geodesic]] around the black hole, the synchrotron radiation occurs for orbits close to the [[Astronomy:Photon sphere|photosphere]] where the motion is in the [[Ultrarelativistic limit|ultra-relativistic]] regime. 
[[File:Syncrotron.png|thumb|Synchrotron radiation from a bending magnet]] [[File:Undulator (numbers).svg|thumb|Synchrotron radiation from an undulator]]
[[File:Emmaalexander synchrotron.png|thumb|Synchrotron radiation from an astronomical source]]

==History==

Synchrotron radiation was first observed by technician Floyd Haber, on April 24, 1947, at the 70 MeV electron synchrotron of the [[Company:General Electric|General Electric]] research laboratory in Schenectady, New York.<ref>{{cite journal |last1=Elder |first1=F. R. |last2=Gurewitsch |first2=A. M. |last3=Langmuir |first3=R. V. |last4=Pollock |first4=H. C. |title=Radiation from Electrons in a Synchrotron |journal= [[Physics:Physical Review|Physical Review]] |publisher= [[Organization:American Physical Society|American Physical Society]] |volume=71 |issue=11 |date=1 June 1947 |issn=0031-899X |doi= 10.1103/physrev.71.829.5 |pages=829–830|bibcode=1947PhRv...71..829E }}</ref> While this was not the first [[Physics:Synchrotron|synchrotron]] built, it was the first with a transparent [[Physics:Vacuum tube|vacuum tube]], allowing the radiation to be directly observed.<ref>{{cite journal |last1=Mitchell |first1=Edward |last2=Kuhn |first2=Peter |last3=Garman |first3=Elspeth |title=Demystifying the synchrotron trip: a first time user's guide |journal=Structure |date=May 1999 |volume=7 |issue=5 |pages=R111–R121 |doi=10.1016/s0969-2126(99)80063-x |pmid=10378266 |doi-access=free }}</ref>

As recounted by Herbert Pollock:<ref>{{cite journal |last1=Pollock |first1=Herbert C. |title=The discovery of synchrotron radiation |journal=American Journal of Physics |date=March 1983 |volume=51 |issue=3 |pages=278–280 |doi=10.1119/1.13289 |bibcode=1983AmJPh..51..278P |doi-access=free }}</ref>

{{blockquote|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 [[Physics:Cherenkov radiation|Cherenkov radiation]], but it soon became clearer that we were seeing [[Biography:Dmitri Ivanenko|Ivanenko]] and [[Biography:Isaak Pomeranchuk|Pomeranchuk]] radiation.<ref>{{cite journal |last1=Iwanenko |first1=D. |last2= Pomeranchuk |first2=I. |title=On the Maximal Energy Attainable in a Betatron |journal= Physical Review |publisher= American Physical Society |volume=65 |issue=11–12 |date=1 June 1944 |issn=0031-899X |doi= 10.1103/physrev.65.343 |page=343|bibcode=1944PhRv...65..343I }}</ref>}}

==Description==
A direct consequence of [[Physics:Maxwell's equations|Maxwell's equations]] is that accelerated charged particles always emit electromagnetic radiation. Synchrotron radiation is the special case of charged particles moving at relativistic speed undergoing acceleration perpendicular to their direction of motion, typically in a magnetic field. In such a field, the force due to the field is always perpendicular to both the direction of motion and to the direction of field, as shown by the [[Physics:Lorentz force|Lorentz force law]].

The power carried by the radiation is found (in SI units) by the [[Physics:Larmor formula#Relativistic generalization|relativistic Larmor formula]]:<ref>{{cite book |last1=Wilson |first1=E. J. N. |title=An introduction to particle accelerators |date=2001 |publisher=Oxford University Press |location=Oxford |isbn=0-19-850829-8 |pages=221–223}}</ref><ref>{{cite book|first1=Richard|language=en|last1=Fitzpatrick |page=299|title=Classical Electromagnetism|url=https://farside.ph.utexas.edu/teaching/jk1/Electromagnetism.pdf}}<!-- auto-translated by Module:CS1 translator --></ref>

<math display="block">P_\gamma = \frac{q^2}{6 \pi \varepsilon_0 c^3} a^2 \gamma^4 = \frac{q^2 c}{6 \pi \varepsilon_0} \frac{\beta^4 \gamma^4}{\rho^2} ,</math>
where
* <math>\varepsilon_0</math> is the [[Physics:Vacuum permittivity|vacuum permittivity]],
* <math>q</math> is the particle charge,
* <math>a</math> is the magnitude of the acceleration,
* <math>c</math> is the speed of light,
* <math>\gamma</math> is the [[Lorentz factor]],
* <math>\beta = v/c</math>,
* <math>\rho</math> is the [[Physics:Radius of curvature|radius of curvature]] of the particle trajectory.

The force on the emitting electron is given by the Abraham–Lorentz–Dirac force.

When the radiation is emitted by a particle moving in a plane, the radiation is linearly polarized when observed in that plane, and circularly polarized when observed at a small angle. Considering quantum mechanics, however, this radiation is emitted in discrete packets of photons and has significant effects in accelerators called [[Physics:Quantum excitation (accelerator physics)|quantum excitation]]. For a given acceleration, the average energy of emitted photons is proportional to <math>\gamma^3</math> and the emission rate to <math>\gamma</math>.

==From accelerators==
{{main|Engineering:Synchrotron light source}}

Circular accelerators will always produce gyromagnetic radiation as the particles are deflected in the magnetic field.  However, the quantity and properties of the radiation are highly dependent on the nature of the acceleration taking place.  For example, due to the difference in mass, the factor of <math>\gamma^4</math> in the formula for the emitted power means that electrons radiate energy at approximately 10<sup>13</sup> times the rate of protons.<ref>{{cite book |last1=Conte |first1=Mario |last2=MacKay |first2=William |title=An introduction to the physics of particle accelerators |date=2008 |publisher=World Scientific |location=Hackensack, N.J. |isbn=978-981-277-960-1 |page=166 |edition=2nd}}</ref>

Energy loss from synchrotron radiation in circular accelerators was originally considered a nuisance, as additional energy must be supplied to the beam in order to offset the losses.  However, beginning in the 1980s, circular electron accelerators known as [[Engineering:Synchrotron light source|light sources]] have been constructed to deliberately produce intense beams of synchrotron radiation for research.<ref>{{cite web |title=History: Of X-rays and synchrotrons |url=https://lightsources.org/history/ |website=lightsources.org |date=21 September 2017 |access-date=13 December 2021}}</ref>

==In astronomy==
[[Image:M87 jet.jpg|thumb|225px|Messier 87's astrophysical jet, HST image. The blue light from the jet emerging from the bright [[Active galactic nucleus|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 power-law energy spectra and polarization.<ref>Vladimir A. Bordovitsyn, "[https://books.google.com/books?id=rG9ZWoCtwagC&dq=%22Synchrotron++radiation%22+astronomy&pg=PA385 Synchrotron Radiation in Astrophysics]" (1999) ''[http://www.worldscibooks.com/physics/3492.html Synchrotron Radiation Theory and Its Development]'', {{ISBN|981-02-3156-3}}</ref> It is considered to be one of the most powerful tools in the study of extra-solar magnetic fields wherever relativistic charged particles are present. Most known cosmic radio sources emit synchrotron radiation. It is often used to estimate the strength of large cosmic magnetic fields as well as analyze the contents of the interstellar and intergalactic media.<ref name="Klein 2014">{{cite book|last=Klein|first=Ulrich|title=Galactic and intergalactic magnetic fields|publisher=Springer|location=Cham, Switzerland & New York|year=2014|isbn=978-3-319-08942-3|oclc=894893367}}</ref>

===History of detection===
This type of radiation was first detected in a jet emitted by [[Astronomy:Messier 87|Messier 87]] in 1956 by Geoffrey R. Burbidge,<ref>{{cite journal|last=Burbidge|first=G. R.|title=On Synchrotron Radiation from Messier 87|journal=The Astrophysical Journal|publisher=IOP Publishing|volume=124|year=1956|issn=0004-637X|doi=10.1086/146237|page=416|bibcode=1956ApJ...124..416B|doi-access=free}}</ref> who saw it as confirmation of a prediction by Iosif S. Shklovsky in 1953. However, it had been predicted earlier (1950) by [[Biography:Hannes Alfvén|Hannes Alfvén]] and Nicolai Herlofson.<ref>{{cite journal|last1=Alfvén|first1=H.|last2=Herlofson|first2=N.|title=Cosmic Radiation and Radio Stars|journal=Physical Review|publisher=APS|volume=78|issue=5|date=1 June 1950|issn=0031-899X|doi=10.1103/physrev.78.616|page=616|bibcode=1950PhRv...78..616A}}</ref> Solar flares accelerate particles that emit in this way, as suggested by R. Giovanelli in 1948 and described by J.H. Piddington in 1952.<ref>{{cite journal|last=Piddington|first=J. H.|title=Thermal Theories of the High-Intensity Components of Solar Radio-Frequency Radiation|journal=Proceedings of the Physical Society. Section B|publisher=IOP Publishing|volume=66|issue=2|year=1953|issn=0370-1301|doi=10.1088/0370-1301/66/2/305|pages=97–104|bibcode=1953PPSB...66...97P}}</ref>

T. K. Breus noted that questions of priority on the history of astrophysical synchrotron radiation are complicated, writing:

[[Image:Crab Nebula.jpg|225px|thumb|'''[[Astronomy:Crab Nebula|Crab Nebula]].''' The bluish glow from the central region of the nebula is due to synchrotron radiation.]]

=== From supermassive black holes ===

It has been suggested that [[Astronomy:Supermassive black hole|supermassive black hole]]s produce synchrotron radiation in "jets", generated by the gravitational acceleration of ions in their polar magnetic fields. The nearest such observed jet is from the core of the galaxy [[Astronomy:Messier 87|Messier 87]].  This jet is interesting for producing the illusion of superluminal motion as observed from the frame of Earth. 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, giving the illusion of faster than light travel, despite the fact that there is actually no violation of [[Physics:Special relativity|special relativity]].<ref>{{cite web|last=Chase|first=Scott I.|title=Apparent Superluminal Velocity of Galaxies|url=http://math.ucr.edu/home/baez/physics/Relativity/SpeedOfLight/Superluminal/superluminal.html|access-date=22 August 2012}}</ref>

===Pulsar wind nebulae===
A class of [[Astronomy:Astronomical object|astronomical source]]s where synchrotron emission is important is [[Astronomy:Pulsar wind nebula|pulsar wind nebula]]e, also known as plerions, of which the Crab nebula and its associated [[Astronomy:Pulsar|pulsar]] are archetypal.
Pulsed emission gamma-ray radiation from the Crab has recently been observed up to ≥25&nbsp;GeV,<ref>{{cite journal|last1=Aliu|first1=E.|last2=Anderhub|first2=H.|last3=Antonelli|first3=L. A.|last4=Antoranz|first4=P.|last5=Backes|first5=M.|last6=Baixeras|first6=C.|last7=Barrio|first7=J. A.|last8=Bartko|first8=H.|last9=Bastieri|first9=D.|last10=Becker|first10=J. K.|display-authors=5|title=Observation of Pulsed γ-Rays Above 25 GeV from the Crab Pulsar with MAGIC|journal=Science|volume=322|issue=5905|date=21 November 2008|issn=0036-8075|doi=10.1126/science.1164718|pages=1221–1224|pmid=18927358|arxiv=0809.2998|bibcode=2008Sci...322.1221A|s2cid=5387958 }}</ref> probably due to synchrotron emission by electrons trapped in the strong magnetic field around the pulsar.
Polarization in the Crab nebula<ref>{{cite journal|last1=Dean|first1=A. J.|last2=Clark|first2=D. J.|last3=Stephen|first3=J. B.|last4=McBride|first4=V. A.|last5=Bassani|first5=L.|last6=Bazzano|first6=A.|last7=Bird|first7=A. J.|last8=Hill|first8=A. B.|last9=Shaw|first9=S. E.|last10=Ubertini|first10=P.|display-authors=5|title=Polarized Gamma-Ray Emission from the Crab|journal=Science|publisher=American Association for the Advancement of Science (AAAS)|volume=321|issue=5893|date=29 August 2008|issn=0036-8075|doi=10.1126/science.1149056|pages=1183–1185|pmid=18755970 |bibcode=2008Sci...321.1183D|s2cid=206509342}}</ref> at energies from 0.1 to 1.0 MeV, illustrates this typical property of synchrotron radiation.

===Interstellar and intergalactic media===
Much of what is known about the magnetic environment of the [[Astronomy:Interstellar medium|interstellar medium]] and intergalactic medium is derived from observations of synchrotron radiation. Cosmic ray electrons moving through the medium interact with relativistic plasma and emit synchrotron radiation which is detected on Earth. The properties of the radiation allow astronomers to make inferences about the magnetic field strength and orientation in these regions. However, accurate calculations of field strength cannot be made without knowing the relativistic electron density.<ref name="Klein 2014"/>

===In supernovae===
When a star explodes in a supernova, the fastest ejecta move at semi-relativistic speeds approximately 10% the [[Physics:Speed of light|speed of light]].<ref>{{cite journal |last1=Soderberg |first1=A. |last2=Chevalier |first2=R. A. |last3=Kulkarni |first3=S. R. |last4=Frail |first4=D. A. |date=November 2006 |title=The Radio and X-Ray Luminous SN 2003bg and the Circumstellar Density Variations around Radio Supernovae |journal=The Astrophysical Journal |volume=651 |issue=2 |pages=1005–1018 |doi=10.1086/507571|doi-access=free |arxiv=astro-ph/0512413 }}</ref> This blast wave gyrates electrons in ambient magnetic fields and generates synchrotron emission, revealing the radius of the blast wave at the location of the emission.<ref>{{cite journal |last1=Chevalier |first1=R. A. |date=May 1998 |title=Synchrotron Self-Absorption in Radio Supernovae |journal=The Astrophysical Journal |volume=499 |issue=2 |pages=810–819 |doi=10.1086/305676|doi-access=free }}</ref> Synchrotron emission can also reveal the strength of the magnetic field at the front of the shock wave, as well as the circumstellar density it encounters, but strongly depends on the choice of energy partition between the magnetic field, proton kinetic energy, and electron kinetic energy. Radio synchrotron emission has allowed astronomers to shed light on mass loss and stellar winds that occur just prior to stellar death.<ref>{{cite journal |last1=Margutti |first1=Raffaella |last2=Kamble |first2=A. |last3=Milisavljevic |first3=D. |last4=Zapartas |first4=E. |last5=de Mink |first5=S. E. |last6=Drout |first6=M. |last7=Chornock |first7=R. |display-authors=1 |date=February 2017 |title=Ejection of the Massive Hydrogen-rich Envelope Timed with the Collapse of the Stripped SN 2014C |journal=The Astrophysical Journal |volume=835 |issue=2 |page=140 |doi=10.3847/1538-4357/835/2/140|hdl=10150/624387 |hdl-access=free |doi-access=free }}</ref><ref>{{cite journal |last1=DeMarchi |first1=Lindsay |last2=Margutti |first2=R. |last3=Dittman |first3=J. |last4=Brunthaler |first4=A. |display-authors=1 |date=October 2022 |title=Radio Analysis of SN2004C Reveals an Unusual CSM Density Profile as a Harbinger of Core Collapse |journal=The Astrophysical Journal |volume=938 |issue=1 |page=84 |doi=10.3847/1538-4357/ac8c26|doi-access=free |arxiv=2203.07388 }}</ref>

==See also==
* {{annotated link|Physics:Bremsstrahlung}}
* {{annotated link|Physics:Cyclotron turnover}}
* {{annotated link|Physics:Cyclotron radiation}}
* {{annotated link|Physics:Free-electron laser}}
* {{annotated link|Astronomy:Relativistic beaming}}
* {{annotated link|Physics:Sokolov–Ternov effect}}
* {{annotated link|Synchrotron function}}

==Notes==
{{Reflist|30em}}

==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}}
* {{cite web|last=[[Biography:Ishfaq Ahmad|Ishfaq Ahmad]], D.Sc.|title=Measurements of the Relative Oscillator Strengths using the Synchrotron Radiation|url=http://pps-pak.org/proceedings/Eleventh-Proc-2009.pdf|work=Proceedings of the National Syposium on Frontier of Physics, National Centre for Theoretical Physics|publisher=Pakistan Physical Society|access-date=16 January 2012}}

==External links==
* [http://cdsads.u-strasbg.fr/cgi-bin/nph-bib_query?bibcode=1965ARA%26A...3..297G Cosmic Magnetobremsstrahlung (synchrotron Radiation)], by Ginzburg, V. L., Syrovatskii, S. I., ARAA, 1965
* [http://cdsads.u-strasbg.fr/cgi-bin/nph-bib_query?bibcode=1969ARA%26A...7..375G Developments in the Theory of Synchrotron Radiation and its Reabsorption], by Ginzburg, V. L., Syrovatskii, S. I., ARAA, 1969
* [http://www.lightsources.org Lightsources.org]
* [http://biosync.sbkb.org BioSync] – a structural biologist's resource for high energy data collection facilities
* [http://xdb.lbl.gov X-Ray Data Booklet]

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{{Sourceattribution|Synchrotron radiation}}