Research with synchrotron radiation

Properties - research fields - grand challenges - applications

Research with synchrotron radiation and its applications

 Synchrotron radiation light gives us a better understanding of the material world. It provides insight into the microscopic structure of materials and the relationship between structure and function. This knowledge is essential for tackling the key challenges of our time. We search for solutions for clean and affordable energy, environment protection, health and well-being, as well as information and data science where tailored materials are at the heart of a sustainable future.

What is synchrotron radiation?

In light sources, we make use of the fact that when charged particles are accelerated, they emit light (radiate). If electrons are accelerated back and forth in an antenna at kilohertz or Megahertz frequencies they radiate in the radio or TV portions of the electromagnetic spectrum. If electrons that are moving with nearly teh velocity of light (v=0.9c) are constrained to move in a curved path (circles, spirals, and undulations are examples) they will be accelerating toward the inside of the curve and will also radiate what we call synchrotron light or synchrotron radiation.

Synchrotron light of this type occurs naturally in the distant reaches of outer space. For example, magnetic fields are found throughout the Milky Way, such as the striking galactic center radio arc, comprising filamentary structures whose radio-wave emission spectra suggest the filaments are produced by synchrotron radiation from relativistic electrons spiraling around a magnetic field.

Accelerator-based synchrotron light was seen for the first time at the General Electric Research Laboratory in the USA in 1947 in a type of accelerator known as a synchrotron. First considered a nuisance because it caused the particles to lose energy, it recognized in the 1960s as light with exceptional properties. The light produced at today’s light sources is very bright. In other words, the beam of x rays or other wavelengths is as thin as a hair and very intense. Just as laser light is much more intense and concentrated than the beam of light generated by a flashlight, so an x-ray beam produced by a synchrotron is a trillion times brighter than the beam produced by a hospital x-ray machine whose x-ray tubes emit light over a wide angle and with high intensity only at particular wavelengths. Synchrotron radiation is polarised and pulsed, and the frequency and duration of the pulses can be manipulated to a certain extent, see figure.

To produce synchrotron radiation in the lab, one does actually not use the synchrotron, but storage rings. While the charged particles are accelerated further in a synchrotron, in a storage ring only the energy loss is balanced out to keep the energy of the particle beam and thus the energy spectrum of the synchrotron radiation constant. A newer development is the Free-Elektronen-Laser (FEL), which also produces synchrotron radiation. Worldwide there exist about 30 laboratories for the production of synchrotron radiation. In Germany those are amongst others BESSYII at HZB in Berlin, PETRAIII and FLASH at DESY in Hamburg, European XFEL in Hamburg and Schenefeld, the electron-stretching-device in Bonn, DELTA at Dortmund University and KIT Light Source in Karlsruhe.

Sources: Wikipedia /


What is a free-electron laser (FEL)?

The free-electron laser (FEL) is a synchrotron radiation source that generates coherent radiation of very high brilliance. Coherent radiation is defined as radiation whose components (wave packets) oscillate in fixed relationships to one another. Because of the coherence of the radiation, the FEL is called a laser. In principle, free-electron lasers cover large parts of the spectral range, but they are optimized for a certain range. For example, the Particle Physics Lab FEL in Dubna operates in the millimetre range, the FLASH (free-electron laser in Hamburg) at DESY in the UV range (6 to 30 nm) and the European XFEL in Schenefeld and Hamburg cover the X-ray range down to 0.05 nm. Such free-electron lasers are often referred to as X-ray lasers.

The first part of a free-electron laser consists of a particle accelerator in which electrons are accelerated to almost the speed of light. In the second part, the electrons are brought onto a slalom course in special magnetic field arrangements (so-called undulators) and emit radiation in the process. FELs have this structure in common with conventional modern synchrotron radiation sources. The trick in an FEL is to allow the electrons to interact on their way through the magnetic field of the undulator with radiation that has exactly the same wavelength as the radiation emitted by the electrons. The result is an FEL that shines many times more intensely.

The microbunching effect ensures that the electron bunch is microstructured by the interaction with the generated laser radiation. The electron bunch is structured into thin slices that are aligned perpendicular to the direction of flight. These slices have a distance exactly aligned to the radiation, which is equal to the wavelength, so that all electrons in the packet can radiate coherently at the same time.

The wavelength of an FEL can be tuned by varying the energy of the electrons. Modern FELs deliver coherent high-intensity radiation up to the X-ray range.

Sources: Wikipedia / Welt der Physik



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