Editing Synchrotron light source (section)

==Synchrotron radiation from accelerators==
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 gigaelectronvolt range. The electrons are forced to travel in a closed path by strong magnetic fields. This is similar to a radio antenna, but with the difference that the relativistic speed changes the observed frequency due to the Doppler effect by a factor <math>\gamma</math>. Relativistic [[Lorentz contraction]] bumps the frequency by another factor of <math>\gamma</math>, thus multiplying the gigahertz frequency of the resonant cavity that accelerates the electrons into the X-ray range. Another dramatic effect of [[special relativity|relativity]] is that the radiation pattern is distorted from the isotropic dipole pattern expected from non-relativistic theory into an extremely forward-pointing cone of radiation. This makes synchrotron radiation sources the most brilliant known sources of X-rays. The planar acceleration geometry makes the radiation linearly polarized when observed in the orbital plane, and circularly polarized when observed at a small angle to that plane.{{Citation needed|date=January 2021}}

The advantages of using synchrotron radiation for spectroscopy and diffraction have been realized by an ever-growing scientific community, beginning in the 1960s and 1970s. In the beginning, accelerators were built for particle physics, and synchrotron radiation was used in "parasitic mode" when bending magnet radiation had to be extracted by drilling extra holes in the beam pipes.  The first [[storage ring]] commissioned as a synchrotron light source was Tantalus, at the [[Synchrotron Radiation Center]], first operational in 1968.<ref>E. M. Rowe and F. E. Mills, Tantalus I: A Dedicated Storage Ring Synchrotron Radiation Source, [http://cdsweb.cern.ch/record/1107919/files/p211.pdf Particle Accelerators], Vol. 4 (1973); pages 211-227.</ref>

Bending electromagnets in accelerators were first used to generate this radiation, but to generate stronger "brighter" radiation, other specialized devices – insertion devices – are sometimes employed. Innovations such as the [[Chasman–Green lattice]], an array of magnets which maximises brightness, led to a second-generation of dedicated light sources. The [[National Synchrotron Light Source]] at [[Brookhaven National Laboratory]] was the first to use such a lattice.<ref name="PhysicsWorld-Crease">{{cite web |last=Crease |first=Robert P |title=China’s High Energy Photon Source prepares to light up the world |website=Physics World |date=2025-03-25 |url=https://physicsworld.com/a/chinas-high-energy-photon-source-prepares-to-light-up-the-world/ |access-date=2025-05-20}}</ref>

Third-generation synchrotron radiation sources are typically reliant upon these insertion devices, where straight sections of the storage ring incorporate periodic magnetic structures (comprising many magnets in a pattern of alternating N and S poles – see diagram above) which force the electrons into a sinusoidal or helical path. Thus, instead of a single bend, many tens or hundreds of "wiggles" at precisely calculated positions add up or multiply the total intensity of the beam.{{Citation needed|date=January 2021}} These devices are called [[wiggler (synchrotron)|wiggler]]s or [[undulator]]s. The main difference between an undulator and a wiggler is the intensity of their magnetic field and the amplitude of the deviation from the straight line path of the electrons.{{Citation needed|date=January 2021}} The first third-generation light source, built with undulators as part of the initial design, the [[European Synchrotron Radiation Facility]] was opened to users in 1994.<ref name="PhysicsWorld-Crease" />

Fourth-generation sources, such as the [[Sirius_(synchrotron_light_source)|Sirius]]<ref name="PhysicsWorld-Crease" /> at the [[Laboratório Nacional de Luz Síncrotron|Brazilian Synchrotron Light Laboratory]] (LNLS), make use of "multi-bend achromat" magnets to further increase brightness of their electron beams.