Editing Cyclotron radiation

{{short description|Radiation emitted by charged particles deflected by magnetic field}}

In [[particle physics]], '''cyclotron radiation''' is [[electromagnetic radiation]] emitted by non-relativistic accelerating [[electric charge|charge]]d particles deflected by a [[magnetic field]].<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>  The [[Lorentz force]] on the particles acts perpendicular to both the magnetic [[field line]]s and the particles' motion through them, creating an acceleration of charged particles that causes them to emit radiation as a result of the acceleration they undergo as they spiral around the lines of the magnetic field.

The name of this radiation derives from the [[cyclotron]], a type of [[particle accelerator]] used since the 1930s to create highly energetic particles for study. The cyclotron makes use of the circular orbits that charged particles exhibit in a uniform magnetic field. Furthermore, the period of the orbit is independent of the energy of the particles, allowing the cyclotron to operate at a set [[frequency]]. Cyclotron radiation is emitted by all charged particles travelling through magnetic fields, not just those in cyclotrons. Cyclotron radiation from [[Plasma (physics)|plasma]] in the [[interstellar medium]] or around [[black hole]]s and other astronomical phenomena is an important source of information about distant magnetic fields.<ref>{{cite journal|last1=Dogiel|first1=V. A.|title=Gamma-ray astronomy|journal=Contemporary Physics|date=March 1992|volume=33|issue=2|pages=91–109|doi=10.1080/00107519208219534|bibcode=1992ConPh..33...91D}}</ref><ref>{{cite journal|last1=Zheleznyakov|first1=V. V.|title=Space plasma under extreme conditions|journal=Radiophysics and Quantum Electronics|date=January 1997|volume=40|issue=1–2|pages=3–15|doi=10.1007/BF02677820|bibcode=1997R&QE...40....3Z|s2cid=121796067}}</ref>

==Properties==
The [[Power (physics)|power]] (energy per unit time) of the emission of each electron can be calculated:<ref>{{cite book|last1=Longair|first1=Malcolm S.|title=High Energy Astrophysics: Volume 2, Stars, the Galaxy and the Interstellar Medium|date=1994|publisher=[[Cambridge University Press]]|isbn=9780521435840|page=232|url=https://books.google.com/books?id=x1TMSMpzD2UC&pg=PA232|language=en}}</ref>

: <math>{-dE \over dt}={\sigma_t B^2 v^2 \over c \mu_0} </math>

where ''E'' is energy, ''t'' is time, <math> \sigma_t </math> is the [[Thomson cross section]] (total, not differential), ''B'' is the magnetic field strength, ''v'' is the velocity perpendicular to the magnetic field, ''c'' is the speed of light and <math> \mu_0 </math> is the [[permeability of free space]].{{verify source|date=December 2023}}

Cyclotron radiation has a spectrum with its main spike at the same fundamental frequency as the particle's orbit, and [[harmonic]]s at higher integral factors. Harmonics are the result of imperfections in the actual emission environment, which also create a broadening of the [[spectral line]]s.<ref>{{cite book|last1=Hilditch|first1=R. W.|title=An Introduction to Close Binary Stars|date=2001|publisher=Cambridge University Press|isbn=9780521798006|page=327|url=https://books.google.com/books?id=hJSADIxyheoC&pg=PA327|language=en}}</ref> The most obvious source of line broadening is non-uniformities in the magnetic field;<ref>{{cite book|last1=Cairns|first1=R. A.|title=Plasma Physics|date=2012|publisher=Springer|isbn=9789401096553|page=SA7–PA8|url=https://books.google.com/books?id=-3agBwAAQBAJ&pg=SA7-PA8|language=en}}</ref> as an electron passes from one area of the field to another, its emission frequency will change with the strength of the field. Other sources of broadening include collisional broadening<ref>{{cite conference |url=http://www-naweb.iaea.org/napc/physics/2ndgenconf/data/Proceedings%201958/papers%20Vol32/Paper47_Vol32.pdf |title=Cyclotron Radiation from a Magnetized Plasma |last1=Hayakawa |first1=S |last2=Hokkyō|first2=N |last3=Terashima |first3=Y |last4=Tsuneto |first4=T. |date=1958 |conference=2nd Geneva Conference on Peaceful Uses of Atomic Energy }}</ref> as the electron will invariably fail to follow a perfect orbit, distortions of the emission caused by interactions with the surrounding plasma, and [[special relativity|relativistic]] effects if the charged particles are sufficiently energetic.  When the electrons are moving at relativistic speeds, cyclotron radiation is known as [[synchrotron radiation]].

The recoil experienced by a particle emitting cyclotron radiation is called [[radiation reaction]]. Radiation reaction acts as a resistance to motion in a cyclotron; and the work necessary to overcome it is the main energetic cost of accelerating a particle in a cyclotron. Cyclotrons are prime examples of systems which experience radiation reaction.

==Examples==

In the context of [[magnetic fusion energy]], cyclotron radiation losses translate into a [[Aneutronic fusion#Power balance|requirement]] for a minimum plasma energy density in relation to the magnetic field energy density.

Cyclotron radiation would likely be produced in a [[high altitude nuclear explosion]]. [[Gamma ray]]s produced by the explosion would [[ionization|ionize]] [[atom]]s in the upper atmosphere and those free electrons would interact with the Earth's magnetic field to produce cyclotron radiation in the form of an [[electromagnetic pulse]] (EMP).  This phenomenon is of concern to the military as the EMP may damage [[Solid-state electronics|solid state]] electronic equipment.

==See also==
*[[Auroral kilometric radiation]] (AKR)
*[[Bremsstrahlung]]
*[[Beamstrahlung]]
*[[Synchrotron radiation]]
*[[Free electron laser]]
*[[Larmor formula]]

==References==
{{Reflist}}

{{DEFAULTSORT:Cyclotron Radiation}}
[[Category:Electromagnetic radiation]]
[[Category:Plasma phenomena]]
[[Category:Experimental particle physics]]