synchrotron radiation, in physics, electromagnetic radiation electromagnetic radiation, energy radiated in the form of a wave as a result of the motion of electric charges. A moving charge gives rise to a magnetic field, and if the motion is changing (accelerated), then the magnetic field varies and in turn produces an
..... Click the link for more information. emitted by high-speed electrons spiraling along the lines of force of a magnetic field (see magnetism magnetism, force of attraction or repulsion between various substances, especially those made of iron and certain other metals; ultimately it is due to the motion of electric charges.
..... Click the link for more information. ). Depending on the electron's energy and the strength of the magnetic field, the maximum intensity will occur as radio waves, visible light, or X rays. The emission is a consequence of the constant acceleration experienced by the electrons as they move in nearly circular orbits; according to Maxwell's equations, all accelerated charged particles emit electromagnetic radiation. Although predicted much earlier, synchrotron radiation was first observed as a glow associated with protons orbiting in high-energy particle accelerators particle accelerator, apparatus used in nuclear physics to produce beams of energetic charged particles and to direct them against various targets. Such machines, popularly called atom smashers, are needed to observe objects as small as the atomic nucleus in studies
..... Click the link for more information. , such as the synchrotron. In astronomy, synchrotron radiation has been suggested as the mechanism for producing strong celestial radio sources like the Crab Nebula Crab Nebula, diffuse gaseous nebula in the constellation Taurus; cataloged as NGC 1952 and M1, the first object recorded in Charles Messier's catalog of nonstellar objects.
..... Click the link for more information. (see radio astronomy radio astronomy, study of celestial bodies by means of the electromagnetic radio frequency waves they emit and absorb naturally.

Radio Telescopes

..... Click the link for more information. ). Synchrotron radiation is employed in a host of applications, ranging from solid-state physics solid-state physics, study of the properties of bulk matter rather than those of the individual particles that compose it. Solid-state physics is concerned with the properties exhibited by atoms and molecules because of their association and regular, periodic
..... Click the link for more information. to medicine. As excellent producers of X rays, synchrotron sources offer unique probes of the semiconductors that lie at the heart of the electronics industry. Both ultraviolet radiation and X rays generated by synchrotrons are also employed in the treatment of diseases, especially certain forms of skin cancer.

synchrotron radiation

Electromagnetic radiation emitted by charged particles that are moving at speeds close to that of light when their paths are altered. It is so called because it is produced by high-speed particles in a synchrotron. Such radiation is highly polarized (see polarization) and continuous. Its intensity and frequency depend on the strength of the magnetic field that alters the path of the particles, as well as on the energy of those particles. Synchrotron radiation at radio frequencies is emitted by high-energy electrons as they spiral through magnetic fields in space, such as those around Jupiter. Synchrotron radiation is emitted by a variety of astronomical objects, from planets to supernova remnants to quasars.

Synchrotron radiation

Electromagnetic radiation emitted by relativistic charged particles curving in magnetic or electric fields. With the development of electron storage rings, radiation with increasingly high flux, brightness, and coherent power levels has become available for a wide variety of basic and applied research in biology, chemistry, and physics, as well as for applications in medicine and technology. See Electromagnetic radiation, Particle accelerator, Relativistic electrodynamics

Electron storage rings provide radiation from the infrared through the visible, near-ultraviolet, vacuum-ultraviolet, soft-x-ray, and hard-x-ray parts of the electromagnetic spectrum extending to 100 keV and beyond. The flux [photons/(second, unit bandwidth)], brightness (or brilliance) [flux/(unit source size, unit solid angle)], and coherent power (important for imaging applications and proportional to brightness) available for experiments, particularly in the vacuum-ultraviolet, soft-x-ray, and hard-x-ray parts of the spectrum, are many orders of magnitude higher than is available from other sources.

The radiation has many features (natural collimation, high intensity and brightness, broad spectral bandwidth, high polarization, pulsed time structure, small source size, and high-vacuum environment) that make it ideal for a wide variety of applications in experimental science and technology. Very powerful sources of synchrotron radiation in the ultraviolet and x-ray parts of the spectrum became available when high-energy physicists began operating electron synchrotrons in the 1950s. Although synchrotrons produce large amounts of radiation, their cyclic nature results in pulse-to-pulse intensity changes and variations in spectrum and source shape during each cycle. By contrast, the electron-positron storage rings developed for colliding-beam experiments starting in the 1960s offered a constant spectrum and much better stability. Beam lines were constructed on both synchrotrons and storage rings to allow the radiation produced in the bending magnets of these machines to leave the ring vacuum system and reach experimental stations. In most cases the research programs were pursued on a parasitic basis, secondary to the high-energy physics programs.

Since about 1980, fully dedicated storage ring sources have been completed in several countries. They are called second-generation facilities to distinguish them from the first-generation rings that were built for research in high-energy physics.

Special magnets may be inserted into the straight sections between ring bending magnets to produce beams with extended spectral range or with higher flux and brightness than is possible with the ring bending magnets. These devices, called wiggler and undulator magnets, utilize periodic transverse magnetic fields to produce transverse oscillations of the electron beam with no net deflection or displacement. They provide another order-of-magnitude or more improvement in flux and brightness over ring bending magnets, again opening up new research opportunities. However, their potential goes well beyond their performance levels, in first- and second-generation sources.

Third-generation sources are storage rings with many straight sections for wiggler and undulator insertion device sources and with a smaller transverse size and angular divergence of the circulating electron beam. The product of the transverse size and divergence is called the emittance. The lower the electron-beam emittance, the higher the photon-beam brightness and coherent power level. With smaller horizontal emittances and with straight sections that can accommodate longer undulators, third-generation rings provide two or more orders of magnitude higher brightness and coherent power level than earlier sources.

One consequence of the extraordinary brilliance of these sources is that the x-ray beam is partially coherent. By aperturing the beam, a fully coherent beam can be obtained, but at the expense of flux. Nonetheless, there is still sufficient flux remaining to explore the use and application of coherent x-ray beams. See Coherence

Several third-generation rings are in operation. Low-energy (typically 1–2-GeV) third-generation rings (see illustration) are optimized to produce high-brightness radiation in the vacuum ultraviolet (VUV) and soft x-ray spectral range, up to photon energies of about 2–3 keV. High-energy rings (typically 6–8 GeV) aim at harder x-rays with energies of 10–20 keV and above.

Layout of the 1

The radiation produced by an electron in circular motion at low energy (speed much less than the speed of light) is weak and rather nondirectional. At relativistic energies (speed close to the speed of light) the radiated power increases markedly, and the emission pattern is folded forward into a cone with a half-opening angle in radians given approximately by γ - 1 = mc²/E, where mc² is the rest-mass energy of the electron (0.51 MeV) and E is the total energy. Thus, at electron energies of the order of 1 GeV, much of the very strong radiation produced is confined to a forward cone with an instantaneous opening angle of about 1 mrad (0.06°). At higher electron energies this cone is even smaller. The large amount of radiation produced combined with the natural collimation gives synchrotron radiation its intrinsic high brightness. Brightness is further enhanced by the small cross-sectional area of the electron beam, which is as low as 0.01 mm² in the third-generation rings.