Editing Synchrotron (section)

== Principle of operation ==
The synchrotron evolved from the [[cyclotron]], the first cyclic particle accelerator. While a classical [[cyclotron]] uses both a constant guiding [[magnetic field]] and a constant-frequency [[electromagnetic field]] (and is working in [[classical mechanics|classical approximation]]), its successor, the [[isochronous cyclotron]], works by local variations of the guiding magnetic field, adapting to the increasing [[relativistic mass]] of particles during acceleration.<ref>{{Cite journal |last=McMillan |first=Edwin M. |date=February 1984 |title=A history of the synchrotron |url=http://physicstoday.scitation.org/doi/10.1063/1.2916080 |journal=Physics Today |language=en |volume=37 |issue=2 |pages=31–37 |doi=10.1063/1.2916080 |s2cid=121370125 |issn=0031-9228|url-access=subscription }}</ref>

[[File:Cosmotron (PSF).png|thumb|A drawing of the Cosmotron]]
In a synchrotron, this adaptation is done by variation of the magnetic field strength in time, rather than in space. For particles that are not close to the speed of [[light]], the frequency of the applied electromagnetic field may also change to follow their non-constant circulation time. By increasing these [[parameter]]s accordingly as the particles gain energy, their circulation path can be held constant as they are accelerated. This allows the vacuum chamber for the particles to be a large thin [[torus]], rather than a disk as in previous, compact accelerator designs. Also, the thin profile of the vacuum chamber allowed for a more efficient use of magnetic fields than in a cyclotron, enabling the cost-effective construction of larger synchrotrons.{{Citation needed|date=January 2021}}

While the first synchrotrons and storage rings like the [[Cosmotron]] and [[Anello Di Accumulazione|ADA]] strictly used the toroid shape, the [[strong focusing]] principle independently discovered by [[Ernest Courant]] et al.<ref>{{Cite journal | last1 = Courant | first1 = E. D. | author-link1 = Ernest Courant| last2 = Livingston | first2 = M. S. | author-link2 = Milton Stanley Livingston| last3 = Snyder | first3 = H. S. | author-link3 = Hartland Sweet Snyder| doi = 10.1103/PhysRev.88.1190 | bibcode = 1952PhRv...88.1190C| title = The Strong-Focusing Synchrotron—A New High Energy Accelerator | journal = [[Physical Review]] | volume = 88 | issue = 5 | pages = 1190–1196| year = 1952 | hdl = 2027/mdp.39015086454124 | hdl-access = free }}</ref><ref>{{Cite journal | last1 = Blewett | first1 = J. P.| title = Radial Focusing in the Linear Accelerator | doi = 10.1103/PhysRev.88.1197 | bibcode = 1952PhRv...88.1197B| journal = [[Physical Review]] | volume = 88 | issue = 5 | pages = 1197–1199| year = 1952 }}</ref> and [[Nicholas Christofilos]]<ref>{{US patent reference | number = 2736799 | y = 1956 | m = 02 | d = 28 | inventor = [[Nicholas Christofilos]] | title = [https://patents.google.com/patent/US2736799 Focussing System for Ions and Electrons] }}</ref> allowed the complete separation of the accelerator into components with specialized functions along the particle path, shaping the path into a round-cornered polygon. Some important components are given by [[RF cavity|radio frequency cavities]] for direct acceleration, [[dipole magnet]]s (''bending magnets'') for deflection of particles (to close the path), and [[quadrupole magnet|quadrupole]] / [[sextupole magnet]]s for beam focusing.<ref>{{Cite book |last1=Muto |first1=M. |last2=Niki |first2=K. |last3=Mori |first3=Y. |chapter=Magnets and their power supplies of JHF 50-GeV synchrotron |date=May 1997 |title=Proceedings of the 1997 Particle Accelerator Conference (Cat. No.97CH36167) |chapter-url=https://ieeexplore.ieee.org/document/753190 |volume=3 |pages=3306–3308 vol.3 |doi=10.1109/PAC.1997.753190|isbn=0-7803-4376-X }}</ref>

[[File:Aust.-Synchrotron-Interior-Panorama,-14.06.2007.jpg|thumb|right|320px|The interior of the [[Australian Synchrotron]] facility, a [[synchrotron light source]]. Dominating the image is the [[storage ring]], showing a [[Beamline#Synchrotron radiation beamline|beamline]] at front right. The storage ring's interior includes a synchrotron and a [[Linear accelerator|linac]].]]
The combination of time-dependent guiding magnetic fields and the strong focusing principle enabled the design and operation of modern large-scale accelerator facilities like [[collider]]s and [[synchrotron light source]]s. The straight sections along the closed path in such facilities are not only required for radio frequency cavities, but also for [[particle detector]]s (in colliders) and photon generation devices such as [[Wiggler (synchrotron)|wigglers]] and [[undulator]]s (in third generation synchrotron light sources).{{Citation needed|date=January 2021}}

The maximum energy that a cyclic accelerator can impart is typically limited by the maximum strength of the magnetic fields and the minimum radius (maximum [[curvature]]) of the particle path. Thus one method for increasing the energy limit is to use [[superconducting magnet]]s, these not being limited by [[magnetic saturation]]. [[Electron]]/[[positron]] accelerators may also be limited by the emission of [[synchrotron radiation]], resulting in a partial loss of the particle beam's kinetic energy. The limiting beam energy is reached when the energy lost to the lateral acceleration required to maintain the beam path in a circle equals the energy added each cycle.{{Citation needed|date=January 2021}}

More powerful accelerators are built by using large radius paths and by using more numerous and more powerful microwave cavities. Lighter particles (such as electrons) lose a larger fraction of their energy when deflected. Practically speaking, the energy of [[electron]]/[[positron]] accelerators is limited by this radiation loss, while this does not play a significant role in the dynamics of [[proton]] or [[ion]] accelerators. The energy of such accelerators is limited strictly by the strength of magnets and by the cost.{{Citation needed|date=January 2021}}

=== Injection procedure ===
Unlike in a cyclotron, synchrotrons are unable to accelerate particles from zero kinetic energy; one of the obvious reasons for this is that its closed particle path would be cut by a device that emits particles. Thus, schemes were developed to inject pre-accelerated [[particle beam]]s into a synchrotron. The pre-acceleration can be realized by a chain of other accelerator structures like a [[linac]], a [[microtron]] or another synchrotron; all of these in turn need to be fed by a particle source comprising a simple high voltage power supply, typically a [[Cockcroft-Walton generator]].{{Citation needed|date=January 2021}}

Starting from an appropriate initial value determined by the injection energy, the field strength of the [[dipole magnet]]s is then increased. If the high energy particles are emitted at the end of the acceleration procedure, e.g. to a target or to another accelerator, the field strength is again decreased to injection level, starting a new ''injection cycle''. Depending on the method of magnet control used, the time interval for one cycle can vary substantially between different installations.{{Citation needed|date=January 2021}}