European x-ray free electron laser

The European x-ray free electron laser (XFEL) is a planned European project in strong connection with the DESY research center in Hamburg. [cite web |title=XFEL|url=http://xfel.desy.de/ |format= |accessdate=2007-12-20] . A free electron laser generates high intensity electromagnetic radiation (in this case x-rays) by accelerating electrons to relativistic speeds. The XFEL is constructed such that the electrons produce x-ray light in synchronisation resulting in high-intensity x-ray pulses with the properties of laser light with intensities much brighter than that produced by conventional synchrotron light sources.

Location

The XFEL is planned to run 3.4 km underground from the DESY site, in the quarter Bahrenfeld of Hamburg, to the town of Schenefeld where a new XFEL research facility is to be constructed.

The accelerator

Electrons will be accelerated to an energy of 10-20 GeV by a 2.1 km long superconducting linear accelerator. The electrons are then introduced into the magnetic fields of undulators where they undergo curved trajectories resulting in the emission of x-ray radiation.

The Laser

In contrast to current x-ray light sources the x-ray light will be generated by Self Amplified Spontaneous Emission (SASE) whereby the electrons interact with the radiation that they or their neighbours emit. The result is the spontaneous emission of tightly bunched packages of radiation which are amplified like laser light. The peak brilliance of the XFEL will be billions of times higher than that of conventional X-ray light sources, with its average brilliance 10,000 times higher. [cite web |title=XFEL Project information|url=http://xfelinfo.desy.de/en/artikel.xfel-zahlen-und-fakten/2/index.html |format= |accessdate=2007-12-20] The proposed facility will also produce many more pulses per second than similar projects in the USA and Japan, which is achieved by adopting the superconducting linear accelerator technology developed at DESY. [cite web |title=Diamond webpages| url=http://www.diamond.ac.uk/ForUsers/SRUser07/MassimoAltarelli.htm |format= |accessdate=2007-12-21]

Research

The duration of the light pulses will be less than 100 femtoseconds making it possible to measure chemical reactions that are too rapid to be captured by different methods. The wavelength of the X-ray laser may be varied from 0.085 to 6 nanometers enabling measurements at the atomic length scale.

Initially, 3 photon beamlines with 6 experimental stations (later to be upgraded to 5 photon beamlines and 10 experimental stations) are foreseen. The proposed experimental beamlines will enable unique scientific experiments exploiting the high intensity, coherence and the time structure of the new source to be conducted in a variety of disciplines spanning physics, chemistry, materials science, biology and nanotechnology.

Commisioning

The German Federal Ministry of Education and Research granted permission to build the facility in February 2003 at a cost of 986 million Euro. [cite web |title=XFEL info|url=http://xfelinfo.desy.de/en/artikel.xfel-zahlen-und-fakten/2/index.html|accessdate=2007-12-21] Following a construction period of 6.5 years, the commissioning of the facility should begin in 2013. [cite web |title=Hasylab| url=http://hasylab.desy.de/facilities/xfel_project/index_eng.html| format= |accessdate=2007-12-21]

Current status

In 2007, the XFEL project was officially launched [cite web |title=Launch of XFEL|url=http://www.xfel.eu/XFELpresse/en/pressemeldungen/2007-06-05/index.html] . As a first stage, a reduced version will become operational which reduces the initial costs to 850 million Euro. In difference to the original design, the reduced version has no beamlines for hard x-rays (20-100 keV photon energy). Furthermore, the existing undulators have been partly limited in functionality (e.g. fixed instead of variable wavelength), and the maximum energy of the accelerator has been lowered.

The XFEL GmbH that will build and run the facility is to be founded in spring/summer 2008. Immediately afterwards, the construction is planned to begin.

References