Synchrotron radiation

Synchrotron radiation is known as the electromagnetic radiation which is emitted tangentially to the movement direction of charged particles, as they move with relativistic speed and be deflected from a straight path. Since the deflection in the physical sense is an acceleration (change of velocity vector ), is a special form of bremsstrahlung.

Generation

Synchrotron radiation is produced for applications by deflection of electrons with kinetic energies of the order of 1 giga-electron volts ( GeV ). These are electron storage rings and free-electron laser with specially designed magnetic structures ( undulators ). In astronomy, synchrotron radiation occurs when a hot plasma moving in a magnetic field. Examples of cosmic synchrotron sources are pulsars, radio galaxies and quasars.

The energy loss of a particle with the charge through the radiation is, for example in a storage ring per revolution

Here, the atomic number, the elementary charge, the electric field is constant, the radius of the storage ring, the ratio of the particle to the speed of light and the Lorentz factor.

For relativistic speeds, so and so, this becomes:

At speeds near the speed of light so does the energy loss of the particle by the radiation to very steep with the kinetic energy. It is also clear why for synchrotron radiation sources is always the lightest charged particles are used: Due to the smaller mass of the energy radiated by electrons and positrons compared to the lightest ions, protons, by 13 orders of magnitude higher.

The opening angle in which the synchrotron radiation is concentrated to the current direction of flight of the particle around decreases with increasing energy of the particle and is given by

In the rest frame of the emission current is based on the characteristic of a Hertzian dipole transverse to the acceleration of the particle. The system in the laboratory with increasing energy observed increasingly sharp focusing along the direction of movement may be understood by the Lorentz transformation.

For the generation of synchrotron radiation, there are about 30 laboratories worldwide. In Germany, among others BESSY in Berlin, DESY in Hamburg, ELSA at Bonn University, DELTA at the Technical University of Dortmund and ANKA in Karlsruhe. A natural source of synchrotron radiation in space, for example, of Jupiter, its moons, bombards with this type of radiation.

Properties

Synchrotron radiation has a number of interesting properties for application in science and technology:

  • Very broad, continuous spectrum from the infrared through the visible spectral range, from ultraviolet to deep in the field of X- radiation
  • High radiant intensity compared to other radiation sources other than lasers,
  • The radiation passes bundled tangentially to the movement direction of the particles
  • Depending on the quality of the electron beam a very high brilliance
  • It is pulsed, the repetition rate and duration are adjustable ( within narrow limits )
  • Exact predictability of the emitted spectrum, making it suitable as a radiation standard for the calibration of radiation sources or detectors
  • The radiation is coherent, which provides the basis for the free-electron laser ( FEL)
  • The radiation is polarized linearly in the plane of the synchrotron, below and above a more or less elliptic

Polarization of the synchrotron radiation

The linearly polarized in the direction of the ring plane radiation is good example to characterize magnetic materials by means of micromagnetic investigation. The linear polarization can be converted by means of mechanical phase shift of the magnetization regions in an undulator in circular polarization; This allows higher contrast at the investigation of the magnetization regions of magnetic materials. The irradiation of racemic organic compounds with circularly polarized synchrotron radiation allows about to achieve an enantiomeric excess in chiral amino acids.

Brilliance differences

A distinction is made of the first, second, third and fourth generation sources. They differ mainly by the brilliance of the emitted radiation.

  • In the first-generation particle accelerator particle physics " parasitic" used.
  • In the second generation synchrotron radiation sources are built solely to produce the radiation, while it saves the accelerated particles for several hours in storage rings, thus achieving constant working conditions. The generation of the radiation takes place in special magnetic structures, the dipole magnets and wigglers.
  • The third generation synchrotrons form with undulators in the storage ring. With a brilliant undulator radiation can be generated than with wigglers.
  • Free-electron laser (FEL ) represent the fourth generation dar. first plants are FELICITA on DELTA at the TU Dortmund and the FLASH at DESY in Hamburg.

Use

The synchrotron radiation can be used for the

  • Surface Physics
  • Materials Science
  • X-ray diffraction
  • Photochemistry
  • X-ray lithography
  • Metrology
  • Mineralogy
  • Molecular Biology
  • Biophysics and
  • Medicine

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