InternalThe main part of the facility is located in underground tunnels. This is where the electrons are accelerated and induced to generate the X-ray radiation.
The two-kilometre-long main tunnel for the particle accelerator which brings the electrons to the required energy runs absolutely straight between the sites DESY-Bahrenfeld and Osdorfer Born. The particle beam is then distributed into a fan-shaped tunnel system located beneath the research campus Schenefeld, in which the particles generate the X-ray flashes by flying through special arrangements of magnets.
All the tunnels are located deep underground. For reasons of radiation protection and civil engineering, they have to be covered by around 5 to 6 metres of soil. Since the tunnels run mostly horizontally, their upper edge lies 6 to 38 metres beneath the surface, depending on the profile of the ground.
The accelerator tunnel and the tunnels of the fan-shaped system used for light generation have different diameters: Whereas an inner tunnel diameter of 5.30 metres is required for the accelerator, most tunnels of the “fan” have an inner diameter of 4.60 metres.
Access to the tunnels is provided by various shafts through which the components of the European XFEL will be brought underground and the supply pipes and cables led into the tunnels. In the construction phase, they will partly serve as start or end shafts for the tunnel boring machines. During operation of the facility, access to the tunnels and the neighbouring shaft areas is prohibited by a control system. The tunnels may be entered only during maintenance periods. Even then, access to each tunnel is strictly controlled, so that it is always known how many people are working in which tunnel.
