The SwissFEL X-ray Free Electron Laser (XFEL) facility started construction at the Paul Scherrer Institute (Villigen, Switzerland) in 2013 and will be ready to accept its first users in 2018 on the Aramis hard X-ray branch. In the following sections we will summarize the various aspects of the project, including the design of the soft and hard X-ray branches of the accelerator, the results of SwissFEL performance simulations, details of the photon beamlines and experimental stations, and our first commissioning results.

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The SwissFEL soft X-ray free-electron laser (FEL) beamline Athos will be ready for user operation in 2021. Its design includes a novel layout of alternating magnetic chicanes and short undulator segments. Together with the APPLE X architecture of undulators, the Athos branch can be operated in different modes producing FEL beams with unique characteristics ranging from attosecond pulse length to high-power modes. Further space has been reserved for upgrades including modulators and an external seeding laser for better timing control. All of these schemes rely on state-of-the-art technologies described in this overview. The optical transport line distributing the FEL beam to the experimental stations was designed with the whole range of beam parameters in mind. Currently two experimental stations, one for condensed matter and quantum materials research and a second one for atomic, molecular and optical physics, chemical sciences and ultrafast single-particle imaging, are being laid out such that they can profit from the unique soft X-ray pulses produced in the Athos branch in an optimal way.

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Abstract. The goal of SwissFEL is to provide a source of extremely bright and short X-ray pulses enabling scientific discoveries in a wide range of disciplines, from fundamental research to applied science. To accelerate the electrons to an energy of up to 5.8 GeV a linear accelerator (LINAC) consisting of 104 C-band (5.712 GHz) accelerating structures each of a length of 2m is foreseen. We present the mechanical design of the accelerating structures. High precision manufacturing is applied in order to avoid a tuning step during fabrication. Following this production process several 0.3 m test structures have been produced and tested. First results including RF power tests are presented. Description of linear accelerator (LINAC) of SwissFEL and of its general requirementsThe LINAC is used to accelerate an electron bunch to an energy of 5.8 GeV before the lasing process is initiated in the undulator section. One module consists of 4 C-band (5.7 GHz) structures made of copper which are fed by one pulse compressor connected to one modulator and to one klystron (figure 1). 26 modules or 104 C-band structures aligned along a row of 300 m are required to accelerate the electrons up to 5.8 GeV.To minimize cost and to achieve an economical series production of the C-band accelerating structures fabrication has to meet stringent requirements.• Precision of one single copper cell is of 1 µm and has a surface roughness R a of 25 nm.• Concentricity is 50 µm of a 2m C-band structure before and after vacuum brazing together in one step the J-shaped input and output couplers and the 113 copper cells (table 1).• No additional mechanical tuning of a 2m long C-band structure is required after brazing since all individual volumes of the 113 copper cells match the specified frequency (5.712 GHz) and the nominal phase advance of 120°.