Undulator

Undulator

An undulator is an insertion device from high-energy physics and usually part of a larger installation, a synchrotron storage ring. It consists of a periodic structure of dipole magnets (see dipole magnet). The static magnetic field is alternating along the length of the undulator with a wavelength lambda_u. Electrons traversing the periodic magnet structure are forced to undergo oscillations and radiate. The radiation produced in an undulator is very intense and concentrated in narrow energy bands in the spectrum. It is also collimated on the orbit plane of the electrons. This radiation is guided through beamlines for experiments in various scientific areas.

The important dimensionless parameter

K=frac{e B lambda_u}{2 pi m_e c},

where "e" is the particle charge, "B" the magnetic field, "m_{e}" the electron rest mass and "c" the speed of light, characterizes the nature of the electron motion. For Kll1 the oscillation amplitude of the motion is small and the radiation displays interference patterns which lead to narrow energy bands. If Kgg1 the oscillation amplitude is bigger and the radiation contributions from each field period sum up independently, leading to a broad energy spectrum. In this regime of fields the device is no longer called an "undulator"; it is called a wiggler.

The usual description of the undulator is relativistic but classic. This means that though the precision calculation is tedious the undulator can be seen as a black box. An electron enters this box and an electromagnetic pulse exits through a small exit slit. The slit should be small enough such that only the main cone passes, so that the side lobes may be ignored.

Undulators can provide several orders of magnitude higher flux than a simple bending magnet and as such are in high demand at synchrotron radiation facilities. For an undulator with N periods, the brightness can be up to N^{2} more than a bending magnet. The intensity is enhanced up to a factor of N at harmonic wavelengths due to the constructive interference of the fields emitted during the N radiation periods. The usual pulse is a sine with some envelope. The second factor of N comes from the reduction of the emission angle associated with these harmonics, which is reduced as 1/N. When the electrons come with half the period, they interfere destructively, the undulator stays dark. The same is true, if they come as a bead chain.

The polarization of the emitted radiation can be controlled by using permanent magnets to induce different periodic electron trajectories through the undulator. If the oscillations are confined to a plane the radiation will be linearly polarized. If the oscillation trajectory is helical, the radiation will be circularly polarized, with the handedness determined by the helix.

If the electrons follow the Poisson distribution a partial interference leads to a linear increase in intensity.In the free electron laser the intensity increases exponentially with the number of electrons.

An undulator's figure of merit is spectral radiance.

External links

D. T. Attwood's page at Berkeley: [http://www.coe.berkeley.edu/AST/sxreuv/ Soft X-Rays and Extreme Ultraviolet Radiation] . His lecture and viewgraphs are available online.


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Look at other dictionaries:

  • Undulator — von Lauritzen, s. Telegraph, S. 443 …   Lexikon der gesamten Technik

  • Undulator —   der, s/. .. oren, Physik: Wiggler. * * * Un|du|la|tor, der; s, ...oren: Instrument zur Aufzeichnung empfangener Morsezeichen bei langen Telegrafenkabeln …   Universal-Lexikon

  • Undulator — Ein Undulator (englisch: to undulate = sich schlängeln, wellenförmig bewegen) oder Wiggler (to wiggle = wackeln) ist ein technisches Gerät zur Erzeugung von Synchrotronstrahlung. Es wird als so genanntes Insertion device in Teilchenbeschleunigern …   Deutsch Wikipedia

  • Undulator — onduliatorius statusas T sritis radioelektronika atitikmenys: angl. undulator vok. Undulator, m rus. ондулятор, m pranc. ondulateur, m …   Radioelektronikos terminų žodynas

  • undulator — onduliatorius statusas T sritis radioelektronika atitikmenys: angl. undulator vok. Undulator, m rus. ондулятор, m pranc. ondulateur, m …   Radioelektronikos terminų žodynas

  • undulator — I. ˈ ̷ ̷ ̷ ̷ˌlād.ə(r), ātə noun ( s) : one that undulates a lovely blonde lady undulator Wall Street Journal II. noun : a device consisting of a series of magnetic dipoles of alternating polarity into which a stream of particles (as electrons)… …   Useful english dictionary

  • undulator — noun A periodic structure of dipole magnets that generates a low energy collimated beam of radiation …   Wiktionary

  • Undulator — Un|du|la|tor der; s, ...oren <zu ↑...ator> früher verwendetes Instrument zur Aufzeichnung empfangener Morsezeichen bei langen Telegrafenkabeln (z. B. Seekabel) …   Das große Fremdwörterbuch

  • undulator — un·du·la·tor …   English syllables

  • undulate — undulator, n. v. /un jeuh layt , un dyeuh , deuh /; adj. /un jeuh lit, layt , un dyeuh , deuh /, v., undulated, undulating, adj. v.i. 1. to move with a sinuous or wavelike motion; display a smooth rising and falling or side to side alternation of …   Universalium

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