Photon Beam Transport System

From the source towards the experiments

The User Facility

The FLASH experimental hall starts 30 meters behind the last dipole magnet that separates the electron bunches and the photon beam emerging from the long undulator in the accelerator tunnel. The photon beam transport system in the hall delivers the FEL pulses – as short as few 10 fs – to the experimental stations.

The Photon Beam Transport System

The femtosecond FEL pulses emerge from the undulator in the accelerator tunnel and can be delivered to five experimental stations by the photon beam transport system operating under high vacuum conditions. In order to mak­e efficient use of the FEL radiation, it can be steered to different experimental stations just by switching one or two plane mirrors by remote control. However, presently only one experimental station can be served at a time.

The FEL pulses are switched between the beamlines by 0.5-m-long plane mirrors reflecting the beam at grazing incidence angles of two and three degrees. The FEL optics system has been designed to avoid the risk of damage due to the immense peak powers and to minimize deformation of the mirrors at long bunch trains, i.e. high average power. The mirrors consist of cooled silicon substrates with high-density carbon coatings, which are superior to other materials in the spectral range of FLASH. These coatings are characterized by a high reflectivity between 94 and 96 percent for energies below 200 eV, and a low surface roughness of less than 0.5 nm over the full mirror length.

In the accelerator tunnel and in the photon beam distribution system in the experimental hall a suit of photon diagnostics and beam manipulation tools are incorporated into the beamlines. Details are found here.