FLASH restarted the forth user period after successful exchange of the
RF gun

 
In June 2012, the fourth user period has been interrupted by a failure of the RF gun. Thanks to the effective and fast work of the DESY support teams in Hamburg and Zeuthen, the RF gun has been quickly exchanged within 2 weeks only and is now running better than ever.
Recently, 5000 FEL pulses per second have been produced with a record average FEL radiation power of 400 mW delivered to a user experiment.
The fourth user period started March 2012 and will continue until February 2013 with 3800 h of scheduled beam time.

FLASH, the world's first soft X-ray free-electron laser is available to the photon science user community for experiments since 2005.

The accelerator is equipped with seven TESLA-type 1.3 GHz superconducting accelerator modules yielding an electron beam energy of up to 1.25 Gigaelectron volts (GeV). A special 3.9-GHz module built at Fermilab is installed to improve the quality of the accelerated electron bunches. The so-called third harmonic cavities show excellent results: the 3.9-GHz module shapes the electron bunches in a way that the intensity of the laser light is higher than ever before.
In September 2010, the FLASH accelerator team operated the FEL with an electron energy of 1.25 Gigaelectron volts reaching a wavelength of 4.12 nanometres. For the first time FLASH has generated laser light in the so-called water window with the fundamental wavelength – so far this was only reached with higher harmonics.
The water window is a wavelength region between 2.3 and 4.4 nanometres. In the water window, water is transparent for light, i.e. it does not absorb FEL light. This opens up the possibility to investigate samples in an aqueous solution. This plays an important role especially for biological samples, because carbon atoms in these samples are highly opaque to the X-ray radiation, while the surrounding water is transparent and therefore not disturbing.
 
In April 2012, sFLASH, the seeding experiment at FLASH, has obtained first seeding at 38 nm. An external seed source of the same wavelength overlaps with the electron beam to seed the SASE process in a series of undulators installed between the accelerator and the FLASH undulators.

FLASH layout as pdf (37KB)

 

Many scientific disciplines ranging from physics, chemistry and biology to material sciences, geophysics and medical diagnostics use
the powerful soft X-ray source FLASH. The ultra-short X-ray pulses in the femtosecond range allow experiments which are not possible otherwise. For example, time-resolved observation of chemical reactions with atomic resolution, single shot diffraction imaging, and many others.
More than 160 publications on photon science have been published already, many in high ranked journals.

FLASH is a high-gain free-electron laser (FEL) which achieves laser amplification and saturation within a single pass of the electron
bunch through a long undulator section. The lasing process is initiated by the spontaneous undulator radiation. The FEL works in the so-called Self-Amplified Spontaneous Emission (SASE) mode without needing an external input signal.The electron bunches are produced in a laser-driven photoinjector and accelerated by a superconducting linear accelerator. The RF-gun based photoinjector allows the generation of electron bunches with tiny emittances - mandatory for an efficient SASE process.The superconducting techniques allows to accelerate thousands of bunches per second, which is not possible with other technologies. At intermediate energies of 150 and 450 MeV the electron bunches are longitudinally compressed, thereby increasing the peak current from initially 50-80 A to 1-2 kA - as required for the lasing process in the undulator. The 27 m long undulator consists of permanent NdFeB magnets with a fixed gap of 12 mm, a period length of 27.3 mm and peak magnetic field of 0.47 T. The electrons interact with the undulator field in such a way, that so called micro bunches are developed. These micro bunches radiate coherently and produce intense X-ray pulses. Finally, a dipole magnet deflects the electron beam safely into a dump, while the FEL radiation propagates to the experimental hall.

Picture gallery of the FLASH linac