PETRA III, which took up operation in 2009, is the most brilliant storage-ring-based X-ray radiation source in the world. As the most powerful light source of its kind, it offers scientists outstanding experimental opportunities with X-rays of an exceptionally high brilliance. In particular, this benefits researchers investigating very small samples or those requiring tightly collimated and very short-wavelength X-rays for their experiments.

The world's best light source of its kind

The PETRA accelerator originally served for particle physics experiments, then as a pre-accelerator for the large HERA facility. After the shutdown of HERA in 2007, DESY converted the PETRA ring within only two years into the world's best storage-ring-based X-ray radiation source. To achieve this, nearly 300 metres of the 2.3-kilometre-long ring accelerator were completely rebuilt and a new experimental hall was constructed.

In its final stage, PETRA will feature 14 experimental stations with up to 30 instruments. Excellent experimental capabilities are ensured by the installation of undulators – long arrays of magnets that generate X-ray radiation of exceptionally high brilliance. In simple terms, this means that a very large number of photons are emitted from a very small area to form an extremely collimated beam of X-rays. As a result, PETRA III delivers a photon flux within an area of a single square millimetre that is as high as DORIS III produces on several square centimetres.

Excellent outlook for research

A hair-thin, brilliant X-ray beam such as the one produced by PETRA III gives researchers vital advantages. For example, even minuscule material samples can be studied and the arrangement of their atoms precisely determined – or molecular biologists can explore the atomic structure of tiny protein crystals. The demand for such information is enormous. The structure of proteins generated according to the genetic blueprint is at the very top of the researchers’ wish list. An important application is the development of new drugs that can be targeted precisely at the location where a pathogen attacks.

Because of this excellent outlook, the European Molecular Biology Laboratory (EMBL) and DESY are extending their collaboration, which has already endured more than 30 years, to cover PETRA III as well. The Hamburg outstation of the EMBL constructed EMBL@PETRA III, an integrated research facility for structural biology at DESY. Its state-of-the-art experimental stations enable researchers to utilize the extraordinary properties of the storage ring for innovative applications in the life sciences – for example, to make advances in protein crystallography, small-angle X-ray scattering and X-ray absorption spectroscopy of biological materials. In the new facility, all the steps involved – from high-throughput protein crystallization and sample preparation to data processing – can be performed under one roof. This advance will decidedly speed up the research on molecules that make the difference between human health and disease.

PETRA III also opens many different opportunities in the field of materials research. For certain applications, materials researchers need highly energetic photons with high penetration power – for example, to test welding seams or to check production parts for signs of fatigue. The PETRA III storage ring generates especially high-energy radiation at up to 100 000 electron volts with high brilliance – a decisive advantage for many experiments.

Research examples

The challenge of structural biology

To decode and understand the building blocks of life, ever larger and more complex molecules are now being studied – whose crystals diffract X-rays less and less. A prime example is the exploration of the ribosome. The more complex the structure, the more intense must be the X-rays used to examine it. The big challenge of the future is to explore the way a complete cell operates at the molecular level. Modern synchrotron radiation sources such as PETRA III make important contributions in this quest.

New materials in 3D

In recent decades, computed tomography has become an established technique in the materials sciences too, and a standard method for the examination of inner structures of materials. Spatial resolution and image contrast in particular have been continuously improved. The high-brilliance X-rays from PETRA III make it possible to study structures in different materials with an accuracy of less than one micrometre in high-speed exposures. As a result, even fast process sequences, such as foam formation, can be studied in serial 3D images. Special contrast techniques can be used to visualize even low-contrast objects three-dimensionally and non-destructively, and to analyse them quantitatively. As an example, X-ray microtomography can be used to study the integration of cells into biocompatible materials non-destructively, and thus to gain knowledge about the best way to create 3D cellular substrates.

Chemical analyses on a microscopic scale

The optical microscope enables scientists to view the microcosm. But as a rule it doesn’t reveal which chemical elements the visualized structures comprise. Focused X-rays at PETRA III provide the capability of chemically analysing a sample on a very small scale. This method produces three-dimensional microscopic images of the element distribution – even when less than one in a million particles consists of the element in question. It is also possible to visualize chemical bonds and crystal structures. This method is non-destructive and fast, so that even growth processes can be studied. These capabilities are important in many diverse applications in biomedicine, environmental analysis and materials sciences.

Such methods were for instance useful in studying the magnetic sense of birds. In the past it was impossible to seperately study the crystals involved in this phenomenon, which are composed of two different iron compounds. But the focused X-ray beams at PETRA III are so fine that the different crystals can be individually measured to gain an even better understanding of the magnetic sense in birds.

Nanomagnets for data storage

Ultra-thin magnetic films have become indispensable when more data must be stored in ever less space. The magnetic storage density of commercially available hard disks presently makes it possible to store and play full-length movies on devices the size of a credit card. This property is physically based on magnetic structures that are 10 000 times smaller than the diametre of a human hair. The stored information is contained in the orientation of tiny, closely packed nanomagnets. In writing information on such storage media, it must be possible to change this orientation in an instant without influencing neighbouring nanomagnets. The way this process unfolds depends on what these structures are made of. To further develop and optimize these types of storage media, scientists must therefore be able to view the inside of such nanostructures. This becomes possible with the highly brilliant X-rays of PETRA III.

Tailor-made surfaces

Focused X-rays at PETRA III are up to 1000 times finer than a human hair. Such nanobeams create many entirely new opportunities for studying materials, especially surfaces.

In many cases, the microstructure of surfaces determines their properties and function. Examples include water- and dirt-repellent coatings, catalytic surfaces and materials whose optical properties can be precisely selected by placing tiny, nanometre-sized particles of noble metals on the surface. The shape and arrangements of these particles determine the colour and brightness of the surface in visible light. This technique can, for example, be used to create forgery-proof identification. The nanobeams of PETRA III enable scientists to determine the structure and arrangement of such particles on surfaces with great precision. What’s more, it becomes possible to watch and understand the creation, growth and distribution of nanoparticles on surfaces in real technical production processes – an important requirement in the pursuit of further improvements of these methods.