By Jonathan Amos Science reporter, BBC News

The XFEL will start in a chamber more than 30m underground

A major new particle accelerator is to be built at Hamburg, Germany, that is capable of producing super-brilliant, ultra-short flashes of X-ray light.

The intense beam made in the 3.4km-long (2.1 miles) machine will probe how matter is pieced together atom by atom.

The properties of the X-ray Free-Electron Laser (XFEL) should make it possible, for example, to film the very moment a chemical reaction occurs.

Construction of the 986m euro (£668m) facility will begin later this year.

It will be placed underground. The XFEL will begin on the DESY (Deutsches Elektronen-Synchrotron) site in Hamburg and then run north-west, fanning out to experimental stations close to the neighbouring town of Schenefeld.

Electron wiggle

Scientists from academia and industry across the world are expected to apply for time on the facility when it becomes operational in 2013.

The linear accelerator will run for 3.4km

The insights they gain are expected to lead to a raft of discoveries across biology, chemistry, physics and Earth sciences.

"This will be a fundamental research tool that is needed, for example, to make advances in the pharmaceutical industry and in the domain of new materials, in particular nano-materials," explained Professor Massimo Altarelli, the XFEL project team leader.

"It will also lead to a lot of advances in plasma physics, in high-energy density matter because its pulses generate plasmas in conditions that you cannot generate any other way. This is relevant for astrophysics and for understanding fusion for energy production," he told BBC News.

The first part of the XFEL consists of a particle accelerator in which bunches of electrons are taken to almost the speed of light, before being thrown down a slalom course controlled by a long system of magnets known as undulators.

As the electrons bend and turn, they emit flashes of X-rays; and as the particles interact with the radiation, they also bunch even tighter.

Their compact configuration not only intensifies their light emission but gives it coherence as well. In essence, the X-rays are "in sync" and have the properties of laser light.

Getting depth

The peak brilliance of the linear XFEL should be a billion times greater than current X-ray light sources that use a ring configuration - such as the European Synchrotron Radiation Facility (ESRF) at Grenoble, France; or the recently opened Diamond Light Source at Harwell, UK.

The detected X-ray pattern reveals the target's internal structure

The principles of investigation, though, are much the same. As the X-rays pass through matter, their paths change and this gives clues to the atomic arrangement of the material under study.

The XFEL should produce flashes of light that last less than 100 quadrillionths of a second (100 femtoseconds). This is the timescale of molecular movement, which will make it possible to film chemical reactions without any blurring of the image.

In addition, because the flashes have the properties of laser light, it should be possible to do holography - to capture three-dimensional images of molecules.

"The brilliance of the free-electron laser gives us the hope that we will be able to get an X-ray diffraction pattern for a single macromolecule like a protein, so that you don't need to crystallise the protein to deduce its atomic structure," said Professor Altarelli.

"Crystallisation is actually impossible for a vast class of proteins, notably cell membrane proteins. That's a major roadblock in structural biology that the XFEL will hopefully overcome."

Lighting up the future

The XFEL is one of the major projects listed on a roadmap of research infrastructures that Europe feels it needs to fulfil its scientific goals over the next 20 years. These range from high-performance computing systems through to a plan to construct the world's biggest telescope.

An undulator is a special arrangement of magnets

As such, the XFEL is being built with money from across the continent - but it is Germany as the host which will bear most of the cost.

On Tuesday, bureaucrats and scientists from EU member states met in Hamburg to formally launch the linear accelerator project.

Although not all the 986m euros have been committed, sufficient funds are now available to construct a fully working facility. It is expected more money will come at a later date to develop the project to slightly higher energies and provide more experimental stations.

The UK is still assessing - and negotiating - the terms of its membership. A sum of about £30m (via the Large Facilities Capital Fund) has been reserved for the XFEL.

Britain would probably give some of this in a cash payment but the greater part of its contribution would be in-kind, providing technologies such as detectors.

Professor Robert Donovan is currently conducting a review for the UK's Science and Technology Facilities Council that will help determine on what basis Britain gets involved in so called fourth-generation light sources.

The US and Japan have designs of their own, but Professor Donovan told BBC News: "The XFEL is the next big step forward. The Germans are leading in a lot of technological areas and we would be joining the number one team in the world in terms of building X-ray free-electron lasers."

At the head of the XFEL, bunches of electrons are first sped up to near-light-speed in a super-cold, vacuumed accelerator The particles are directed down long undulators - magnetic systems that produce a slalom course for the electrons As they wiggle back and forth in the undulators, the fast-moving electrons emit very bright X-rays flashes The particles interact with this great sea of X-rays and begin to organise themselves into even tighter groupings This intensifies the brilliance of their emission and gives it coherence - the X-rays are "in sync" and laser-like Having done their job, the electrons are siphoned off, leaving the X-ray flashes to hit their experimental targets