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Synchrotron Radiation & Storage Rings

Each accelerated charge radiates, described by fundamental laws of electrodynamics, electromagnetic waves. These electromagnetic waves, generated as a result of acceleration (e.g. the horizontal one in a storage ring), are called synchrotron radiation. The naming is for historical reasons, since the first accelerator, where this radiation was observed, was a so called synchrotron. Although already predicted the in the beginning of the last century, synchrotron radiation was not proved until the end of 1940 years. It was done both, indirectly – by measuring the energy loss of relativistic electrons in an accelerator - and directly - by visual observation.

In the “First Generation Light Sources” synchrotron radiation from accelerator facilities of high energy physics was used parasitically, where it was produced as an undesired side effect, counteracting the intended acceleration.

With the first successful storage of electrons in a rings the basis for a new generation of synchrotron radiation sources had been created. In the early 1970’s first dedicated storage rings were build, exclusively constructed to generate synchrotron radiation. BESSY I, a Soft VUV facility, operated from 1980 – 1999 in Berlin Wilmersdorf, was one of these “Second Generation Synchrotron Sources”

While in these sources synchrotron radiation was produced in the beam-guiding dipole magnets only, the development of special magnet structures, the so-called “Insertion Devices” (ID), begun. These ID’s produce more intense light or shift the synchrotron light spectrum towards higher photon energies.

From the early 90’s, “Third Generation Synchrotron Radiation Sources” have been put into operation, producing highly brilliant radiation and specially optimized for the use of insertion devices. BESSY II, operated since 1999, is one example.

The synchrotron radiation, generated in the storage rings, has a number of attractive properties, which makes them in its entirety almost superior to any other source of radiation:

• Intense, precisely calculable radiation over a wide range,
• strongly forward focused radiation with small source area,
• radiation in the ring plane linear, surface and polarized below circular,
• pulsed radiation, according to the time structure of the electron beam,
• clean source: created in ultra-high vacuum, so that no contamination of the sample has to be feared and the use of vacuum windows can be surrendered.

These properties make synchrotron radiation to one of the most important, universal research tools, with a steadily increasing number of users. It finds application in all scientific areas, from physics, chemistry and biology to human medicine and industrial applications (lithography, materials research).

Fig.: Properties of Synchrotron Radiation

Fig.: One of the BESSY II Insertion Devices (Type: Undulator)